Intrinsic Rate of Increase

Knowledge of population growth potential is crucial for studying population dynamics and for establishing management tactics for pest control. Estimation of population growth can be achieved with fertility life tables because they synthesize data on reproduction and mortality of a population. The Þve main parameters associated with a fertility life table are as follows: (1) the net reproductive rate (Ro), (2) the intrinsic rate of increase (r m ), 3) the mean generation time (T), (4) the doubling time (Dt), and (5) the Þnite rate of increase (). Jackknife and bootstrap techniques are used to calculate the variance of the r m estimate, which can be extended to the other parameters of life tables. Those methods are computer-intensive, their application requires the development of efÞcient algorithms, and their implementation is based on a programming language that encompasses quickness and reliability. The objectives of this article are to discuss statistical and computational aspects related to estimation of life table parameters and to present a SAS program that uses jackknife to estimate parameters for fertility life tables. The SAS program presented here allows the calculation of conÞdence intervals for all estimated parameters, as well as provides one-sided and two-sided t-tests to perform pairwise or multiple comparison between groups, with their respective P values.

Intraspecific density-dependent effects in the Barro Colorado Island (Panama) study area are far stronger, and involve far more species, than previously had been suspected. Significant effects on recruitment, many extremely strong, are seen for 67 out of the 84 most common species in the plot, including the 10 most common. Significant effects on the intrinsic rate of increase are seen in 54 of the 84 species. These effects are far more common than interspecific effects, and are predominantly of the type that should maintain tree diversity. As a result, the more diverse an area in the forest is, the higher is the overall rate of increase of the trees in that area, although sheer crowding has by itself a negative effect. These findings are consistent with, but do not prove, an important role for host-pathogen interactions (defined broadly) in the maintenance of diversity. Ways are suggested by which to test host-pathogen models and competing models. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Eriophyid mites have been considered to have a high potential for use as classical biological control agents of weeds. We reviewed known examples of the use of eriophyid mites to control weedy plants to learn how effective they have been. In the past 13 years, since Rosenthal's 1996 review, 13 species have undergone some degree of pre-release evaluation (Aceria genistae, A. lantanae, Aceria sp. [boneseed leaf buckle mite (BLBM)], A. salsolae, A. sobhiani, A. solstitialis, A. tamaricis, A. thalgi, A. thessalonicae, Cecidophyes rouhollahi, Floracarus perrepae, Leipothrix dipsacivagus and L. knautiae), but only four (A. genistae, Aceria sp. [BLBM], C. rouhollahi and F. perrepae) have been authorized for introduction. Prior to this, three species (Aceria chondrillae, A. malherbae and Aculus hyperici) were introduced and have become established. Although these three species impact the fitness of their host plant, it is not clear how much they have contributed to reduction of the popu...

Theory predicts that populations of animals with late maturity, low fecundity, large body size and low body growth rates will have low potential rates of population increase at low abundance. If this is true, then these traits may be used to predict the intrinsic rate of increase for species or populations, as well as extinction risks. We used life-history and population data for 63 stocks of commercially exploited fish species from the northeast Atlantic to test relationships between life-history parameters and the rate of population increase at low abundance. We used cross-taxonomic analyses among stocks and among species, and analyses that accounted for phylogenetic relationships. These analyses confirmed that largebodied, slow-growing stocks and species had significantly lower rates of recruitment and adult production per spawning adult at low abundance. Furthermore, high ages at maturity were significantly correlated with low maximum recruit production. Contrary to expectation, fecundity was significantly negatively related to recruit production, due to its positive relationship with maximum body size. Our results support theoretical predictions, and suggest that a simply measured life-history parameter can provide a useful tool for predicting rates of recovery from low population abundance.

The discovery of soybean aphid, Aphis glycines Matusumura, in North America in 2000 provided the opportunity to investigate the relative strength of top-down and bottomup forces in regulating populations of this new invasive herbivore. At the Kellogg Biological Station Long Term Ecological Research site in agroecology, we contrasted A. glycines establishment and population growth under three agricultural production systems that differed markedly in disturbance and fertility regimes. Agricultural treatments consisted of a conventional-tillage high-input system, a no-tillage high-input system, and a zero-chemicalinput system under conventional tillage. By selectively restricting or allowing predator access we simultaneously determined aphid response to top-down and bottom-up influences. Irrespective of predator exclusion, our agricultural manipulations did not result in bottom-up control of A. glycines intrinsic rate of increase or realized population growth. In contrast, we observed strong evidence for top-down control of A. glycines establishment and overall population growth in all production systems. Abundant predators, including Harmonia axyridis, Coccinella septempunctata, Orius insidiosus, and various predaceous fly larvae, significantly reduced A. glycines establishment and population increase in all trials. In contrast to other systems in which bottom-up forces control herbivore populations, we conclude that A. glycines is primarily controlled via top-down influences of generalist predators under a wide range of agricultural management systems. Understanding the role of top-down and bottomup forces in this context allows agricultural managers to focus on effective strategies for control of this invasive pest.

Measurements of toxicity based on individuals, such as the LC50 (concentration that kills 50% of a population), and effects on reproduction are used extensively in determining ecological risk, in particular, for endangered or threatened species. An underlying assumption is that individual-based toxicity metrics for one species can be directly compared with that for another species. However, this assumption overlooks the fact that different species have different life-history strategies and variables, such as lifespan, time to first reproduction, and number of offspring produced over a lifetime. Using a simple model and laboratoryderived parameter values, we tested the impact of differences in life-history traits on predicted responses to stress. The model predicts the delay in population growth. We compared seven invertebrate species by imposing 50% chronic mortality, 50% reduction of offspring, and both of these effects. The model predicted substantial differences in population delay among all of the species. Furthermore, the intrinsic rate of increase of each population was negatively correlated with the delay in population growth; species with high intrinsic rates of increase were less susceptible to equal levels of stress than species with lower intrinsic rates of increase. These results suggest that the susceptibility of species to pollutants is more complicated than previously thought and that differences in life-history variables must be considered in analyses of population persistence for threatened and endangered species.

Coffee is predicted to be severely affected by climate change. We determined the thermal tolerance of the coffee berry borer , Hypothenemus hampei, the most devastating pest of coffee worldwide, and make inferences on the possible effects of climate change using climatic data from Colombia, Kenya, Tanzania, and Ethiopia. For this, the effect of eight temperature regimes (15, 20, 23, 25, 27, 30, 33 and 35uC) on the bionomics of H. hampei was studied. Successful egg to adult development occurred between 20-30uC. Using linear regression and a modified Logan model, the lower and upper thresholds for development were estimated at 14.9 and 32uC, respectively. In Kenya and Colombia, the number of pest generations per year was considerably and positively correlated with the warming tolerance. Analysing 32 years of climatic data from Jimma (Ethiopia) revealed that before 1984 it was too cold for H. hampei to complete even one generation per year, but thereafter, because of rising temperatures in the area, 1-2 generations per year/coffee season could be completed. Calculated data on warming tolerance and thermal safety margins of H. hampei for the three East African locations showed considerably high variability compared to the Colombian site. The model indicates that for every 1uC rise in thermal optimum (T opt.), the maximum intrinsic rate of increase (r max) will increase by an average of 8.5%. The effects of climate change on the further range of H. hampei distribution and possible adaption strategies are discussed. Abstracts in Spanish and French are provided as supplementary material Abstract S1 and Abstract S2.

