SEASONALLY VARYING DIET QUALITY AND THE QUANTITATIVE GENETICS OF DEVELOPMENT TIME AND BODY SIZE IN BIRCH FEEDING INSECTS

Abstract Genetic variance‐covariance structures (G), describing genetic constraints on microevolutionary changes of populations, have a central role in the current theories of life‐history evolution. However, the evolution of Gs in natural environments has been poorly documented. Resource quality and quantity for many animals and plants vary seasonally, which may shape genetic architectures of their life histories. In the mountain birch‐insect herbivore community, leaf quality of birch for insect herbivores declines profoundly during both leaf growth and senescence, but remains stable during midsummer. Using six sawfly species specialized on the mountain birch foliage, we tested the ways in which the seasonal variation in foliage quality of birch is related to the genetic architectures of larval development time and body size. In the species consuming mature birch leaves of stable quality, that is, without diet‐imposed time constraints for development time, long development led to high body mass. This was revealed by the strongly positive phenotypic and genetic correlations between the traits. In the species consuming growing or senescing leaves, on the other hand, the rapidly deteriorating leaf quality prevented the larvae from gaining high body mass after long development. In these species, the phenotypic and genetic correlations between development time and final mass were negative or zero. In the early‐summer species with strong selection for rapid development, genetic variation in development time was low. These results show that the intuitively obvious positive genetic relationship between development time and final body mass is a probable outcome only when the constraints for long development are relaxed. Our study provides the first example of a modification in guild‐wide patterns in the genetic architectures brought about by seasonal variation in resource quality.     

ADAPTIVE PHENOTYPIC PLASTICITY IN GROWTH,DEVELOPMENT, AND BODY SIZE IN THE YELLOW DUNG FLY

Life-history theory predicts that age and size at maturity of organisms should be influenced by time and food constraints on development. This study investigated phenotypic plasticity in growth, development, body size, and diapause in the yellow dung fly, Scathophaga stercoraria. Full-sib families were allowed to develop under predator-free field conditions. The time before the onset of winter was varied and each brood was split into three environments differing in the amount of dung a set number of larvae had as a resource. When resources were abundant and competition was minimal, individuals of both sexes grew to larger body sizes, took longer time to mature, and were able to increase their growth rates to attain large body sizes despite shorter effective development periods later in the season. In contrast, limited larval resources and strong competition constrained individuals to mature earlier at a smaller adult size, and growth rates could not be increased but were at least maintained. This outcome is predicted by only two life-history optimality models, which treat mortality due to long development periods and mortality due to fast growth as independent. Elevated preadult mortality indicated physiological costs of fast growth independent of predation. When larval resources were limited, mortality increased with heritable variation in development time for males, and toward the end of the season mortality increased as larval resources became more abundant because this induced longer development periods. Sexual and fecundity selection favoring large body size in this species is thus opposed by larval viability selection favoring slower growth in general and shorter development periods when time and resources are limited; this overall combination of selective pressures is presumably shaping the reaction norms obtained here. Flexible growth rates are facilitated by low genetic correlations between development time and body size, a possible consequence of selection for plasticity. Heritable variation was evident in all traits investigated, as well as in phenotypic plasticity of these traits (genotype X interactions). This is possibly maintained by unpredictable spatiotemporal variation in dung abundance, competition, and hence selection.     

How to become large quickly: quantitative genetics of growth and foraging in a flush feeding lepidopteran larva

