Lifetime Reproductive Success in the Solitary Endoparasitoid, Venturia canescens

Parasitoid wasps have long been considered excellent organisms in studies examining the evolution of reproductive and life-history strategies. In examining the lifetime reproductive success of parasitoids in the laboratory, most investigations have provided the insects with excess hosts and food, where they exist in a relatively constraint-free environment. Importantly, these conditions may not accurately reflect the true heterogeneity of natural systems, where suitable hosts and food sources are likely to be limiting. This study examines the influence of differences in host and food availability on reproductive and life-history parameters in an asexual strain of the solitary endoparasitoid, Venturia canescens (Hymenoptera: Ichneumonidae). Lifetime reproductive success in V. canescens was measured in response to temporal variations in host and food (honey solution) access. Cohorts of parasitoids were provided with 200 fifth-instar larvae of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae), and food for variable periods daily after eclosion. V. canescens is synovigenic, and host-deprived wasps continued to mature eggs over the first few days after eclosion until the egg storage capacity was reached in the oviducts. When these wasps were subsequently provided with hosts, oogenesis resumed and continued until later in adult life. Constantly fed wasps lived longer and produced more progeny than wasps from cohorts which were alternately fed and starved or were starved from eclosion. Moreover, wasps with constant host and food access produced most progeny early in life and usually experienced prolonged periods of postreproductive survival. In contrast, the reproductive period of wasps with limited host access was more evenly distributed throughout the adult life. Consequently, the cumulative progeny production by V. canescens with constant food access was fairly uniform irrespective of host availability. Longevity and fecundity in V. canescens were positively correlated with adult size. However, variable host access had little effect on the longevity of wasps which were constantly supplied with honey. Over the first 2 days of adult life, variation in food access also had no effect on progeny production by V. canescens. We argue that manipulating temporal host and food access to parasitoids in the laboratory more closely approximates natural conditions, where these resources are likely to be spatially separated. Moreover, our findings suggest that many highly synovigenic parasitoids like V. canescens, which produce microtype (=hydropic) eggs, have a considerably higher reproductive potential than ovary dissections have revealed. Our findings are discussed in relation to life-history evolution in the parasitic Hymenoptera.     

Is fatter fitter? Body storage and reproduction in ten populations of the freshwater amphipod Gammarus minus

Relationships between body storage (estimated as fat content and residuals of body mass regressed against body length) and offspring investment [brood mass, brood size (number of embryos per brood) and embryo mass] were examined within and among populations of the amphipod Gammarus minus in ten cold springs in central Pennsylvania, USA. Two major hypotheses and six corollary hypotheses were tested. Total reproductive investment (brood mass and brood size) was usually strongly positively correlated with maternal body length and body storage both within and among populations. These positive associations between reproductive and somatic investments are expected if individual variation in resource acquisition exceeds that of resource allocation. That is, individuals or populations that are able to acquire more resources should also be able to allocate more resources to both reproduction and somatic reserves than those acquiring fewer resources. This hypothesis is consistent with evidence showing that individual differences in body storage in G. minus and other amphipods are related to differences in resource acquisition. Positive associations between reproductive and somatic investments do not mean that energy costs of reproduction do not exist in G. minus. Evidence for reproductive energy costs included the lower body-fat contents of brooding versus nonbrooding females and the relatively low body mass per length of females who had just deposited eggs in their brood pouch. Unlike brood mass and brood size, individual embryo mass was usually unrelated to maternal body length and body storage. This pattern is largely consistent with optimal offspring investment theory, which predicts that offspring size should be insensitive to variation in parental resource status. However, in contrast to theory, embryo mass increased in winter when brooding females were significantly ”fatter”, presumably due to the availability of autumn-shed leaf food. This seasonal change in offspring size may be a maternally mediated effect of increased resource availability, though other explanations are possible. Overall, this study suggests that ”fatter” female amphipods are fitter than ”thinner” ones, though both the costs and benefits of increased body storage and brood size require investigation to substantiate this claim. This study also suggests that effects of individual variation in resource acquisition on life-history patterns deserve more theoretical and empirical attention by ecologists than they have received. It should be recognized that positive and/or nonsignificant correlations between life-history traits are just as interesting and important as are the negative correlations predicted by many theoretical models. Received: 20 January 1999 / Accepted: 26 September 1999     