Background: Insecticide resistance is one of the best examples of rapid micro-evolution found in nature. Since the development of the first synthetic insecticide in 1939, humans have invested considerable effort to stay ahead of resistance phenotypes that repeatedly develop in insects. Aphids are a group of insects that have become global pests in agriculture and frequently exhibit insecticide resistance. The green peach aphid, Myzus persicae, has developed resistance to at least seventy different synthetic compounds, and different insecticide resistance mechanisms have been reported worldwide.

Even though Bayesian methods can provide statistically rigorous assessments of the biological status of fisheries resources, uninformative data (e.g., declining catch rate series with little variation in fishing effort) can produce highly imprecise parameter estimates. This can be counteracted with the use of informative Bayesian prior distributions (priors) for model parameters. We develop priors for the intrinsic rate of increase (r) in the Schaefer surplus production model using demographic methods and illustrate the utility of this with an application to large coastal sharks in the Atlantic. In 1996, a U.S. stock assessment obtained a point estimate for r of 0.26. For such long-lived and low-fecund organisms, this could potentially be too high. Yet it was used to predict that within about 10 years, a 50% reduction in the 1995 catch level should result in >50% chance of increasing the population to the abundance required to produce maximum sustainable yield. In contrast, a Bay...

, a total of at least 3368 southern right whales Eubalaena australis were taken by Soviet whaling expeditions in the Southern Hemisphere, despite the species being internationally protected since 1935. These catches and the associated biological data (presented here for the ®rst time) represent a unique source of information on the distribution, movements, size composition, reproduction and feeding of southern right whales during summer months. Revelation of these previously unreported catches also has implications for the assessment of the current status of right whale stocks. Incorporation of the Soviet catches into population assessments generally leads to higher estimates of the size of the population at protection, but the relative increase in this size depends on the intrinsic rate of increase in the population. #

Sawfish are a group of endangered elasmobranchs that were common in tropical inshore, estuarine and freshwaters. The demography of two species of sawfish that occur in the western Atlantic -Pristis pectinata and P. perottetiwas investigated using age-structured life tables. Life history parameters for use in the life tables were obtained from published data. Five scenarios were tested for P. pectinata to incorporate uncertainties about life history data. Values of intrinsic rate of increase ranged from 0.08 to 0.13 yr −1 , and population doubling times from 5.4 to 8.5 yrs. Eight scenarios were tested for P. perotteti. The most likely range for the intrinsic rate of increase was 0.05-0.07 yr −1 , with population doubling times of 10.3-13.5 yrs. Four scenarios investigating the sensitivity to methods of estimating natural mortality produced similar results. The demographic results were sensitive to changes in reproductive periodicity and natural mortality. The results indicate that if effective conservation plans can be implemented for sawfish and sawfish habitats, recovery to levels where there is little risk of extinction will take at least several decades.

The life history of the oriental latrine fly, Chrysomya megacephala (Fabricius), was studied at 26°C in the laboratory. The raw data were analyzed based on the age-stage, two-sex life table, in order to take both sexes and the variable developmental rate among individuals and between sexes into consideration. The intrinsic rate of increase (r), the finite rate of increase (k), the net reproduction rate (R 0 ) and the mean generation time (T) of C. megacephala were 0.2182, 1.2438 d -1 , 91.7 offspring/individual and 20.7 days, respectively. The life expectancy of a newborn egg is 32 days. The maximum reproductive value of females is on the 19th day, which coincides with the total pre-oviposition period counted from birth. The two-sex life table analysis gives a comprehensive description of the stage differentiation of C. megacephala.

Biological invasions pose a great threat to the integrity of natural communities. Some invasive species demonstrate a population explosion shortly after arrival while in other cases a prolonged lag between arrival and population outbreak is evident. This paper describes a case of a prolonged lag and explores the possible mechanism for this lag. The Red Sea mussel Brachidontes pharaonis, a Lessepsian migrant, was first recorded in the Mediterranean seven years after the opening of the Suez Canal in 1869. Since then it spread along the Israeli coast and as far northwest as Sicily. Studies conducted in the late 1970s, when B. pharaonis was still rare, predicted that it would not establish dense populations along the Israeli coast and would not outcompete the indigenous mussel Mytilaster minimus, although it has strong negative effects on survival and growth of the native species. It was attributed to the invader's low intrinsic rate of increase relative to that of the native species, and to strong density-independent mortality generated by exposure to high wave action and sedimentation. In contrast to these predictions, we found massive formations of B. pharaonis beds after lag of about 120 years. We looked for distributional patterns that may explain this lag and found no south-north gradient but a strong habitat-dependent colonization. Most apparent are dense B. pharaonis mussel beds (density >300 per 100 cm 2 ) on rocky platforms where mussel beds were absent in the past. These platforms lack the vermetid rim that is typical to this formation. In platforms protected by a biogenic rim, sediment accumulation is high and perennial algae flourish. None of the mussel species form beds in such habitats. We suggest that the delayed formation of B. pharaonis beds along the Israeli coast is a consequence of a recent shift in habitat conditions on some platforms. It is possible that receding of the biogenic rim at the edge of these platforms allowed more effective washing, reduced sediment accumulation, and reduced perennial algae cover making platforms more suitable for the mussels. Lower density-independent mortality allowed B. pharaonis to dominate on such platforms over the indigenous species. On beachrock, a habitat previously dominated by M. minimus, we recorded a rapid shift in numerical domination to B. pharaonis (from 1 : 7 to 1.4 : 1 Brachidontes/Mytilaster individuals) over a period of 4 years (1995)(1996)(1997)(1998)(1999). This is probably a result of saturation of the habitat by B. pharaonis recruits originating from the established populations on platforms. Salinity changes and a potential genetic shift may also have contributed to the invasive mussel outbreak.

Prosimian lemurs differ fundamentally from anthropoid primates in many traits related to social structure. By exploring the demography of Milne-Edwards' sifakas (Propithecus diadema edwardsi), and comparing it to other well-studied primates, we explore the effect of demographic and life-history factors on social structure. Specifically, we compare lemur survivorship and fertility patterns to two published composite models: one created for New World and another created for Old World monkeys. Using longitudinal data collected on individual Propithecus diadema edwardsi from four study groups from 1986 -2000 in Ranomafana National Park, Madagascar, we quantify 1) group composition, 2) birth seasonality, 3) interbirth interval, 4) life-table values, and 5) population growth estimates. The mortality, survivorship, and life-expectancy schedules indicate high infant and juvenile mortality. Fertility remains high until death.