Rapid larval growth in insects may be selected for by rapid ephemeral phenological changes in food resources modifying the structure of phenotypic and genetic (co)variation in and among individual traits. We studied the relative effects of three processes which can modify expression of additive genetic and nongenetic variation in traits. First, natural selection tends to erode genetic variation in fitness-related traits. Second, there may be high variance even in traits closely coupled with fitness, if these traits are themselves products of variable lower level traits. Third, traits may be canalized by developmental processes which reduce phenotypic variation. Moreover, we investigated the phenotypic and genetic role played by the underlying traits in attaining simultaneously both large size and short development time. We measured phenotypic and genetic (co)variation in several pre- and post-ingestive foraging traits, growth, development rate, development time and size, together forming a hierarchical network of traits, in the larvae of a flush feeding geometrid, Epirrita autumnata. Rapid larval growth rate and high pupal mass are closely related to fitness in E. autumnata. Traits closely associated with larval growth displayed low levels of additive genetic variation, indicating that genetic variability may have been exhausted by selection for rapid growth. The body size of E. autumnata, in spite of its close correlation with fitness, exhibited a significant additive genetic variation, possiblye because caterpillar size is the outcome of many underlying heritable traits. The low level traits in the hierarchical net, number (indicating larval movements) and size of feeding bouts in leaves, relative consumption rate and efficiency of conversion of ingested food, displayed high levels of residual variation. High residual variation in consumption and physiological ability to handle leaf material resulted from their flexibility which reduced variation in growth rate, i.e. growth rate was canalized. We did not detect a trade-off between development time and final size. On the contrary, large pupal masses were attained by short larval periods, and this relationship was strongly genetically determined, suggesting that both developmental time and final size are expressions of the same developmental process (vigorous growth) and the same genes (or linkage disequilibrium).     

Critical weight in the development of insect body size

Body size is one of the most important life history characters of organisms, yet little is known of the physiological mechanisms that regulate either body size or variation in body size. Here, we examined one of these mechanisms, the critical weight, which is defined as the minimal mass at which further growth is not necessary for a normal time course to pupation. The critical weight occurred at 55% of peak larval mass in laboratory-reared larvae of the tobacco hornworm Manduca sexta. We examined the effects of genetic and environmental variation in the critical weight on body size. As in many other insects, Manduca larvae reared on poor diets were smaller and those reared at lower temperatures were larger than control animals. We demonstrated that the critical weight was lower on low quality diets but did not change with temperature. There was significant genetic variation for body size, for plasticity of body size, and for critical weight, but not for plasticity of critical weight. Variation in the critical weight accounted for 73% of between-family variance in peak larval size, whereas plasticity of critical weight was not significantly correlated with plasticity of body size. Our results suggest that although critical weight is an important factor in determining body size and enabling the evolution of body size, it may, at the same time, act as a constraint on the evolution of plasticity of body size. Thus, the determinants of body size and the determinants of plasticity of body size do not need to be identical.     

Diversity of birch sawfly responses to seasonally atypical diets

Most insect herbivores are specialised on a particular plant taxon. To have a better understanding of host shift functions and consequences for insect herbivores, it is essential to gather more information on the effects of variation in host quality on specialists across species and environments. We examined the effects of seasonally atypical food on mortality, developmental time, and final body mass of six sawfly species (Hymenoptera: Symphyta) feeding on the foliage of mountain birch (Betula pubescens ssp. czerepanovii), whose pooled larval feeding periods form a gradient and cover the growing season. Insect phenology was manipulated so that the larvae of early-season species would feed on atypically mature leaves and mid- or late-season species would feed on atypically young leaves of their major host plant. Mortality increased dramatically for all species when the larval feeding schedule was advanced or delayed. This indicates a high degree of specialisation not only on a particular host but also to its phenological phases. The main cause of mortality on novel food was a rejection of the diet by the young larvae and their subsequent starvation. An interesting observation was that late-season species showed this response on nutritious young foliage. The effects of seasonally atypical diets on larval development and growth were species-specific and milder than the effects on mortality. Interestingly, for those individuals that accepted it, atypical food seemed to be most beneficial for species appearing at both ends of the seasonal gradient, which might be related to a wider exposure to variable food quality in natural conditions compared with other species. The diversity of responses to atypical food among closely related herbivore species with overlapping feeding periods on the same host plant is the most crucial finding of this study.     

