Life table studies of the walnut leaf beetle,Gastrolina depressa (Coleoptera: Chrysomelidae), with special attention to aggregation

Summary In order to make clear the relationship between the mortality processes and aggregation on the walnut leaf beetle,Gastrolina depressa, life tables of individual colonies were developed and the major mortality factor and the mode of its action were investigated. Furthermore, the influences of the larval colony size on the survival rate and the developmental period were also investigated in the laboratory. In the laboratory, when the larvae were reared on suitable (soft) host plants, the larger the group size, the faster the development. When the larvae were reared on unsuitable (hard) host plants, the larger the group size, the higher the survival rate. In the field, one of the major mortality factors of the egg stage was physiological death. However, there was no particular relation between the egg mass size and hatchability. On the other hand, another mortality factor of eggs, predation byA. hexaspilota, tended to act more on the larger sized egg masses. The mortality of the 1st instar larvae decreased with the increase of colony size. During the larval stages, the major mortality factor was predation byA. hexaspilota andP. japonica. Both predators tended to attack the colony in an all-or-none manner. The number of male adults was much less than the number of females in the Ina populations.     

Ovipositing female house flies provision offspring larvae with bacterial food

Symbiotic bacteria on house fly eggs, Musca domestica L. (Diptera: Muscidae), provide ovipositional cues for conspecific female flies and curtail the growth of fungi that compete with fly larval offspring for resources. Because bacteria are also essential dietary constituents for developing larvae, we tested the hypothesis that egg‐derived bacteria support development of larvae to adults. From house fly eggs, we isolated and identified 12 strains of bacteria, eight and four of which were previously shown to induce and inhibit oviposition, respectively. When larvae were provisioned with a total dose of 10⁶–10⁷ colony‐forming units of bacteria from either the oviposition‐inducing or inhibiting group, or from both groups together, significantly more larvae completed development. Thus, egg‐associated bacteria could be a fail‐safe mechanism that ensures a bacterial food supply for larval offspring, particularly if the resource selected by parent females is poor in bacterial food.     

Significant mortality of eggs and young larvae of two pine processionary moth species due to the entomopathogenic fungus Metarhizium brunneum

Bioassays were conducted to determine the susceptibility of egg masses and young larvae of two pine processionary moth species, Thaumetopoea pityocampa and Thaumetopoea wilkinsoni, to two strains (ARSEF4556, V275) of the entomopathogenic fungus Metarhizium brunneum. Mortality of treated eggs by both strains ranged from 96% to 99% but not all of this was caused by M. brunneum since control groups also experienced egg mortality due to saprophytic fungi. Still, larvae hatched in the laboratory from eggs treated with M. brunneum were all killed by this fungus, acquiring M. brunneum conidia, whereas larval mortality was 0% in the control groups. Young larvae of both pine processionary moth species were also highly susceptible to ARSEF4556 and V275 with larval mortality ranging between 94% and 100%, 8 days post-inoculation, with the vast majority of larvae being killed within the first 2–4 days. Larval mortality was dose dependent. Results were consistent across the two pine processionary moth species, showing that the pathogenicity of M. brunneum to both eggs and young larvae might be promising for biological control of these insect pests. The study also showed that non-target parasitoids of pine processionary moth eggs were also susceptible to M. brunneum. Further work is required to understand and reduce the M. brunneum effect on non-target insects.     

Interpopulational egg-size variation of a landlocked Rhinogobius goby related to the risk of larval starvation

Reproductive characteristics of a landlocked goby, Rhinogobius sp. (the orange form), in the Lake Biwa water system were compared between the fluvial-lacustrine and lacustrine populations to show the relationship of the egg size to the risk of larval starvation. The comparison of both oocytes in the ovaries and spawned eggs showed that egg size is larger in the fluvial-lacustrine population than in the lacustrine population. Although females of the two populations spawn eggs of the same number as a function of their body size, those of the fluvial-lacustrine population spawn larger eggs even in relation to their body size by investing more in reproduction than those of the lacustrine population. A positive correlation was experimentally shown between the egg size and larval starvation tolerance. Most larvae of the fluvial-lacustrine population (>2 days old) had exhausted their yolk during their larval drift downstream to the lake, indicating that larvae severely suffer from starvation. Egg-size variation between the two populations seemed to be the result of adaptation to the different life cycles, in which the fluvial-lacustrine population confronts the risk of larval starvation, whereas the lacustrine population seems safe from such risk of starvation.     