In order to explore mechanistic linkages between low-frequency ocean/climate variability, and fish population responses, we undertook comparative studies of time-series of recruitment-related productivity and the biomass levels of fish stocks representing five life-history strategies in the northern North Pacific between the 1950s and the present. We selected seven species: Japanese sardine (Sardinopus melanostictus) and California sardine (Sardinopus sagax) (opportunistic strategists), walleye pollock (Theragra chalcogramma, intermediate strategist), pink salmon (Oncorhynchus gorbuscha, salmonic strategist), sablefish (Anoplopoma fimbria) and Pacific halibut (Hippoglossus stenolepis) (periodic strategists) and spiny dogfish (Squalus acanthias, equilibrium strategist). The responses in terms of productivity of sardine, pink salmon, sablefish and halibut to climatic regime shifts were generally immediate, delayed, or no substantial responses depending on the particular regime shift year and fish stock (population). In walleye pollock, there were some periods of high productivity and low productivity, but not coincidental to climatic regime shifts, likely due to indirect climate forcing impacts on both bottom-up and topdown processes. Biomass of zooplankton and all fish stocks examined, except for spiny dogfish whose data were limited, indicated a decadal pattern with the most gradual changes in periodic strategists and most intensive and rapid changes in opportunistic strategists. Responses of sardine productivity to regime shifts were the most intense, probably due to the absence of density-dependent effects and the availability of refuges from predators when sardine biomass was extremely low. Spiny dogfish were least affected by environmental variability. Conversely, spiny dogfish are likely to withstand only modest harvest rates due to their very low intrinsic rate of increase. Thus, each life-history strategy type had a unique response to climatic forcing, owing to their inherent biological traits such as mode, frequency and intensity of reproduction, early life style, age of maturity and longevity. On the other hand, responses of different stocks within a species to climatic regime shifts were unique to each local region, because large-scale climatic forcings are modulated by local physical, chemical and biological processes. The observed response time or absence of response in recruitment-related fish productivity to climatic regime shifts may be influenced by (1) local environmental conditions (immediate, with a delay or no effects), (2) phenological shifts in zooplankton life-history (immediate or with a delay), and (3) stochastic episodic events in both top-down and bottom-up processes (immediate, with a delay or no effects).

This article investigates the mean abundances of trophic levels in simple models of two-and three-level food chains as a function of the rate of input of nutrients. The analysis concentrates on cases in which the equilibrium point with all species present is unstable. In most of the models, the instability arises because the consumer species become satiated when food density is high. In unstable two-level systems, bottom level abundance generally increases with increased nutrient input. The abundance of the second level may decrease with increased input. Changes in the intrinsic rate of increase and carrying capacity of the bottom level can have qualitatively opposite effects on trophic level abundances. Refuges for or immigration of the bottom level usually cause both levels to increase in mean abundance with an increased carrying capacity. A variety of different predator-prey models are discussed briefly and the results suggest that increased nutrient input will often increase the abundance of both levels; however, several circumstances can cause the top level to decrease. In three-level systems, an increased carrying capacity can cause extinction of the top level. Extinction may or may not be conditional on the initial densities of the three levels. These results may help explain the observed lack of correlation between productivity and the number of trophic levels in natural food webs, as well as the lack of very long food chains. The results suggest that patterns of abundances across productivity gradients cannot be used to assess the importance of top-down vs bottom-up effects.

Natural populations of Daphnia pulex that reproduce by obligate parthenogenesis include a number of clones. Studies on two common and two rare clones from southwestern Ontario revealed significant differences in their intrinsic rates of increase, competitive abilities, rates of ephippial egg production, and lifespans. Environmental factors such as temperature and food type had large influences on the rate of increase of each clone. Differences in rates of increase among clones were most pronounced at temperatures higher than those encountered in nature. In general, the covariance of life history traits among clones was high. The outcome of competitive encounters between clones was deterministic and in most cases was unaffected by temperature. Clones with high rates of increase tended to be better competitors than those with low rates of increase.

Abstract: The reproductive potential and longevity of Podisus nigrispinus (Dallas) were determined under laboratory conditions at a constant temperature of 25°C. The data were used to calculate life-fertility tables and rates of increase. The fecundity plateau of P. nigrispinus lasted 18 days, and during this period mean fecundity was 8.89 eggs per female per day. It started at the eighth day of age and ended at the 18th day of age. The declining fecundity period started at 18 days of age and ended with the death of the females. The female of P. nigrispinus oviposited a mean of 188.54 eggs, and had a mean longevity of 31.21 days. The gross reproductive rate (GRR) was 104.374 females/female; the net reproductive rate (Ro) was 31.945 females/female; the generation time was 47.390 days; the doubling time was 9.480 days; the intrinsic rate of increase (rm) was 0.073, and the finite rate of increase (λ) was 1.076. The predator population increased by 16.61 adult progeny per female per generation in the laboratory.

Effects of sublethal azadirachtin exposure to the biological performance of Tetranychus urticae Koch was studied under laboratory conditions. Bioassay was used to asses the effect of different concentrations of azadirachtin on longevity, fecundity, fertility, and offspring development. Azadirachtin (64 and 128 ppm) affected fecundity and mortality but had no effect on fertility and offspring development. A subsequent life-table study with 80 ppm of azadirachtin found that the compound caused a reduction of 50% in survival to adult stage. The peak of reproduction was reached at 5 days causing a decrease in the mean fecundity to almost eight times than of untreated females. The net reproductive rate (R 0 ), the intrinsic rate of increase (r m ), and the finite rate of increase (k) of treated females were lower. Treatment showed a negative value of r m , resulting in a declining population. These results suggest that azadirachtin could be incorporated in Integrated Pest Management (IPM) programmes of T. urticae.

Development, imaginal survivorship, adult longevity and fecundity of the predatory phytoseiid mite Euseius (Amblyseius) finlandicus Oudemans reared on seven different plant pollens were determined in the laboratory. The rationale behind these experiments was to assess the nutritional value and the possible effect on development and population dynamics of the mite. Mites were kept individually on bean (Phaseolus vulgaris L.) leaf disks at 20 Ϯ 1ЊC and a photoperiod of 16:8 (L:D) h, with a sufÞcient quantity of pollen of apple (Malus silvestris M.), pear (Pyrus communis L.), cherry (Prunus avium L.), peach (Prunus persica L.), apricot (Prunus armeniaca L.), walnut (Juglans regia L.), or poppy (Papaver rhoeas L.). Developmental time from neonate larva to adult emergence varied between the different pollens from 6.03 to 6.62 d for females and from 5.46 to 6.14 d for males. Survivorship during immature development varied from 67.2 to 95.9% with the lowest value recorded on peach pollen. The average life span of adult females reared on the different pollens varied from 18.2 to 56.2 d, whereas the respective total fecundity ranged from 2.5 to 46.5 eggs per female. The estimated values of the intrinsic rate of increase (r m) varied from 0.012 to 0.150. The analysis of these results show that cherry, peach, apricot, walnut, and poppy pollens are of higher nutritional value for E. finlandicus than apple and pear pollens and thus may play an important role in the Þeld for sustaining and increasing the predatorÕs population.