Development time and size-related traits in the oriental blowfly, Chrysomya megacephala along a latitudinal gradient from China

Organisms can respond to variation in temperature through the direct effect of temperature on phenotypes (phenotypic plasticity), or through long-term adaptation to temperature (and thus evolution of either mean size or thermal reaction norm). We examined the effects of various temperatures (of 20 and 30 °C) on development time, adult body size (body length and body width) and pre-adult survivorship in six populations of Chrysomya megacephala, collected at different latitudes. We found that temperature changes induced substantial plasticity in terms of development time, body size and pre-adult survivorship, indicating that developmental temperature significantly affects growth and life history traits of C. megacephala. We also detected genetic differences among populations for body size and development time, and these two traits exhibited highly significant variations in the responses of different populations to various temperature conditions, indicating genetic differences among populations in terms of thermal reaction norms. The latitude of origin of the different populations (and hence mean temperature regimes in the environments from where the populations originated) did not appear to fully explain these genetic differences. In short, changes in development time and body size in C. megacephala can be regarded as adaptations to changing thermal regimes.     

QUANTITATIVE GENETIC DIVERGENCE AND STANDING GENETIC (CO)VARIANCE IN THERMAL REACTION NORMS ALONG LATITUDE

Although the potential to adapt to warmer climate is constrained by genetic trade‐offs, our understanding of how selection and mutation shape genetic (co)variances in thermal reaction norms is poor. Using 71 isofemale lines of the fly Sepsis punctum, originating from northern, central, and southern European climates, we tested for divergence in juvenile development rate across latitude at five experimental temperatures. To investigate effects of evolutionary history in different climates on standing genetic variation in reaction norms, we further compared genetic (co)variances between regions. Flies were reared on either high or low food resources to explore the role of energy acquisition in determining genetic trade‐offs between different temperatures. Although the latter had only weak effects on the strength and sign of genetic correlations, genetic architecture differed significantly between climatic regions, implying that evolution of reaction norms proceeds via different trajectories at high latitude versus low latitude in this system. Accordingly, regional genetic architecture was correlated to region‐specific differentiation. Moreover, hot development temperatures were associated with low genetic variance and stronger genetic correlations compared to cooler temperatures. We discuss the evolutionary potential of thermal reaction norms in light of their underlying genetic architectures, evolutionary histories, and the materialization of trade‐offs in natural environments.     

Genotype–environment interaction and the ontogeny of diet-induced phenotypic plasticity in size and shape of Melanoplus femurrubrum (Orthoptera: Acrididae)

The developmental origin of phenotypic plasticity in morphological shape can be attributed to environment-specific changes in growth of overall body size, localized growth of a morphological structure or a combination of both. I monitored morphological development in the first four nymphal instars of grasshoppers (Melanoplus femurrubrum) raised on two different plant diets to determine the ontogenetic origins of diet-induced phenotypic plasticity and to quantify genetic variation for phenotypic plasticity. I measured diet-induced phenotypic plasticity in body size (tibia length), head size (articular width and mandible depth) and head shape (residual articular width and residual mandible depth) for grasshoppers from 37 full-sib families raised on either a hard plant diet (Lolium perenne) or a soft plant diet (Trifolium repens). By the second to third nymphal instar, grasshoppers raised on a hard plant diet had significantly smaller mean tibia length and greater mean residual articular width (distance between mandibles adjusted for body size) compared with full-sibs raised on a soft plant diet. However, there was no significant phenotypic plasticity in mean unadjusted articular width and mandible depth, and in mean residual mandible depth. At the population level, development of diet-induced phenotypic plasticity in grasshopper head shape is mediated by plastic changes in allocation to tissue growth that maintain growth of head size on hard, low-nutrient diets while reducing growth of body size. Within the population, there was substantial variation in the plasticity of growth trajectories since different full-sib families developed phenotypic plasticity of residual articular width through different combinations of head and body size growth. Genetic variation for diet-induced phenotypic plasticity of residual articular width, residual mandible depth and tibia length, as estimated by genotype–environment interaction, exhibited significant fluctuation through ontogeny (repeated measures MANOVA , family × plant × instar, P < 0.01). For example, there was significant genetic variation for phenotypic plasticity of residual articular width in the third nymphal instar, but not earlier or later in ontogeny. The observed patterns of genetic variation are discussed with reference to short-term constraints and the evolution of phenotypic plasticity.     