The role of food quality and competition in shaping the seasonal cycle in the reproductive activity of the sycamore aphid

The hypothesis that seasonal changes in sycamore aphid,Drepanosiphum platanoidis (Schr.), recruitment are determined by changes in food quality and aphid population density was tested. There was no clear association between the reproductive activity of the sycamore aphid and the seasonal changes in specific amino acids or groups of amino acids in extracts of sycamore,Acer pseudoplatanus L., leaves. Seasonal changes in reproductive activity tracked the changes in total amino acids of the leaf tissue of the host, but with a short time delay. High numbers of adult aphids appeared to depress reproductive activity. A regression analysis of the results revealed that total amino acids the previous week and current numbers of adult aphids significantly affected sycamore aphid reproductive activity. The results of this analysis support the above hypothesis, that the marked seasonal changes in the total quantity of amino acids in sycamore leaves and intraspecific competition for this resource, through its effect on adult weight, shape the seasonal cycle in the reproductive activity of the sycamore aphid.     

Physiological responses of Uroleucon jaceae (L.) to seasonal changes in the quality of its host plant Centaurea jacea L.: multilevel control of adaptations to the life cycle of the host

Summary Exploiters of short-lived plants have evolved strategies in response to physiological changes that occur during the development of their hosts. The ability to adapt to host quality changes is necessary particularly if the mobility of an animal is poor or risk-constrained. In the plant-aphid system Centaurea jaceae-Uroleucon jaceae, the responses of the aphid to the seasonal changes in its host plant grown in poor and good quality soil were investigated. Coarse- and fine-tuned physiological reactions were observed in discrete aphid generations which were reared on plants grown either in a growth chamber or in a greenhouse. The number of ovarioles and developmental time depended on extrinsic factors (length of photoperiod) not directly related to plant quality. The reproductive investment of the aphids was also independent of their total dry weight. However, within the gonadal system high correlations were found at the embryonic level (e.g. the number of sclerotized embryos or the length of the oldest embryos per ovariole were highly correlated with gonadal dry weight). Aphids which were living on the 4-leaf stage of high-quality host plants showed a significantly higher investment in their gonads than aphids feeding on senescenting hosts. Factor analysis corroborated that aphids reared on poor-quality hosts revealed no grouping of variables measured, whereas those which were reared on high-quality plants showed clustering in respect of somatic (tibia length, dry weight of soma) and gonadal (number of sclerotized and unsclerotized embryos, length of the oldest embryos, ovariole number, gonad dry weight) factors. Three different levels of adaptive response to plant quality are distinguished: individual response to host quality, maternal influences on offspring and response to changes not specific to habitat (photoperiod). These different levels of regulation are thought to enable the aphids to adapt to a host of a given nutritional quality and anticipate deteriorating habitat quality simultaneously. It is concluded that physiological constraints in aphids are only revealed when aphids are exposed to severe nutritional stress for several generations.     

三种同域分布喉毛花的繁殖分配

以青藏高原高寒草甸中三种同域分布的喉毛花为研究对象,通过比较三个种的植株性状和繁殖分配,探讨繁殖分配的种间差异及其与植株个体大小的关系。结果表明:(1)三个种的植株高度、顶花大小和单株花数目、繁殖分配均存在种间差异,这可能与其各自的交配系统和具体的生境以及相应的生活史对策有关;(2)在三种喉毛花中,投入到营养器官和繁殖器官的绝对资源量均呈显著正相关,未检测到植株生长和繁殖间的权衡关系;(3)三个种的个体大小与繁殖器官生物量均呈显著正相关,而与繁殖分配均呈显著负相关,这表明个体越大,繁殖投入越高,而繁殖分配越低,与以往研究结果一致,这可能是由于繁殖分配与个体大小之间存在异速关系。     