Leslie matrices and life tables are demographic models commonly used to evaluate the ability of specific elasmobranch life history strategies to sustain given levels and patterns of fishing pressure. These models are generally density independent and provide an instantaneous rate of population growth for a specified set of life history traits that correspond to a specific population size. Many investigators are using these models to compute rates of population growth that they claim are estimates of the maximum population growth rate (r intrinsic ); they then use these estimates to compute purported estimates of maximum sustainable fishing mortality. However, neither a Leslie matrix nor a life table can be used to estimate r intrinsic without additional information, except in the special case where a severely depleted population is modeled. Only in a severely depleted population will competition for resources be at a minimum and both density-dependent compensation and the rate of population growth be at a maximum (i.e., at r intrinsic ). The fundamental problem is to determine the life history parameters that would occur if the population were extremely depleted because extensive observations on extremely depleted populations are rare. In the absence of such data, r intrinsic can only be estimated from these types of density-independent models by extrapolating observed population growth rates toward zero population size. We illustrate the problems in, and describe methods for, estimating r intrinsic and present information on two species of elasmobranch: barndoor skate Dipturus laevis and lemon shark Negaprion brevirostris.

The age-specific fecundity of Trichogramma evanescens Westwood and T. cacoeciae Marchal (Hymenoptera: Trichogrammatidae) with Ephestia elutella (Hübner) (Lepidoptera: Pyralidae: Phycitinae) as host and the life span of the adults with and without hosts was determined at 20, 26, 30 and 35 • C and 75 ±5% r.h. in the laboratory. At 35 • C, no progeny emerged. The availability of hosts prolonged the longevity in both species. Longevity, percentage of parasitism, fecundity, and the intrinsic rate of natural increase were higher in T. evanescens than in T. cacoeciae. Trichogramma evanescens is expected to be more effective than T. cacoeciae for use in biological control of Ephestia spp., especially at low and high temperatures.

Plant features that enhance predator effectiveness can be considered extrinsic-resistance factors because they result in reduced insect herbivory. In this paper we test the hypothesis that reduced epicuticular wax (EW) in Pisum sativum L. is an extrinsic-resistance factor contributing to field resistance to Acyrthosiphon pisum (Harris). We monitored pea aphid populations in the field on reduced EW and normal EW near isolines of peas for two seasons and confirmed that aphid populations are lower on reduced EW peas than on normal EW peas. We also monitored predators within the canopies of the two pea lines to discover community level patterns in response to differences in EW. We found that while predator numbers were similar between the two lines, there were more syrphids on the normal EW peas, and a trend towards more coccinellids on reduced EW peas. We tested the impact of predators on pea aphids on the two EW lines by monitoring their population levels in cages that excluded predators, and in cages that allowed predators to enter. We found that pea aphid populations were similar on the two EW lines when predators were excluded. When predators were allowed access to the plants, pea aphid populations were reduced more on reduced EW peas than on normal EW peas. We also examined the intrinsic resistance to aphids in reduced EW peas with laboratory dual-choice tests comparing aphid response to reduced EW and normal EW peas, and found that walking, apterous aphids displayed no preference for one pea line over the other. Bioassays to measure growth and fecundity of the pea aphid on the two EW types in the greenhouse and in the field showed that intrinsic rate of increase, and other life table parameters, were not different for aphids on the two lines. Together these results support the hypothesis that reduced EW in peas is a predator-dependent extrinsic resistance factor. Genetically reducing EW bloom in peas and other waxy crop plants might improve the effectiveness of arthropod natural enemies of insect pests. More generally, the results show that a subtle change in plant morphology can substantially influence the impact of predators on insect herbivore populations. The benefit of extrinsic resistance to herbivory conferred by reduced EW may balance any benefits of a prominent EW bloom, thereby sustaining EW polymorphisms in some natural plant populations.

The evolution of population dynamics in a stochastic environment is analysed under a general form of density-dependence with genetic variation in r and K, the intrinsic rate of increase and carrying capacity in the average environment, and in s e 2 , the environmental variance of population growth rate. The continuous-time model assumes a large population size and a stationary distribution of environments with no autocorrelation. For a given population density, N, and genotype frequency, p, the expected selection gradient is always towards an increased population growth rate, and the expected fitness of a genotype is its Malthusian fitness in the average environment minus the covariance of its growth rate with that of the population. Long-term evolution maximizes the expected value of the density-dependence function, averaged over the stationary distribution of N. In the q-logistic model, where density dependence of population growth is a function of N q , long-term evolution maximizes E[N q ]Z[1Ks e 2 /(2r)]K q . While s e 2 is always selected to decrease, r and K are always selected to increase, implying a genetic trade-off among them. By contrast, given the other parameters, q has an intermediate optimum between 1.781 and 2 corresponding to the limits of high or low stochasticity.

Illinoia pepperi (MacGillivray) infests cultivated highbush blueberries, Vaccinium corymbosum L., in the Northeastern United States. Allopatric resistance to I. pepperi was examined in Vaccinium darrowi Camp, which evolved in the absence of I. pepperi in the Southeastern U.S. V. corymbosum cv. "Elliott", was used as a susceptible control. Between population variability in I. pepperi resistance was assessed by measuring length of the prereproductive period, fecundity, and survivorship on 14 V. darrowi accessions representing 11 discrete wild populations. Length of I. pepperi's prereproductive period and survivorship were not significantly affected. However, differences were detected in fecundity and the intrinsic rate of increase (r m ). Within population variability in resistance was measured by confining first instars to 24 accessions from a single wild population of V. darrowi (NJ88-06). Significant differences in the mean total number of aphids occurring after 20 d were only detected between 2 of the 24 V. darrowi accessions. A greater degree of diversity in I. pepperi resistance exists between populations of V. darrowi compared to within a population. Constitutive leaf and stem polyphenolics were identified by HPLC-MS and quantified from 14 of the V. darrowi accessions. The accessions varied in concentrations of five phenolic acids and seven flavonol glycosides, but a correlation was not found between individual or total phenolics and aphid performance. Overall, screening within and between populations of V. darrowi identified promising sources of aphid resistance, but J Chem Ecol phenolic acid and flavonol glycoside profiles did not predict resistance levels. The mechanism of resistance remains to be identified. a Means within columns followed by the same letter are not significantly different [a±0.05; Tukey's studentized range (HSD) test]. N±9 for all accessions b The first value in the population ID (e.g., NJ88-15-09) represents the year of collection, the second value represents the population number, and the third value represents the specimen number. c From birth to reproductive maturity d Total offspring produced over a period of 42 d after birth J Chem Ecol