Evolution of complex life cycles in trophically transmitted helminths. II. How do life‐history stages adapt to their hosts?

We review how trophically transmitted helminths adapt to the special problems associated with successive hosts in complex cycles. In intermediate hosts, larvae typically show growth arrest at larval maturity (GALM). Theoretical models indicate that optimization of size at GALM requires larval mortality rate to increase with time between infection and GALM: low larval growth or paratenicity (no growth) arises from unfavourable growth and mortality rates in the intermediate host and low transmission rates to the definitive host. Reverse conditions favour high GALM size or continuous growth. Some support is found for these predictions. Intermediate host manipulation involves predation suppression (which decreases host vulnerability before the larva can establish in its next host) and predation enhancement (which increases host vulnerability after the larva can establish in its next host). Switches between suppression and enhancement suggest adaptive manipulation. Manipulation conflicts can occur between larvae of different ages/species a host individual. Larvae must usually develop to GALM before becoming infective to the next host, possibly due to trade‐offs, e.g. between growth/survival in the present host and infection ability for the next host. In definitive hosts, if mortality rate is constant, optimal growth before switching to reproduction is set by the growth/morality rate ratio. Rarely, no growth occurs in definitive hosts, predicted (with empirical support) when larval size on infection exceeds growth/mortality rate. Tissue migration patterns and residence sites may be explained by variations in growth/mortality rates between host gut and soma, migration costs and benefits of releasing eggs in the gut.     

The effects of nurse eggs and sibling interactions on the larval development of the poecilogonous annelid Boccardia proboscidea (Spionidae)

In poecilogony, different types of larvae are produced within the same species. Previous studies have suggested maternal control of the production of larval types; however, it is not clear which factors or mechanisms generate contrasting developmental patterns among siblings. The spionid polychaete Boccardia proboscidea produces within the same capsule adelphophagic larvae that eat nurse eggs and siblings and complete all or most of their development inside the capsule (Type A larvae), and larvae with little growth until they hatch as planktotrophic larvae (Type B larvae). In this study, we manipulated capsule content to explore the factors determining larval type in B. proboscidea and the role of extra‐embryonic maternal nutrition and sib–sib interaction in the developmental fate of offspring. When early larval stages were grown individually in vitro, with nurse eggs as the only food source, some of them remained small, while others continue developing into larger pre‐competent larvae by feeding on nurse eggs. This suggests that larval types in B. proboscidea are determined very early in development and are not solely the product of sib–sib interaction inside the capsule. However, our data also suggest that hatching size variability within larval types of a clutch depends on nurse egg availability. Type B larvae grew normally to metamorphosis when phytoplankton was available, but suffered high rates of cannibalism by Type A larvae. These results are consistent with the hypothesis that individual larval fates are determined very early in development and that once their fate is determined, hatching size and intracapsular survival are affected by maternal food provisioning and sibling interaction.     

Group size in a gregarious tortoise beetle: patterns of oviposition vs. larval behaviour

In laboratory and garden experiments, we tested for the existence of adaptive patterns of oviposition and larval behaviour regarding group size in the gregarious tortoise beetle Chelymorpha varians Blanchard (Coleoptera: Chrysomelidae: Cassidinae) on its host plant Calystegia sepium L. (Convolvulaceae). Specifically, we addressed the following questions: (i) Which is the more frequent egg cluster size? (ii) Does cluster size fully predict larval group size? (iii) Are newborn larvae attracted or repelled to conspecific groupings? and (iv) Which is the group size associated with enhanced larval development and adult mass? We found that the mean cluster size was 21.4 eggs. Egg hatch time was significantly shorter in larger clusters. A regression analysis of larval group size against cluster size showed non‐significant results. Thus, original cluster size did not totally determine the larval group size. The mean larval group size was 17.1. Choice tests in an experimental arena showed that larvae clearly preferred leaves of a host plant rather than moistened papers, and that larvae preferred a small group of conspecifics (four larvae per leaf) over larger groups (12 or 20 larvae). Empty leaves of the host plant showed an intermediate level of preference. Development time and beetle performance (adult mass) were affected by larval group size. Larvae in the smallest group (one per leaf) took four more days to attain adulthood than larvae in the larger groups (12 and 20 larvae). Adult C. varians reared in the 12‐larvae group were significantly larger than those reared at the other densities. Comparison of patterns across experimental groups, excluding the 12‐larvae group, showed a tendency for a greater final mass with slower developmental rate.     