Female Oviposition Decisions and Their Impact on Progeny Life-History Traits

An important factor affecting the life-history of an organism is parental investment in reproduction: reproductive decisions are almost invariably costly. Therefore, reproductive decisions should be beneficial in terms of increased offspring number or fitness. For example, egg laying decisions in many insects can influence resource availability of the offspring through changes in the larval density, and resource availability will have effects on many life-history traits. Here we studied whether female reproductive decisions affect offspring fitness in Callosobruchus maculatus seed beetles. Females laid more eggs on black-eye beans than on mung beans. However, when the difference in the surface area of the beans was accounted for, the number of eggs was not higher in black-eye beans. This together with the poisson distribution of eggs on each of the bean types suggests that females tend to lay their eggs randomly. We found that development time was longer, larval mortality lower and adult survival higher in black-eye beans. We also found interactions between bean type and larval density on size of the offspring such that in mung beans the emergence mass and pronotum width decreased with increasing larval density, but in black-eye beans larval density did not affect the size measures. We conclude that when there is a risk that larval denisty will become high within a bean and there is variable resources available, there exist clear benefits that females might obtain by choosing black-eye beans as a resource for their offspring. However, in contrast to many earlier studies, our results suggest that females may not be making any active oviposition decisions. Therefore, to unequivocally determine whether females do capitalise the potential benefits by active decision making, some further experimentation is required.     

青藏高原不同生境下湿生扁蕾(Gentianopsis paludosa)个体大小依赖的繁殖分配

植物对资源的投资和分配是生态学中的重要问题,它反映了植物应对环境变化时的生活史策略。选择青藏高原东缘同一海拔下的嵩草草甸(Kobresia sp.meadow)、金露梅灌丛(Potentilla fruticosa shrub meadow)以及草甸-灌丛交错带3种生境类型,并以3种生境下的湿生扁蕾(Gentianopsis paludosa)为对象,研究了其繁殖分配特征。结果发现:(1)在种群水平上,在生境从草甸经交错带到灌丛的变化中,湿生扁蕾个体大小和繁殖分配比例逐渐增加;3个种群湿生扁蕾的总花数目没有显著差异,但草甸生境湿生扁蕾的蕾期花数目显著高于灌丛生境,而果期花数目则显著低于灌丛生境;(2)在个体水平上,湿生扁蕾的繁殖绝对投入与个体大小显著正相关,且各种群植株都存在繁殖所需的个体大小阈值,而繁殖阈值在生境从草甸经交错带到灌丛的过渡中逐渐减小;湿生扁蕾的繁殖相对投入与个体大小负相关,但相关系数随着生境从草甸经交错带到灌丛的过渡中逐渐减小;各种群花数目与湿生扁蕾植株个体大小显著正相关。研究表明,湿生扁蕾的繁殖投资存在大小依赖效应,但生境差异会对其繁殖投资和生活史策略造成显著影响,而这种影响主要是由不同生境下自然条件的不同造成的。同时,资源分配也与湿生扁蕾的遗传特性和延迟自交的繁育系统特征有关。湿生扁蕾这种不同生境下个体大小依赖的繁殖投资差异是湿生扁蕾与其生境长期适应和进化(生境选择)的结果。     

Food supply modifies the trade-off between past and future reproduction in a sexual parasite–host system (<Emphasis Type="Italic">Rana esculenta,Rana lessonae</Emphasis>)

Life history theory is concerned with the costs of survival, growth and reproduction under different ecological conditions and the allocation of resources to meet these costs. Typical approaches used to address these topics include manipulation of food resources, followed by measures of subsequent reproductive traits, and measures of the relationship between current and future reproductive investment. Rarely, however, do studies test for the interaction of past investment, present resource availability and future investment simultaneously. Here, we investigate this interaction in females of a sexual parasite–host system consisting of the hybridogenetic frog Rana esculenta (E) and one of its parental species Rana lessonae (L). We kept females from each of two groups (with or without previous reproduction) under two food treatments (low or high) and regularly recorded their growth as well as their body condition and hormone titres as measures of future reproductive condition. After keeping them in hibernation until the following spring, we exposed the females to males, recorded whether they spawned or not and related this response to their condition in the previous autumn. Past reproduction negatively affected growth during summer and condition during autumn which, in turn, reduced the following year’s reproductive output. These costs of previous reproduction were less pronounced under the high than under the low food treatment and lower in R. lessonae than in R. esculenta. Increasing food supply improved reproductive condition more in L than in E females. These species differences in reproductive costs and food requirements provide a mechanistic explanation for why E females skip annual reproduction almost twice as often as L females. Since R. esculenta is a sexual parasite that depends on R. lessonae for successful reproduction, these species-specific life history patterns not only affect individual fitness but also the spatial structure and temporal dynamics of mixed LE populations.     