Studies were conducted to examine the effect of potassium (K) on soybean aphid, Aphis glycines Matsumura, population growth. A laboratory feeding assay examined the effect of K-deÞcient foliage on life table parameters of soybean aphids, and Þeld experiments were designed to determine the effect of three soil K treatment levels on aphid populations and their impact on soybean yields. The feeding assay found that life table parameters differed between aphids feeding on the K-deÞcient and nondeÞcient soybean leaves. Soybean aphids in the K-deÞcient treatment exhibited signiÞcantly greater intrinsic rate of increase (r m ), Þnite rate of increase (), and net reproductive rate (R o ) relative to aphids feeding on nondeÞcient leaves. No signiÞcant difference was observed in mean generation time (T) between the two treatments. However, the Þeld experiment repeated over 2 yr showed no effect of K on soybean aphid populations. Soybean aphid populations were high in unsprayed plots and feeding resulted in signiÞcant yield losses in 2002 at all three K treatment levels: when averaged across 2001 and 2002, unsprayed treatments yielded 22, 18, and 19.5% less than the sprayed plots in the low, medium, and high K treatments, respectively. No signiÞcant interaction was observed between aphid abundance and K level on soybean yields in either year. This study therefore suggests that although aphids can perform better on K-deÞcient plants, aphid abundance in the Þeld may be dependent on additional factors, such as dispersal, that may affect Þnal densities within plots.

Reproductive and population parameters were calculated for six tephritid fly braconid parasitoids: Fopius arisanus (Sonan), Diachasmimorpha longicaudata (Ashmead), Fopius vandenboschi (Fullaway), Psyttalia incisi (Silvestri), Diachasmimorpha tryoni (Cameron), and Psyttalia fletcheri (Silvestri), reared on a preferred fruit fly host: oriental fruit fly, Bactrocera dorsalis (Hendel), Mediterranean fruit fly, Ceratitis capitata (Wiedemann), or melon fly, Bactrocera cucurbitae (Coquillett). Highest numbers of eggs were produced by F. arisanus, D. longicaudata, and P. incisi. Numbers of P. fletcheri eggs produced were intermediate and those for D. tryoni and F. vandenboschi lowest. Intrinsic rates of increase were highest for F. arisanus (0.12 per female per day) and D. longicaudata (0.12 per female per day) and lowest for F. vandenboschi (0.08 per female per day). Highest net reproductive rates were obtained for P. incisi (29.4) and lowest for F. vandenboschi (10.1). Mean generation times ranged from 27.2 days for D. longicaudata to 33.4 days for P. incisi. All parasitoid species survived less than 50 days, except P. incisi which survived 133 days. Parasitoid species were shorter-lived and possessed lower reproductive rates than their fruit fly counterparts. For example, parasitoid generation times were 24.3%, 26.8%, and 11.7% shorter for F. arisanus, D. tryoni, and P. fletcheri reared on oriental fruit fly, Mediterranean fruit fly, and melon fly, respectively; however, intrinsic rates of increase were 25%, 44%, and 26.6% lower. Implications of these studies are discussed with respect to past and future biological control programs for fruit flies in Hawaii. Ó 2002 Elsevier Science (USA). All rights reserved.

A central question in evolutionary biology concerns the ecological and genetic processes by which species hybridize. We analyze the evolutionary consequences of hybridization, biogeographic patterns and fitness comparisons in the crustacean Daphnia (Branchiopoda) within the conceptual framework of theories on interspecific hybridization. In contrast to most cases of hybridization among animals, Daphnia species and hybrids do not form interpopulational transition zones (hybrid zones), but rather patchy distributions of hybrids and parentals have been found. In addition, due to ameiotic parthenogenetic reproduction, hybrid breakdown can be avoided and hybrids can reach higher abundances than parental species. Hybrids within the D. galeata complex occur across broad geographic ranges, and lakes vary significantly in species and hybrid composition over time. Species differ in traits related to predator avoidance, such as size at maturity, intrinsic rate of increase (r), behaviour, and induction of helmets and spines. Hybrids tend to exhibit a combination of characters which enables them to persist in ecological niches which arise seasonally due to changes in predation and food regimes. Hybrids seem to be of recent and multiple origin and seem to form backcrosses occasionally, but no mitochondrial and only low levels of nuclear introgression have been detected. Interspecific matings are non-random, which leads to directionality of hybridization and introgression. Environmental settings seem to facilitate hybridization (temporal hybrid superiority model), whereas evolutionary consequences may arise from repeated backcrossing, which in some cases results in patterns of reticulate evolution.

The management of Tetranychus urticae, a key pest of clementine trees, is mainly based on the use of acaricides. However, more environmentally safe measures, such as biological control, are being encouraged. Life-history traits of the three most abundant phytoseiid mites associated with T. urticae on this crop (Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus) were studied. The experiments were performed under laboratory conditions (25°C, 80 ± 5% RH and 16:8 h (L:D)) on clementine leaves and T. urticae as prey. Euseius stipulatus could not complete its life cycle, whereas P. persimilis and N. californicus completed it satisfactorily. The estimated intrinsic rate of increase (r m) was significantly higher for P. persimilis (0.344 day−1) than for N. californicus (0.244 day−1) and both were higher than the r m value of T. urticae on clementine leaves. Implications of these results for the biological control of T. urticae in this crop are discussed.

Biological invasions are constantly gaining recognition as a significant component of global change. The Mediterranean fruit fly (medfly) constitutes an ideal model species for the study of biological invasions due to its (1) almost cosmopolitan geographic distribution, (2) huge economic importance, and (3) welldocumented invasion history. Under a common garden experimental set up, we tested the hypothesis that medfly populations obtained from six global regions [Africa (Kenya), Pacific (Hawaii), Central America (Guatemala), South America (Brazil), Extra-Mediterranean (Portugal), and Mediterranean (Greece)] have diverged in important immature life-history traits such as preadult survival and developmental times. We also tested the hypothesis that medfly populations from the above regions exhibit different population growth rates. For this purpose, data on the life history of immatures were combined with adult survival and reproduction data derived from an earlier study in order to calculate population parameters for the above six populations. Our results clearly show that medfly populations worldwide exhibit significant differences in preadult survival, developmental rates of immatures and important population parameters such as the intrinsic rate of increase. Therefore, geographically isolated medfly populations may share different invasion potential, since population growth rates could influence basic population processes that operate mostly during the last two stages of an invasion event, such as establishment and spread. Our findings provide valuable information for designing population suppression measures and managing invasiveness of medfly populations worldwide.