The relative importance of temperature and diet to larval development and adult size of the winter stonefly, Soyedina carolinensis (Piecoptera: Nemouridae)

SUMMARY. 1. Soyedina carolinensis Claassen, a leaf shredding stonefly, was reared in a series of three laboratory experiments from early instar to adult on different species of deciduous leaves and at various constant and fluctuating temperature regimes.
2. Experiment 1, which involved rearing larvae on fourteen different leaf diets at ambient stream temperatures, showed that diet significantly affected larval growth and adult size but did not affect overall developmental time.
3. Experiment 2, which involved rearing larvae on five different leaf diets at each of three fluctuating temperature regimes (viz ambient White Clay Creek (WCC), ambient WCC+3°C, and ambient WCC+6°C), showed that: (i) adding 6°C to the normal temperature regime of WCC was lethal to 99% of the larvae regardless of diet; and (ii) warming WCC by 3°C did not affect developmental time but did significantly reduce adult size relative to adults reared at WCC temperatures on certain diets.
4. Experiment 3, which involved rearing larvae on five different leaf diets at each of five constant temperatures (viz 5, 10, 15, 20, 25°C), showed that: (i) temperature significantly affected the mortality, growth, and development time of larvae whereas diet only affected larval growth and mortality; (ii) temperatures at or near 10°C yielded maximum larval growth and survival for most diets; (iii) at 5°C, larval mortality was high and growth was low resulting in a few small adults for most diets; (iv) larval mortality was at or near 100% at 15°C regardless of diet; and (v) no larvae survived at 20 and 25°C.     

Influence of nutrition on male development and reproduction in Tribolium castaneum

Tribolium beetles have evolved over several thousand years to colonize and exploit various food products that vary widely in their nutritional quality. Here Tribolium castaneum was used as a model organism to explore the effect of nutritional quality on male development and reproduction. The results showed, when tested across different qualities of nutritional diets, Tribolium males developed faster and their body size was larger on a high-quality diet, and there were significant correlations between male developmental traits. However, Tribolium males fed different nutritional diets did not show significant variation in olfactory attractiveness, mating rate, insemination rate, sperm defense (P1), sperm offense (P2), and reproductive success within a population context (RSPC). Moreover, there was no significant correlation of male reproductive performances except RSPC with developmental traits, and except for P2 and RSPC, no significant correlations between male reproductive performances. Therefore, although male developmental performance was significantly influenced by diet quality, reproductive performance was not. We discussed these findings and their sexual selection implications in light of its habitat.     

Plasticity of fish body shape. The effects of diet, development, family and age in two species of Geophagus (Pisces: Gichlidae)

Fish body shape is affected by the genetic makeup of an individual as well as environmental influences, such as diet, development, growth rate and nutrition. Fishes in the family Cichlidae exhibit tremendous morphological diversity in body shape and morphology related to feeding. Certain aspects of cichlid feeding morphology have been shown to be plastic in response to different diets but plasticity in body shape has not been examined previously. Plasticity affects ecological interactions, the direction and rate of evolution, and has ramifications for characters used in systematic studies. I examined the effect of different diets: chironomid larvae (bloodworms) and brine shrimp nauplii, on body shape in two species of the Neotropical cichlid genus Geophagus which differ in the size at which young begin feeding on external food sources. The fry of G. brasiliensis , a substrate spawner, begin to feed on external food sources earlier than the fry of G. steindachneri , a mouthbrooder. I hypothesized that the difference in size at first feeding could lead to a difference in the amount of plasticity inducible in the two species. The magnitudes of changes were mostly similar, although G. brasiliensis responded to the different diets with slightly greater changes in some of the head measurements. The pattern of changes in the two species were also similar, with fish fed ferine shrimp nauplii developing longer and shallower heads and shallower bodies and tails than fish fed chironomid larvae. I also examined the consequences of considering family and age as additional factors besides diet in G. steindachneri. Considering family or age as additional factors in the analyses did not change the conclusion that different diets induce differences, albeit small ones, in body shape. I argue that morphological plasticity is dependent on behavioural flexibility and that it may enhance evolutionary morphological diversification.     