Population dynamics of Monochamus carolinensis (Col., Cerambycidae) under laboratory conditions

The study of life history dynamics of the pine sawyer beetle Monochamus carolinensis (Olivier) is of interest because the beetles are vectors for the pinewood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle, the causal agent of pine wilt in susceptible pine trees. Previous observation of a laboratory colony of M. carolinensis suggested numbers of adult beetles reared from logs varied little in relation to oviposition densities among individual logs. Logs in laboratory colonies are routinely subjected to artificially high oviposition rates. The objectives of this study were to examine the relationship between initial oviposition rate, holding time (time between log cut and oviposition), log volume and area and adult survivorship in laboratory colony. This study examined the number of eggs, larvae, adults and generation survivorship in logs over a 2‐year period. The number of adults emerged per log was not related to the number of eggs laid. Late larval and adult numbers were significantly correlated with log size. Only 12% of the initial cohort completed development and emerged as adults. We attribute the high within‐log mortality of beetles to intraspecific competition and cannibalism.     

EVOLUTIONARY LOSS OF LARVAL FEEDING: DEVELOPMENT,FORM AND FUNCTION IN A FACULTATIVELY FEEDING LARVA,BRISASTER LATIFRONS

Species with large eggs and nonfeeding larvae have evolved many times from ancestors with smaller eggs and feeding larvae in numerous groups of aquatic invertebrates and amphibians. This change in reproductive allocation and larval form is often accompanied by dramatic changes in development. Little is known of this transformation because the intermediate form (a facultatively feeding larva) is rare. Knowledge of facultatively feeding larvae may help explain the conditions under which nonfeeding larvae evolve. Two hypotheses concerning the evolutionary loss of larval feeding are as follows: (1) large eggs evolve before modifications in larval development, and (2) the intermediate form (facultatively feeding larva) is evolutionarily short-lived. I show that larvae of a heart urchin, Brisaster latifrons, are capable of feeding but do not require food to complete larval development. Food for larvae appears to have little effect on larval growth and development. The development, form, and suspension feeding mechanism of these larvae are similar to those of obligate-feeding larvae of other echinoids. Feeding rates of Brisaster larvae are similar to cooccurring, obligate-feeding echinoid larvae but are low relative to the large size of Brisaster larvae. The comparison shows that in Brisaster large egg size, independence from larval food, and relatively low feeding rate have evolved before the heterochronies and modified developmental mechanisms common in nonfeeding echinoid larvae. If it is general, the result suggests that hypotheses concerning the origin of nonfeeding larval development should be based on ecological factors that affect natural selection for large eggs, rather than on the evolution of heterochronies and developmental novelties in particular clades. I also discuss alternative hypotheses concerning the evolutionary persistence of facultative larval feeding as a reproductive strategy. These hypotheses could be tested against a phylogenetic hypothesis.     

QUANTIFYING EVOLUTIONARY POTENTIAL OF MARINE FISH LARVAE: HERITABILITY,SELECTION, AND EVOLUTIONARY CONSTRAINTS

For many marine fish, intense larval mortality may provide considerable opportunity for selection, yet much less is known about the evolutionary potential of larval traits. We combined field demographic studies and manipulative experiments to estimate quantitative genetic parameters for both larval size and swimming performance for a natural population of a common coral‐reef fish, the bicolor damselfish (Stegastes partitus). We also examined selection on larval size by synthesizing information from published estimates of selective mortality. We introduce a method that uses the Lande–Arnold framework for examining selection on quantitative traits to empirically reconstruct adaptive landscapes. This method allows the relationship between phenotypic value and fitness components to be described across a broad range of trait values. Our results suggested that despite strong viability selection for large larvae and moderate heritability (h²= 0.29), evolutionary responses of larvae would likely be balanced by reproductive selection favoring mothers that produce more, smaller offspring. Although long‐term evolutionary responses of larval traits may be constrained by size‐number trade‐offs, our results suggest that phenotypic variation in larval size may be an ecologically important source of variability in population dynamics through effects on larval survival and recruitment to benthic populations.     