The development, survival, and fecundity of Scymnus subvillosus (Goeze) (Coleoptera: Coccinellidae) were studied at 20, 25, 30, and 35ЊC, 60 Ϯ 5% RH, and a photoperiod of 16:8 (L:D) h (5,000 lux) under laboratory conditions. The total developmental time from egg hatch to adult eclosion ranged from 22.6 d at 20ЊC to 10.6 d at 35ЊC. The developmental rates of the egg stage, the larval stage, and total preadult stage at different temperatures increased linearly with increasing temperature. The thermal summation of the egg stage, the larval stage, and the total preadult stage was 77.5, 145.8 and 300 degree-days (DD), respectively. The developmental threshold of the egg stage, the larval stage, and the total preadult stage was 7.4, 4.1, and 7.1ЊC, respectively. The life history raw data were analyzed using the age-stage, two-sex life table. The intrinsic rate of increase was 0.0845, 0.1138, 0.1395, and 0.0668 d Ϫ1 at 20, 25, 30, and 35ЊC, respectively. The net reproductive rate was highest at 25ЊC (R 0 ϭ 78.7), and lowest at 35ЊC (R 0 ϭ 4.7). The mean generation time was shortest at 35ЊC (T ϭ 23.9 d). The life table data can be used for the projection of population growth and designing mass rearing programs. Ö ZET Scymnus subvillosus (Goeze) (Coleoptera: Coccinellidae)Õun dö rt farklõ sõcaklõk (20, 25, 30, ve 35ЊC), % 60 Ϯ 5 orantõlõ nem ve 16 saat aydõnlatmalõ (5000 Lü x) laboratuvar koşullarõnda gelişme, canlõ kalma oranõ ve ü remesi incelenmiştir. Yumurtadan ergine gelişme sü resi 22.6 gü n (20ЊC) ile 10.6 gü n (35ЊC) arasõnda deg işmiştir. Yumurta ve larva dö nemleri ile toplam ergin ö ncesi dö nemin gelişme oranõ sõcaklõktaki artõşla birlikte dog rusal olarak artmõştõr. Yumurta, larva ve toplam ergin ö ncesi dö nemlerin gelişmesi iç in gereksinim duyulan etkili sõcaklõklar toplamõ sõrasõyla 77.5, 145.8 ve 300 gü n-derece, bu dö nemlerin gelişme eşig i sõcaklõklarõ ise sõrasõyla 7.4, 4.1, ve 7.1ЊC olarak hesaplanmõştõr. Elde edilen verilerden yaşa bag lõ, iki eşeyli yaşam ç izelgesi analizi ile yaşam ç izelgesi parametreleri oluşturulmuştur. Avcõnõn kalõtsal ü reme yeteneg i deg erleri 20, 25, 30, ve 35ЊC de sõrasõyla 0.0845, 0.1138, 0.1395 ve 0.0668 gü n Ϫ1 olarak bulunmuştur. En yü ksek net ü reme gü cü deg eri 25ЊC de (R 0 ϭ 78.7), en dü şü k ise 35ЊC de (R 0 ϭ 4.7) elde edilmiştir. En kõsa ortalama dö l sü resi deǧ eri 35ЊC de (T ϭ 23.9 gü n) elde edilmiştir. Bu ç alõşma sonucunda elde edilen yaşam ç izelgesi verilerinin avcõnõn populasyon gelişmesinin tahmininde ve kitle ü retim programõnõn dü zenlenmesinde kullanõlabileceg i sonucuna varilmiştõr.

The intertidal copeopod Tigriopus japonicus, which is abundant and widely distributed along the coasts of Western Pacific, has been suggested to be a good marine ecotoxicity testing organism. In this study, a series of experiments were conducted to investigate the reproducibility and variability of copper (Cu) sensitivity of T. japonicus so as to evaluate its potential to serve as an appropriate test species. To understand the seasonal variation of Cu sensitivity, individuals of T. japonicus were collected from the field in summer and winter, and subjected to standard 96 h acute (static renewal) toxicity tests. 96 h-LC50 values of T. japonicus collected from the two seasons were marginally different (p = 0.05), with an overall coefficient of variation (CV) of 33%. Most importantly, our results indicated that chronic Cu sensitivity of T. japonicus was highly reproducible. The CVs of intrinsic rates of increase in the population of the control and Cu treatment (10 lg Cu l À1 ) groups were only 10-11% between 10 runs of a standardised complete life-cycle test. Moreover, different Cu(II) salts generally resulted in a similar 96 h-LC50 value while Cu(I) chloride was consistently slightly less toxic than Cu(II) salts. Given such a high reproducibility of toxic responses, it is advocated to use T. japonicus as a routine testing organism.

Studies on success or failures of biological invasions by different insect biotypes are scarce and could provide interesting insights into the traits that determine greater or lower ability to invade. Life history traits of invasive whiteflies Bemisia tabaci of the B biotype (known as a worldwide invasive biotype) and of the indigenous biotype Ms (not known as an invader anywhere in the world), both from the island of La Réunion (Indian Ocean), were compared for this purpose. In our study we demonstrated that within a cultivated host plant (tomato), the B biotype differs from the Ms by a combination of several life-history traits. This combination gives the invasive biotype an advantage over the resident both in terms of rapid demographic growth (increased intrinsic rate of increase and associated traits such as short developmental times and high fecundity) and in terms of competition (large adult and offspring sizes), without any recorded trade off. However, in the field the resident biotype remains dominant on non-cultivated hosts (weeds) and in a particular climate (high humidity). This suggests that invasive biotypes are characterized by physiological, morphological and biological adaptations to a disturbed environment created by anthropic activities at different places in the world, while resident biotypes may persist in less altered habitats.

Demographic parameters of Diuraphis noxia (Mordvilko) and its parasitoid, Diaeretiella rapae (McIntosh) were investigated under laboratory conditions at temperatures of 20 + 18C, 60 + 5% relative humidity of 60 + 5% and a photoperiod of 16: 8 (light: dark) hours. The survival rates (l x) and the life expectancy (e x) at the beginning of adult emergence were 86% and 25.81 days for D. noxia and 100% and 7.36 days for D. rapae, respectively. Based on the Weibull distribution parameters, the survival curves were type I for both D. noxia and D. rapae, which indicates that mortality mostly occurred in older stages. The r m-values in aphid and parasitoid were obtained as 0.22 + 0.002 and 0.19 + 0.003 day 71 , respectively. Mean generation time (T) and doubling time (DT) were 15.93 + 0.202 and 3.15 + 0.031 days for the aphid and 15.33 + 0.071 and 3.67 + 0.054 days for the parasitoid, respectively. The R 0-values of D. noxia and D. rapae were evaluated 33.19 + 0.961 and 18.07 + 0.761 females/female/generation, respectively. The gross and net fecundity rates were 59.21 + 1.94 and 32.825 + 0.972 nymphs/ female/day for the aphid and 37.59 + 1.46, and 33.8 + 1.51 eggs/female/day for the parasitoid, respectively. The results of this research indicated that D. rapae is an adequate parasitoid for control of Russian wheat aphid.