Effects of parasitic castration on plant resource allocation

It has been proposed that host castration is a parasite strategy to reallocate host resources from reproductive to vegetative functions to increase parasite fitness. Since resource partitioning between reproduction and vegetative growth can affect host life-history traits, parasite effects on resource allocation can affect both plant fitness and host-parasite coevolution. Field and greenhouse experiments were used to investigate the effects of host castration by the fungus Atkinsonella hypoxylon on the resource allocation and architecture of the grass Danthonia spicata. The results indicate that non-infected D. spicata can reallocate resources from reproduction to vegetative growth when resource allocation to reproduction is prevented. However, I found no evidence that fungal castration causes reallocation of resources from host reproduction to vegetative growth. Instead, infection reduces host biomass and the fungus directly utilizes resources that would have been used for host reproduction for its own reproduction. Received: 25 March 1999 / Accepted: 24 October 1999     

Complex trait differentiation between host-populations of the pea aphid Acyrthosiphon pisum (Harris): implications for the evolution of ecological specialisation

Variation in traits affecting preference for, and performance on, new habitats is a key factor in the initiation of ecological specialisation and adaptive speciation. However, habitat and resource use also involves other traits whose influence on ecological and genetic divergence remains poorly understood. In the present study, we investigated the extent of variation of life-history traits among sympatric populations of the pea aphid Acyrthosiphon pisum , which shows several host races that are specialised on various plants of the family Fabaceae plants and is an established model for ecological speciation. First, we assessed the community structure of microbial partners within host populations of the pea aphid. The effect of these microbes on host fitness is uncertain, although there is growing evidence that they may modulate various important adaptive traits of their host such as plant utilisation and resistance against natural enemies. Second, we performed a multivariate analysis on several ecologically relevant features of host populations recorded in the present and previous studies (including microbial composition, colour morph, reproductive mode, and male dispersal phenotype), enabling the identification of correlations between phenotypic traits. We discuss the ecological significance of these associations of traits in relation to the habitat characteristics of pea aphid populations, and their consequences for the evolution of ecological specialisation and sympatric speciation.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 718–727.     

Female production within the gall and male production on leaves by individual alates of a social aphid

The social aphid Astegopteryx spinocephala forms a banana-bunch shaped gall, consisting of several subgalls, on Styrax benzoides in northern Thailand. The aphid’s life cycle is non-host alternating. Alates (sexuparae) containing both male and female embryos appear near the end of the dry season, when many sexuals and eggs are found in subgalls guarded by sterile soldiers. Our experiments revealed that these alates give birth to almost all (99%) females within the natal subgall before flying but most (73–86%) males on leaves of the host tree after flying, and that these first-instar males intrude into live subgalls for mating. The fact that some (14–27%) males are deposited in the natal subgall indicates the occurrence of both outbreeding and inbreeding, or some level of local mate competition (LMC), in this mating system. However, the primary (investment) sex ratio was estimated to be near 0.5. This suggests that factors other than LMC, a candidate for which is local resource competition, might also affect the sex ratio in A. spinocephala. Received 19 March 2007; revised 12 July 2007; accepted 13 August 2007.     

Evolutionary history of aphid-plant associations and their role in aphid diversification

Aphids are intimately linked with their host plants that constitute their only food resource and habitat, and thus impose considerable selective pressure on their evolution. It is therefore commonly assumed that host plants have greatly influenced the diversification of aphids. Here, we review what is known about the role of host plant association on aphid speciation by examining both macroevolutionary and population-level studies. Phylogenetic studies conducted at different taxonomic levels show that, as in many phytophagous insect groups, the radiation of angiosperms has probably favoured the major Tertiary diversification of aphids. These studies also highlight many aphid lineages constrained to sets of related host plants, suggesting strong evolutionary commitment in aphids’ host plant choice, but they fail to document cospeciation events between aphid and host lineages. Instead, phylogenies of several aphid genera reveal that divergence events are often accompanied by host shifts, and suggest, without constituting a formal demonstration, that aphid speciation could be a consequence of adaptation to new hosts. Experimental and field studies below the species level support reproductive isolation between host races as partly due to divergent selection by their host plants. Selected traits are mainly feeding performances and life cycle adaptations to plant phenology. Combined with behavioural preference for favourable host species, these divergent adaptations can induce pre- and post-zygotic barriers between host-specialized aphid populations. However, the hypothesis of host-driven speciation is seldom tested formally and must be weighed against overlooked explanations involving geographic isolation and non-ecological reproductive barriers in the process of speciation.     