Size‐dependent reproductive success of wild zebrafish Danio rerio in the laboratory

Size‐dependent reproductive success of wild zebrafish Danio rerio was studied under controlled conditions in the laboratory to further understand the influence of spawner body size on reproductive output and egg and larval traits. Three different spawner size categories attained by size‐selective harvesting of the F₁‐offspring of wild D. rerio were established and their reproductive performance compared during a 5 day period. As to be expected, large females spawned more frequently and had significantly greater clutch sizes than small females. Contrary to expectations, small females produced larger eggs when measured as egg diameter with similar amounts of yolk compared to eggs spawned by large spawners. Eggs from small fish, however, suffered from higher egg mortality than the eggs of large individuals. Embryos from small‐sized spawners also hatched later than offspring from eggs laid by large females. Larval standard length (L_S)‐at‐hatch did not differ between the size categories, but the offspring of the large fish had significantly larger area‐at‐hatch and greater yolk‐sac volume indicating better condition. Offspring growth rates were generally similar between offspring from all size categories, but they were significantly higher for offspring spawned by small females in terms of L_S between days 60 and 90 post‐fertilization. Despite temporarily higher growth rates among the small fish offspring, the smaller energy reserves at hatching translated into lower condition later in ontogeny. It appeared that the influence of spawner body size on egg and larval traits was relatively pronounced early in development and seemed to remain in terms of condition, but not in growth, after the onset of exogenous feeding. Further studies are needed to explore the mechanisms behind the differences in offspring quality between large‐ and small‐sized spawners by disentangling size‐dependent maternal and paternal effects on reproductive variables in D. rerio.     

Oviposition preference,larval performance and adaptation of Trichoplusia ni on cabbage and cotton

Most female herbivores ensure to lay eggs where their offspring can develop successfully. The oviposition preferences of females affect strategies in pest management. In this study, the performance of two cohorts of Trichoplusia ni larvae on cabbage and cotton (after they had been transferred from their original host plants) were investigated. The preferences of female moth ovipositing and larval feeding on these two host plants were observed. The results indicated that plants significantly affected oviposition preference of the female adults and development and survival of larvae of T. ni. All females preferred to lay eggs on cabbage than cotton regardless from which host they originated. The detrimental effects of cotton on the development and survival of T. ni larvae originated from cabbage (CaTn) increased with the increase of the larval age when they were transferred. In addition, the host plant change did not significantly affect the development and survival of larvae of T. ni originating from cotton (CoTn). Larvae of CaTn preferred cabbage plants as compared to cotton plants, whereas larvae of CoTn did not show a significant choice. Although the adult females preferred laying eggs on cabbage, they did not show preferences between cotton and cabbage in a Y‐tube olfactometer test. The hypothesis of oviposition preference and performance of larvae was supported by the results of CaTn, whereas they not supported by those from CoTn. Based on these results, the strategy to manage this serious pest was discussed.     

Polyphagy,flightlessness, and reproductive output of females: a case study with bagworms (Lepidoptera: Psychidae)

Abstract 1. We evaluated the relation between plant‐mediated larval traits and the fitness of female bagworms, Thyridopteryx ephemeraeformis Haworth (Lepidoptera: Psychidae) by sampling 29 populations of bagworms on five plant genera (Thuja, Pinus, Picea, Juniperus, and Gleditsia). 2. Compared with those on other genera of plants, female larvae on Thuja attained a larger size at pupation and developed faster. The superior quality of Thuja as a larval food plant resulted in a higher potential fitness of females, as indicated by a low level of pupal mortality and high fecundity. 3. The fecundity of females increased with pupal size on different plant genera, and the effect of host plant genus was negligible compared with pupal size. 4. The mating success of females varied among different populations (0–37% unmated females), but neither host plant, emergence time, nor the size of females had a significant influence on the proportion of mated females. 5. The conversion of adult biomass into reproductive tissue, measured as the ratio between the biomass of eggs divided by the biomass of calling females, increased with the pupal size of females and approached 90% for large females. The high rate of egg conversion in bagworms may be related to the neoteny of short‐lived females that invest little in somatic tissue.     