Survivors of Spilarctia obliqua derived from 3 rd instars that had ingested LC50 of imidacloprid (0.025%), dichlorvos (0.014%) and endosulfan (0.012%) were studied through the life table method. Survivorship was reduced in insecticide exposed populations as compared to 45-day in the control groups. Egg hatching was significantly decreased for the insecticide treated populations. Total larval mortality was the highest for endosulfan (36.76%) as compared to the individuals that died among control groups (14.29%). Life expectancy (ex) was decreased gradually over time and stage of development for insecticides tested and the control groups. Dichlorvos (0.014%) has caused a significant reduction in the potential fecundity i.e. 315 females/female/generation, while 415 in the unexposed cohorts. Net reproductive rate (Ro) was the lowest in endosulfan (118.47 females/female/ generation) treatment followed by dichlorvos (141.97), imidacloprid (144.49) and the control groups (272.42). Similarly, the intrinsic rate of increase (rm) was substantially decreased after exposure with endosulfan (0.124 females/female/day) as compared to 0.135 in the unexposed cohort. The finite rate of increase (l) was not significantly different among the insecticide treatments and control groups. Mean generation time was significantly reduced after exposure to dichlorvos (37.19 days). However, 41.34 days were required to complete one generation by S. obliqua in the absence of insecticides. Based on these results, population of S. obliqua would double in 5.19 days under the influence of dichlorvos while requiring 5.13 days for unexposed cohorts.

The assemblages of microbial (bacteria and fungi), microfaunal (protozoa and nematodes) and mesofaunal (microarthropods) populations were studied in decomposing root residues from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) in a litterbag field experiment. Litterbags containing vetch or rye root residues were buried in soil at the same day as either vetch or rye winter catch crops were incorporated into the field soil from which the materials were gathered. The litterbags were sampled after 6 weeks in the field. In vetch, bacterial and fungal biomasses were similar whereas fungi dominated microbial biomass in rye. The biomass of the bacterial consuming fauna dominated by nematodes and microarthropods was similar to the biomass of bacteria in vetch as opposed to in rye where bacterivore biomass was lower than bacterial biomass. This suggests a much higher bacterial production in vetch compared to rye. Furthermore, in vetch dauer larvae of bacteria feeding nematodes prevailed, which is also a sign of high bacterial production followed by food shortage for the bacterivores. Bacterivorous and predatory nematodes with capability of consuming protozoa showed an inverse relationship to flagellated protozoa. This suggests that these nematodes controlled the protozoan biomass constituting a lower fraction of the bacterivore biomass in vetch compared to in rye. Such intraguild predator-prey relationship is therefore indicated for microbivorous organisms among bacterivorous and predatory nematodes (the intraguild predator) protozoa (the intraguild prey) and bacteria (the common prey). The much higher fungal biomass in rye than in vetch litterbags was not reflected in the biomass of the fungal feeders. Due to the generally lower intrinsic rate of increase of the fungivores, as well as of the omnivores and predators, in comparison with the bacterial feeders, they were not able to generate dense populations at this early stage of decomposition. q

The fast-growing Central American tree Leucaena leucocephala (Lam.) de Wit (Leguminosae: Mimosoidaeae) has been widely planted in the tropics since the 1970s for agro-forestry, reforestation, and fodder. Since the mid-1980s the tree has suffered serious damage throughout its exotic range from the psyllid Heteropsylla cubana Crawford, which is also native to Central America. This article summarizes Þeld studies on the tree and the psyllid conducted at 2 sites in north Thailand: a cool highland and a warm valley site. In the highlands, mean psyllid densities per shoot were slightly higher, defoliation was greater, and dry matter production losses due to the psyllid were Ͼ3 times higher than those at the valley site (62.5 and 18.3% losses, respectively). Using Þeld data, the lower thermal thresholds for tree growth and psyllid development were 11.2 and 9.6ЊC, respectively. Psyllid abundance was negatively correlated to temperature. When maximum temperatures exceeded 36ЊC, psyllid abundance fell dramatically, mortality increased, and body size decreased. These data suggest that the tree and the psyllid are climatically mismatched. H. cubana prefers new shoots, and population cycles were related to tree growth cycles. Finally, populations of the introduced parasitoid Psyllaephagus yaseeni Noyes (Hymenoptera: Encyrtidae), native coccinellids, and spiders showed little correlation to the psyllid populationÕs intrinsic rate of increase. Percentages of parasitism by P. yaseeni were low (mean ϭ 1.2Ð1.9%, maximum ϭ 6.0%) and no evidence of density dependent regulation was found.

Estimating the population consumption of an insect population under elevated CO 2 is an important step in understanding the effects of elevated CO 2 on herbivore-crop interactions. Two successive generations of cotton bollworm, Helicoverpa armigera Hü bner, were reared on milky grains of spring wheat (Triticum aestivum L.) grown in open-top chambers under increased carbon dioxide (CO 2) concentration. H. armigera development, wheat consumption, and parasitism by Microplitis mediator Haliday were examined, as were the effects of elevated CO 2 on the wheat itself. We experimentally tested the hypotheses that, by quantifying the population consumption of H. armigera, elevated CO 2 enhanced the pest-control ability of M. mediator again H. armigera. Decreases in protein, total amino acid, and nitrogen (N) content were noted in spring wheat when grown in an elevated-CO 2 environment, as were increases in total non-structure carbohydrates (TNCs) and in the ratio of TNC to N. In the first generation of H. armigera reared under elevated CO 2 , no significant changes were observed in population generation time (T) or in the intrinsic rate of increase (r m) between CO 2 treatments. However, in the second treatment generation, longer generation time resulted in a lower r m value. Elevated-CO 2 levels caused no significant changes in the H. armigera population's total wheat consumption. The rates of parasitism, cocooning, and emergence by M. mediator were also unaffected, as were its average weight and adult lifespan. As no significant changes in wheat consumption by H. armigera or in the parasitic rate of M. mediator were revealed, the results indicate that the population relationship between H. armigera and M. mediator is unlikely to vary due to future elevated atmospheric CO 2 concentrations.