Separate and combined effects of nutrition during juvenile and sexual development on female life-history trajectories: the thrifty phenotype in a cockroach

We have yet to understand fully how conditions during different periods of development interact to influence life-history structure. Can the negative effects of poor juvenile nutrition be overcome by a good adult diet, or are life-history strategies set by early experience? Here, we tested the influence and interaction of different nutritional quality during juvenile and sexual development on female resource allocation physiology, life history and courtship behaviour in the cockroach, Nauphoeta cinerea. Nymphs were raised on either a good-quality or poor-quality diet. After adult eclosion, females were either switched to the opposite diet or remained on their original diet. We assessed mating behaviour and lifetime reproductive success for half of the females from each treatment. We evaluated reproductive investment, somatic investment and resource reallocation from reproduction to the soma via oocyte apoptosis in the remaining females. We found that poor juvenile conditions resulted in a fat phenotype with slow juvenile growth and short reproductive lifespan that could not be retrieved with a change in diet. Good juvenile conditions resulted in the converse, but again fixed, phenotype in adulthood. Thus, juvenile nutrition sets adult patterns of resource allocation.     

Masting uncoupling: mast seeding does not follow all mast flowering episodes in a dioecious juniper tree

Evolutionary selective forces, like predator satiation and pollination efficiency, are acknowledged to be major causes of masting (the variable, periodic and synchronic production of seeds in a population). However, a number of recent studies indicate that resources might also play an important role on shaping masting patterns. Dioecious masting species offer a privileged framework to study the role of resources on masting variation, since male and female plants often experience different reproductive costs and selective pressures. We followed masting and reproductive investment (RI) of the dioecious tree Juniperus thurifera in two populations along 10 years and studied the different response of males and females to experimentally increased water and nutrient availability in a third population. Juniperus thurifera females invested in reproduction three times more resources than males. Such disparity generated different resource‐use strategies in male and female trees. Tree‐ring growth and water use efficiency (WUE) confirmed that sexes differed in their resource investment temporal pattern, with males using current resources for reproduction and females using resources accumulated during longer periods. Watered and fertilized female trees presented significantly higher flowering reproductive investments than males and experienced an extraordinary mast‐flowering event. However, seeding RI and mast seeding were not affected by the treatment. This suggests that although resource availability affects the reproductive output of this species, there are other major forces regulating masting on J. thurifera. During 10 years, J. thurifera male and female trees presented high and low flowering years more or less synchronously. However, not all mast flowering episodes resulted in mast seeding, leading to masting uncoupling between flowering and seeding. Since flowering costs represent only 1% of females’ total reproductive investments, masting uncoupling could be a beneficial bet‐hedging strategy to maximize reproductive output in spite of unpredictable catastrophic events.     

Phenotypic plasticity in adult life-history strategies compensates for a poor start in life in Trinidadian guppies (Poecilia reticulata)

Low food availability during early growth and development can have long-term negative consequences for reproductive success. Phenotypic plasticity in adult life-history decisions may help to mitigate these potential costs, yet adult life-history responses to juvenile food conditions remain largely unexplored. I used a food-manipulation experiment with female Trinidadian guppies (Poecilia reticulata) to examine age-related changes in adult life-history responses to early food conditions, whether these responses varied across different adult food conditions, and how these responses affected overall reproductive success. Guppy females reared on low food as juveniles matured at a later age, at a smaller size, and with less energy reserves than females reared on high food as juveniles. In response to this setback, they changed their investment in growth, reproduction, and fat storage throughout the adult stage such that they were able to catch up in body size, increase their reproductive output, and restore their energy reserves to levels comparable to those of females reared on high food as juveniles. The net effect was that adult female guppies did not merely mitigate but surprisingly were able to fully compensate for the potential long-term negative effects of poor juvenile food conditions on reproductive success.     