Body condition, growth rates and diet of Skylark Alauda arvensis nestlings on lowland farmland

Factors affecting the diet, body condition and growth rates of Skylark chicks were assessed to examine their relationship to their agricultural environment during a critical period in the life cycle of this rapidly declining species. Rainfall explained the greatest amount of variation in body condition and growth rates and had a negative effect on both. Body condition indices were a good predictor of the likelihood of future partial brood loss to starvation. Low body condition in grass fields was related to a low diversity in the diet. Chicks fed insect larvae had higher body condition indices than those not fed larvae. Larger broods tended to have higher growth rates than smaller ones, whereas smaller broods tended to have higher body condition indices. Natural brood size reduction through the non-hatching of eggs resulted in higher body condition indices than were found in nests with the same number of chicks where all eggs hatched, this effect being independent of absolute brood size. There was no significant difference between crop types in the distance adult birds flew to forage for food for nestlings and foraging crop destination had no effect on chick development. Differences between crop types in chick diet could be related to the documented effects of pesticides on different prey species. We suggest that recent agricultural changes have affected diet and possibly body condition, but that these effects are unlikely to have been an important factor in recent population declines.     

Phenology of nutritional differences between new and mature leaves and its effect on caterpillar growth

Abstract. 1. We determined the phenology of the shrub Spiraea latifolia Ait. Bork. (Rosaceae), which has indeterminate shoot growth, and the effects of phenological changes in leaf quality on growth rate of the early-spring feeding buckmoth caterpillars, Hemileuca lucina Hy. Edw. (Saturniidae).
2. Leaves, regardless of whether they were newly expanded or several weeks old, were tougher later in the growth season (mid-June) than similarly aged leaves collected earlier; correspondingly, water and nitrogen content for leaves of all ages declined through the larval period. By July, newly expanded leaves had no more nitrogen than mature leaves.
3. Relative growth rate of third instar larvae fed new leaves or a mixture of new and mature leaves in early June was higher than that of those fed mature leaves, and efficiency of conversion of digested food to biomass was higher for larvae fed new leaves than for those fed mature leaves or a mixture.
4. In another experiment, larvae were reared on new leaves through the fourth instar and then fed a diet of new, mature or a combination of new and mature leaves, a regimen that was similar to the phenologies of both plants and caterpillars in the field. There was no difference in time to pupation or pupal weights among these treatments.     

Sources of variation in rapidly inducible responses to leaf damage in the mountain birch-insect herbivore system

Summary Studies on rapidly inducible resistance in trees against insect herbivores show substantial variation in the strength of responses. Here we report the results of a study which examined causes of this variation. We bioassayed the quality of leaves of two developmental phases (young vs. mature) of the mountain birch Betula pubescens ssp. tortuosa by measuring the growth of two instars of Epirrita autumnata larvae. We used only short shoot leaves from trees of a natural stand, uniform in size and age. Damage was caused by larvae and artificial tearing of leaf lamina, varying the scale and time. We separated seasonal changes in plants from instar-dependent effects of the animals by testing experimental larvae in two subsequent growth trials. We found that only larval-made damage induced responses in leaves that made the leaves significantly poorer quality for the test larvae. Artificial damage induced only weak responses, and artificial canopy-wide damage even caused slight improvement of leaf quality. Cumulative leaf damage did not strengthen birch responses. Leaves that were in the expansion phase responded to damage while fully-expanded, mature leaves showed no response. The pattern of responses indicated that there might be physiological constraints: small-scale damage induced resistance against the larvae but largescale damage did not. Prevalent weather conditions might have modified these responses. Larvae of two instars and sexes, of low- and high-density populations responded to leaf damage similarly. However, prior experience of larvae with the host plant may have affected subsequent larval performance. Variation in rapidly inducible responses in birches was caused by plant characters rather than by test animals.     

Resource quality affects weapon and testis size and the ability of these traits to respond to selection in the leaf‐footed cactus bug,Narnia femorata

The size of weapons and testes can be central to male reproductive success. Yet, the expression of these traits is often extremely variable. Studies are needed that take a more complete organism perspective, investigating the sources of variation in both traits simultaneously and using developmental conditions that mimic those in nature. In this study, we investigated the components of variation in weapon and testis sizes using the leaf‐footed cactus bug, Narnia femorata (Hemiptera: Coreidae) on three natural developmental diets. We show that the developmental diet has profound effects on both weapon and testis expression and scaling. Intriguingly, males in the medium‐quality diet express large weapons but have relatively tiny testes, suggesting complex allocation decisions. We also find that heritability, evolvability, and additive genetic variation are highest in the high‐quality diet for testis and body mass. This result suggests that these traits may have an enhanced ability to respond to selection during a small window of time each year when this diet is available. Taken together, these results illustrate that normal, seasonal fluctuations in the nutritional environment may play a large role in the expression of sexually selected traits and the ability of these traits to respond to selection.     