Isolation of corn stunt spiroplasma in Jamaica, and probable dual infection with maize mosaic virus

Females of Cydia ptychora oviposited on cowpea, Vigna unguiculata ssp. unguiculata in the field between 18.00 and 19.00 h commencing about 30 days after planting with a few eggs laid on the leafbuds and the undersides of leaves. Oviposition increased as the host plant developed the preferred sites, floral sepals and their remains on pods, and peaked at about 58 days after planting regardless of planting date. First instar larvae were found wandering on the plant between 06.45 and 11.15 h but other larval instars were rarely encountered outside the pod except when changing pods or leaving pods to pupate in the soil. Contrary to previously reported observations, larval development occurred in leafbuds and inside flowers both in the field and in laboratory rearing. Development was optimal on pods, and mortality was high in leafbuds.     

Role of evolutionary and ecological factors in the reproductive success and the spatial genetic structure of the temperate gorgonian Paramuricea clavata

Dispersal and mating features strongly influence the evolutionary dynamics and the spatial genetic structure (SGS) of marine populations. For the first time in a marine invertebrate, we examined individual reproductive success, by conducting larval paternity assignments after a natural spawning event, combined with a small‐scale SGS analysis within a population of the gorgonian Paramuricea clavata. Thirty four percent of the larvae were sired by male colonies surrounding the brooding female colonies, revealing that the bulk of the mating was accomplished by males from outside the studied area. Male success increased with male height and decreased with increasing male to female distance. The parentage analyses, with a strong level of self‐recruitment (25%), unveiled the occurrence of a complex family structure at a small spatial scale, consistent with the limited larval dispersal of this species. However, no evidence of small scale SGS was revealed despite this family structure. Furthermore, temporal genetic structure was not observed, which appears to be related to the rather large effective population size. The low level of inbreeding found suggests a pattern of random mating in this species, which disagrees with expectations that limited larval dispersal should lead to biparental inbreeding. Surface brooding and investment in sexual reproduction in P. clavata contribute to multiple paternity (on average 6.4 fathers were assigned per brood), which enhance genetic diversity of the brood. Several factors may have contributed to the lack of biparental inbreeding in our study such as (i) the lack of sperm limitation at a small scale, (ii) multiple paternity, and (iii) the large effective population size. Thus, our results indicate that limited larval dispersal and complex family structure do not necessarily lead to biparental inbreeding and SGS. In the framework of conservation purposes, our results suggested that colony size, proximity among colonies and the population size should be taken into consideration for restoration projects.     

A field study of potential ecological costs of resistance by ‘stem ducking’ in tall goldenrod,Solidago altissima

Culex quinquefasciatus Say (Diptera: Culicidae) is an abundant urban mosquito that is the vector of filariasis. Breeding in septic tanks, where there are very high levels of bacterial food, it is likely to have a different reaction to crowding compared with other mosquitoes. To test for the presence and type of crowding effects, four larval densities of C. quinquefasciatus varying from 0.4 to 3.2 larvae ml^?1 of water were reared in tubes. Mortality was found to greatly increase at densities above 0.8 larvae, whereas larval duration increased even above 0.4 larvae ml^?1. Changing the water in the tubes daily gave a small (but significant) response in reducing mortality and larval duration. However, when larvae kept at a low density shared the same water with larvae at high density, there was no chemical influence on their growth rate and mortality. The effect of crowding was primarily due to physical disturbances between larvae. When larvae were kept at a high density in the same volume of water, but in shallow trays with a large surface area and therefore much less contact between them, mortality was the same as for the lowest density. There was still, however, a significant increase in larval duration from 8.6 days at 0.4 larvae ml^?1 to 12.1 days at 3.2 larvae ml^?1. It is therefore concluded that the larvae respond to physical rather than chemical factors by prolonging larval development and having some increase in mortality.     

Dispersal of a nearshore marine fish connects marine reserves and adjacent fished areas along an open coast