Disease progress curves were evaluated for the assessment of the susceptibility of the flora of the South-West Botanical Province of Western Australia threatened by Phytophthora cinnamomi infection. Disease progress was analysed with the logistic model because this model describes numerous observed disease progress curves. In addition, the three logistic model parameters, upper asymptote (Kmax), lag time (t1/2K) and intrinsic rate of increase (r), have rational physical interpretations. Because the logistic model parameters for percentage of plants with collar lesions were significantly related to parameters for percentage mortality, only the logistic model parameters for percentage mortality were used in subsequent analysis. Susceptible hosts had the greatest Kmax, shortest t1/2K and fastest r. These parameters change to lowest Kmax, longest t1/2K and slowest r for resistant plant taxa. There was a greater change of Kmax with t1/2K than with r. The Kmax and r parameters did not differ significantly between isolates of the pathogen. Variation in mortality curve parameters between years was greater for Banksia grandis than for the more susceptible B. brownii. There was no significant linear relationship between mortality curve parameters for B. brownii and temperature variables. For B. grandis there were four significant linear relationships between a mortality curve parameter and a temperature variable. Potting mix soil favoured greatest disease progress with the shortest t1/2K and fastest r. Susceptibility to P. cinnamomi determined in a shadehouse environment following soil inoculation was significantly positively correlated with susceptibility recorded in disease centres in natural environments.

Habitat suitability for P. cinnamomi was compared between soils from the major soil groups of the Fitzgerald River National Park. Because of the mainly disease-free status of the National Park, only ex-situ testing was possible by Gradsect sampling of soils on a topographic gradient and determining the influence on disease expression in a shadehouse environment and stimulation of sporangium production in a controlled environment. The upper asymptote (K max ), lag time (t ½K ) and intrinsic rate of increase (r) of the logistic model were calculated from disease progress curves of Banksia baxteri plants following soil inoculation with P. cinnamomi and sporulation curves. The Qualinup Sands and the Dry Phase of the Nyerilup Sand had the greatest % mortality K max values and the Perkins and Red Loams had the least. For B. baxteri mortality, delay significantly increased and rate decreased along a fertility gradient from relatively infertile sands to fertile loams. K max of total number of sporangia/mm 2 of mycelium for winter collected soils was significantly linearly positively correlated with K max of germinating spores/disc and negatively correlated with rate of mortality of B. baxteri. The loams with the slowest rate of mortality of B. baxteri stimulated the most sporulation. Habitat suitability of the major soil groups of the landscape matrix of the Fitzgerald River National Park for P. cinnamomi can be used to predict risk of invasion and hazard in healthy areas and prioritise areas of greatest risk of invasion and conservation consequences from hazard.

The effect of different cole crops was studied on biological parameters of Pieris brassicae (L.) in the laboratory at 28 ˚C, 65% RH, and 12L:12D photoperiod. The results indicated that host plants significantly affected the life history , i.e. survival of developmental stages, oviposition period, and sex ratio of P. brassicae. Comparative study on different host plant revealed that P. brassicae required a maximum of 40 days to complete generation on cabbage, cauliflower, and broccoli. The survivorship and expectation of life declined gradually with the advancement of age; the life expectancy of newly deposited eggs was 23.96 days while it was 8.12 days at the time of adult emergence on cabbage. However, the fluctuations of mortality parameter were seen on all the cole crops. On cabbage, 100% hatching of eggs with low larval mortality were noticed. The highest net reproductive rate (R0) occurred on cauliflower, i.e. 27.1 followed by cabbage 24.89, females per female per generation. Intrinsic rate of increase (rm), was found to be highest (0.09558954) on cauliflower followed by broccoli and cabbage, 0.078886 and 0.077551 females per female per day, respectively. The smallest rm (0.059469 females per female per day) occurred on radish which shows that P. brassicae did not perform well on radish. In addition, P. brassicae may double in 7.2 days on cauliflower, 8.7 days on broccoli, and 8.9 days on cabbage. The sex ratio was computed as 1.5:1, female:male, respectively on cabbage.

We have studied reciprocal transplant gardens involving the hybrid zone between basin and mountain big sagebrush ( Artemisia tridentata ) in Salt Creek Canyon, Utah, for 9 years. Previously, we showed that the parental taxa and hybrids had superior reproductive and vegetative performance in their native garden. These earlier data supported the Bounded Hybrid Superiority model. Now, after 9 years, we find that the mountain seed source plants have greater relative fitness than middle hybrid zone seed source plants in the middle hybrid zone garden. These results may be due to plant density and climatic factors more conducive to mountain seed source growth than that of either basin or middle hybrid zone seed source plants. On the other hand, these fitness estimates do not take into account the timing of reproduction, which together with the age-specific survival rate, can profoundly affect lifetime fitness. The intrinsic rate of increase ( r ) takes both of these factors into account, providing another estimate of fitness. Middle hybrid zone seed source plants had the greatest rate of increase in both the middle hybrid zone and mountain gardens and a greater rate of increase than either parent in the basin garden. This is most likely due to the greater reproductive performance of middle hybrid zone plants earlier in life than either parental taxon. These results partly support the Bounded Hybrid Superiority model and show the importance of long-term studies of hybrid fitness.

The performance of three clonal lineages of Aphis gossypii Glover originating from central Greece was studied on six commercial cotton cultivars that differ with respect to leaf pubescence traits (Zeta-2, Zeta-5, Eva, Korina, Acala-SJ2 and Sindos-80). Two main laboratory experiments were conducted: (i) one clonal lineage was studied on all six varieties; and (ii) four varieties were assayed with two other lineages. Aphid development, fecundity, longevity and mortality were recorded and life-table characteristics estimated for all varieties. The results showed that leaf trichome density was significantly correlated with aphid performance (i.e. positive correlation with intrinsic rate of increase and fecundity, and negative correlation with developmental time) in both experiments. Leaf hairiness was at least partly responsible for the poorer performance in cotton aphid lineages. We hypothesise that other factors such as allelochemicals (e.g., gossypol, tannins), which are known to affect hemipteran insects, also might be involved.

‘Superclones’ are predominant and time-persistent genotypes, exhibiting constant fitness across different environments. However, causes of this ecological success are still unknown. Therefore, we studied the physiological mechanisms that could explain this success, evaluating the effects of wheat chemical defences on detoxification enzymes [cytochrome P450 monooxygenases (P450), glutathione S-transferases (GST), esterases (EST)], standard metabolic rate (SMR), and fitness-related traits [adult body mass and intrinsic rate of increase (rm)] of two ‘superclones’ (Sa1 and Sa2) of the grain aphid, Sitobion avenae. Additionally, we compared ‘superclones’ with a less-frequent genotype (Sa46). Genotypes were reared on three wheat cultivars with different levels of hydroxamic acids (Hx; wheat chemical defences). Detoxification enzymes and SMR did not differ between wheat hosts. However, GST and EST were different between ‘superclones’ and Sa46, while Sa1 showed a higher SMR than Sa2 or Sa46 (p = 0.03). Differences between genotypes were found for rm, which was higher for Sa1 than for Sa2 or Sa46. For all cases, genotype–host interactions were non-significant, except for aphid body mass. In conclusion, ‘superclones’ exhibit a broad host range, flat energetic costs for non-induced detoxification enzymes, and low variation in their reproductive performance on different defended hosts. However, physiological specialization of ‘superclones’ that could explain their ecological success was not evident in this study.