Ontogenetic changes in genetic variances of age-dependent plasticity along a latitudinal gradient

The expression of phenotypic plasticity may differ among life stages of the same organism. Age-dependent plasticity can be important for adaptation to heterogeneous environments, but this has only recently been recognized. Whether age-dependent plasticity is a common outcome of local adaptation and whether populations harbor genetic variation in this respect remains largely unknown. To answer these questions, we estimated levels of additive genetic variation in age-dependent plasticity in six species of damselflies sampled from 18 populations along a latitudinal gradient spanning 3600 km. We reared full sib larvae at three temperatures and estimated genetic variances in the height and slope of thermal reaction norms of body size at three points in time during ontogeny using random regression. Our data show that most populations harbor genetic variation in growth rate (reaction norm height) in all ontogenetic stages, but only some populations and ontogenetic stages were found to harbor genetic variation in thermal plasticity (reaction norm slope). Genetic variances in reaction norm height differed among species, while genetic variances in reaction norm slope differed among populations. The slope of the ontogenetic trend in genetic variances of both reaction norm height and slope increased with latitude. We propose that differences in genetic variances reflect temporal and spatial variation in the strength and direction of natural selection on growth trajectories and age-dependent plasticity. Selection on age-dependent plasticity may depend on the interaction between temperature seasonality and time constraints associated with variation in life history traits such as generation length.     

Reduction of Delia radicum attack in field brassicas using a vertical barrier

According to life‐history theory, longer development time may result in bigger adults. However, reaction norms describing age and size at maturity often follow an L‐shaped form. This relationship is attributable to the simple notion that slowly growing individuals may not lengthen their development excessively after the maturation decision has been made, for example, when development is time limited in seasonal environments. In arthropods, growth occurs within instars, and thus the optimal growth strategy might be mediated by the phenotypic adjustment of instar numbers. We studied the relationship between age and size at maturity of a lichen‐feeding moth, Eilema depressum (Esper) (Lepidoptera: Arctiidae: Lithosiinae), and the variability of instar numbers in relation to achieved adult body mass and time used for maturation. A positive relationship between age and size at maturity was found across developmental pathways and a negative one within the developmental pathways. Directly developing larvae had higher growth rates, attained smaller pupal mass, and passed fewer instars than larvae maturing after overwintering. Host quality did not affect whether larvae matured during the remaining or the next season. High variation in the number of instars together with variable growth rates indicates high plasticity in adaptation to varying environmental conditions. Our results also confirm previous results that instar number variability may be a key characteristic mediating age and size at maturity in insects.     

Developmental responses to variable diet composition in a butterfly: the role of nitrogen,carbohydrates and genotype

Understanding the evolution of herbivore–plant interactions requires detailed information on proximate responses to relevant dietary variability and genetic variance, if any, associated with these responses. We measured the behavioral and developmental responses of Pieris rapae larvae to variation in the nitrogen (N) and carbohydrate (CARB) content of chemically‐defined diets, using differences in the average responses of sibling groups to estimate underlying genetic variance. Larval P. rapae responded to dietary reductions in both N and CARB with increased feeding, but these responses were inadequate to compensate for dietary N deficiencies within the range of N found in host plants. As a result, larvae on reduced N diets exhibited lower relative growth rates and longer development times, whereas larvae on reduced CARB diets maintained normal developmental trajectories. We also report evidence for genetic variation underlying (a) compensatory feeding responses to CARB and N availability, (b) N‐driven variation in growth rate and (c) CARB‐driven variation in larval duration. Our results highlight N availability as a key factor in the growth and development of this herbivorous butterfly, with CARB availability being less constraining and sufficiently addressed by changes to larval consumption rate. Furthermore, our study reveals standing genetic variance associated with larval responses to macronutrient availability, suggesting continued potential for herbivore–plant co‐evolution in this system despite a putative history of strong directional selection.     