Marine species with pelagic larvae typically exhibit little population structure, suggesting long‐distance dispersal and high gene flow. Directly quantifying dispersal of marine fishes is challenging but important, particularly for the design of marine protected areas (MPAs). Here, we studied kelp rockfish (Sebastes atrovirens) sampled along ~25 km of coastline in a boundary current‐dominated ecosystem and used genetic parentage analysis to identify dispersal events and characterize them, because the distance between sedentary parents and their settled offspring is the lifetime dispersal distance. Large sample sizes and intensive sampling are critical for increasing the likelihood of detecting parent–offspring matches in such systems and we sampled more than 6,000 kelp rockfish and analysed them with a powerful set of 96 microhaplotype markers. We identified eight parent–offspring pairs with high confidence, including two juvenile fish that were born inside MPAs and dispersed to areas outside MPAs, and four fish born in MPAs that dispersed to nearby MPAs. Additionally, we identified 25 full‐sibling pairs, which occurred throughout the sampling area and included all possible combinations of inferred dispersal trajectories. Intriguingly, these included two pairs of young‐of‐the‐year siblings with one member each sampled in consecutive years. These sibling pairs suggest monogamy, either intentional or accidental, which has not been previously demonstrated in rockfishes. This study provides the first direct observation of larval dispersal events in a current‐dominated ecosystem and direct evidence that larvae produced within MPAs are exported both to neighbouring MPAs and to proximate areas where harvest is allowed.     

Wise flies: a pre‐dispersal seed predator prefers hermaphrodites over females in the gynodioecious Polemonium foliosissimum

1. Oviposition choices can profoundly affect offspring performance. Oviposition decisions of the dipteran pre‐dispersal seed predator, Hylemya sp. (Diptera: Anthomyiidae), when choosing among sex morphs of their host‐plant—Polemonium foliosissimum Hook—were evaluated. Polemonium foliosissimum is gynodioecious, with female and hermaphrodite sex morphs that differ in flower size. 2. It was asked: Do female flies preferentially oviposit on hermaphrodite plants and, if so, are oviposition choices correlated with flower size? Is larval survivorship higher on hermaphrodite plants and, if so, is larval success correlated with flower size? Can the differences in oviposition and/or larval success be explained by slight differences in flowering phenology between the sexes? 3. Hermaphrodite flowers received 45% more Hylemya eggs than females. Although hermaphrodites had larger petals and sepals than females, egg loads were not correlated with petal or sepal size. Larval survival was 30% greater on hermaphrodites than females and higher on plants with larger sepals. However, the difference in sepal area between genders did not fully explain larval survival differences. Egg numbers declined over weeks, but differences in egg loads between the sex morphs were not attributable to a slight phenological delay of females. Larval survival declined over the season; however, larval survival differences between sex morphs were consistent. 4. Hylemya preferentially oviposited on hermaphrodites where their larvae had a significantly greater survival rate compared with females. The present results add to the knowledge that intra‐specific choices have consequences for phytophagous insects and that the relationship between antagonists and their gynodioecious host plants is complex.     

Biotypes of the seed beetle Callosobruchus maculatus have differing effects on the germination and growth of their legume hosts

• 1 Populations of the seed beetle Callosobruchus maculatus (F.) exhibit considerable differences in body size and larval behaviour. We examined whether such variation modifies the relationship between beetle infestation and host plant performance.
• 2 Larvae from African and Asian biotypes were reared in seeds of four hosts that represented an almost four‐fold variation in seed mass. We estimated mass lost to larval consumption, and compared germination rates and seedling growth between infested and control seeds.
• 3 In seeds bearing a single larva, the larger‐bodied, contest‐competing larvae of the Asian biotype caused a 38–47% greater reduction in seed mass compared with the smaller‐bodied, scramble‐competing larvae of the African biotype. The amount of seed mass lost per larva remained similar in seeds with one or two scramble‐competing larvae but decreased significantly in seeds bearing two contest‐competing Asian larvae.
• 4 Differences in larval consumption and behaviour produced striking differences in the frequency of germination. Germination of singly‐infested mung bean (i.e. the smallest host) was 71% for African‐infested seeds versus 11% for Asian‐infested seeds. In cowpea (i.e. the largest host), 76% of Asian‐infested seeds germinated, whereas the germination rate of African‐infested cowpeas (92%) was similar to that of uninfested seeds.
• 5 Effects of beetle origin persisted after germination. Seedlings derived from Asian‐infested seeds had greater cotyledon damage 7 days after germination, and displayed lower height and less biomass 15 days after germination. Cotyledon damage was a good predictor of seedling performance (i.e. better than seed mass consumed) 15 days after germination.
• 6 Previous studies have suggested that population differences in larval size and burrowing behaviour (‘centripetal tendency’) reflect adaptation to different‐sized seeds. The present study demonstrates that these differences in turn influence the impact of larval feeding on host viability. Strong biotypic variation makes it difficult to generalize about pest impacts at the level of pest species.