Genetic variation in the effect of a facultative symbiont on host-plant use by pea aphids

Ecological specialisation on different host plants occurs frequently among phytophagous insects and is normally assumed to have a genetic basis. However, insects often carry microbial symbionts, which may play a role in the evolution of specialisation. The bacterium Regiella insecticola is a facultative symbiont of pea aphids (Acyrthosiphon pisum) where it is found most frequently in aphid clones feeding on Trifolium giving rise to the hypothesis that it may improve aphid performance on this plant. A study in which R. insecticola was eliminated from a single naturally infected aphid clone supported the hypothesis, but a second involving two aphid clones did not find the same effect. We created a series of new pea aphid–R. insecticola associations by injecting different strains of bacteria into five aphid clones uninfected by symbionts. For all aphid clones, the bacteria decreased the rate at which aphids accepted Vicia faba as a food plant and reduced performance on this plant. Their effect on aphids given Trifolium pratense was more complex: R. insecticola negatively affected acceptance by all aphid clones, had no effect on the performance of four aphid clones, but increased performance of a fifth, thus demonstrating genetic variation in the effect of R. insecticola on pea aphid host use. We discuss how these results may explain the distribution and frequency of this symbiont across different aphid populations. Julia Ferrari and Claire L. Scarborough contributed equally to the work.     

Reproductive diapause and the bacterial symbiosis in the sycamore aphid Drepanosiphum platanoidis

1. Parthenogenetic adults of the sycamore aphid Drepanosiphum platanoidis exhibited reproductive diapause for 4–6 weeks in the summer. 2. The diapausing aphids had small gonads (accounting for just 13% of the total aphid protein content) bearing small (< 0.5 mm long) and developmentally immature embryos. There was no evidence of embryo resorption. 3. The diapausing aphids had significantly depressed essential amino acid content and elevated glutamine content, relative to reproductively active D. platanoidis. 4. The reproductive characteristics and amino acid titres of the diapausing aphids resemble those of aphids lacking functional symbiotic bacteria. Uncoupling of maternal and embryo growth and suppression of bacterial function are proposed as key elements in the diapause of D. platanoidis.     

The effect of maternal and paternal immune challenge on offspring immunity and reproduction in a cricket

Trans‐generational immune priming is the transmission of enhanced immunity to offspring following a parental immune challenge. Although within‐generation increased investment into immunity demonstrates clear costs on reproductive investment in a number of taxa, the potential for immune priming to impact on offspring reproductive investment has not been thoroughly investigated. We explored the reproductive costs of immune priming in a field cricket, Teleogryllus oceanicus. To assess the relative importance of maternal and paternal immune status, mothers and fathers were immune‐challenged with live bacteria or a control solution and assigned to one of four treatments in which one parent, neither or both parents were immune‐challenged. Families of offspring were reared to adulthood under a food‐restricted diet, and approximately 10 offspring in each family were assayed for two measures of immunocompetence. We additionally quantified offspring reproductive investment using sperm viability for males and ovary mass for females. We demonstrate that parental immune challenge has significant consequences for the immunocompetence and, in turn, reproductive investment of their male offspring. A complex interaction between maternal and paternal immune status increased the antibacterial immune response of male offspring. This increased immune response was associated with a reduction in son's sperm viability, implicating a trans‐generational resource trade‐off between investment into immunocompetence and reproduction. Our data also show that these costs are sexually dimorphic, as daughters did not demonstrate a similar increase in immunity, despite showing a reduction in ovary mass.     

The effects of reproductive specialization on energy costs and fitness genetic variances in cyclical and obligate parthenogenetic aphids

Organisms with coexisting sexual and asexual populations are ideal models for studying the consequences of either reproductive mode on the quantitative genetic architecture of life-history traits. In the aphid Rhopalosiphum padi, lineages differing in their sex investment coexist but all share a common parthenogenetic phase. Here, we studied multiple genotypes of R. padi specialized either for sexual and asexual reproduction and compared their genetic variation in fitness during the parthenogenetic phase. Specifically, we estimated maintenance costs as standard metabolic rate (SMR), together with fitness (measured as the intrinsic rate of increase and the net reproductive rate). We found that genetic variation (in terms of broad-sense heritability) in fitness was higher in asexual genotypes compared with sexual genotypes. Also, we found that asexual genotypes exhibited several positive genetic correlations indicating that body mass, whole-animal SMR, and apterous individuals production are contributing to fitness. Hence, it appears that in asexual genotypes, energy is fully allocated to maximize the production of parthenogenetic individuals, the simplest possible form of aphid repertoire of life-histories strategies.     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.