Effects of light availability on host plant chemistry and the consequences for behavior and growth of an insect herbivore

We examined how light availability influenced the defensive chemistry of tomato (Lycopersicon esculentum: Solanaceae). Tomato plants were grown either in full sunlight or under shade cloth rated at 73%. Leaves from plants grown in full sunlight were tougher, had higher concentrations of allelochemicals (chlorogenic acid, rutin and tomatine), and had less protein than leaves from plants grown in shade. We determined how these differences in host plant quality due to light availability affected the behavior and growth of a Solanaceae specialist, Manduca sexta. Both in the greenhouse and in the field, caterpillars on shade-grown plants grew heavier in a shorter amount of time than those on plants that had previously been grown in full sunlight. In contrast, the effects of previous light availability to plants on caterpillar behavior appeared to be minor.To further investigate how light availability to plants influenced herbivore growth, we examined the effects of leaf-powder diets made from tomato leaves of different ages (new, intermediate, or mature) grown in full sunlight or shade on caterpillar performance. Caterpillars fed diets made from plants grown in shade consumed less but grew faster than larvae fed diets made from tomato plants grown in full sunlight. Caterpillars fed diets made from new leaves grew larger in less time than caterpillars fed diets made from intermediate aged leaves. Caterpillars did not survive on the mature leaf powder diets. There were plant-light treatment by larval thermal regime interactions. For example, at 26:15 °C , plant-light treatment had no effect on stadium duration, but at 21:10 °C, stadium duration was prolonged with the full sunlight-new leaf diet compared with the shaded-new leaf diet. In a second diet experiment, we examined the interactive effects of protein and some tomato allelochemicals (rutin, chlorogenic acid and tomatine) on the performance of caterpillars. There were food quality by thermal regime interactions. For instance, at 26:15 °C , neither protein nor allelochemical concentration influenced stadium duration, whereas at 21:10 °C, stadium duration was prolonged with the low protein-high allelochemical diet, which simulated full sunlight leaves. In sum, light availability to plants affected defensive chemistry and protein concentration. The difference in food quality was great enough to influence the growth of a specialist insect herbivore, but the effects were temperature-dependent.     

Nutrient balance in medfly, Ceratitis capitata, larval diets affects the ability of the developing insect to incorporate lipid and protein reserves

The Mediterranean fruit fly [Ceratitis capitata Wiedemann (Diptera: Tephritidae)], or medfly, is mass produced in many facilities throughout the world to supply sterile flies for sterile insect technique programs. Production of sterile males requires large amounts of larval and adult diets. Larval diets comprise the largest economic burdens in the mass production of sterile flies, and are one of the main areas where production costs could be reduced without affecting quality and efficacy. The present study investigated the effect of manipulating diet constituents on larval development and performance. Medfly larvae were reared on diets differing in the proportions of brewer's yeast and sucrose. We studied the effect of such diets on the ability of pupating larvae to accumulate protein and lipids, and on other developmental indicators. Except for diets with a very low proportion of brewer's yeast (e.g., 4%), pupation and adult emergence rates were in general high and satisfactory. The ability of pupating larvae to accumulate lipid reserves and proteins was significantly affected by the sucrose and yeast in the diet, and by the proportion of protein to carbohydrates (P/C). In contrast to previous nutritional studies conducted with other insects, low P/C in medfly larval diets (with excess dietary carbohydrates) resulted in pupating medfly larvae having a relatively reduced load of lipids; medfly larvae protein contents in these diets were, as expected, relatively low. Similarly, high P/C ratios in the diet produced larvae with high protein and lipid contents. Differences with other insects may be due to differential post‐ingestion regulation where a high dietary carbohydrate diet reduces the lipogenic activity of the larvae, and induces a shift from lipid to glucose oxidation. Larvae reared on low P/C diets spent more time foraging in the diet than larvae maintained on a high P/C diet, suggesting a compensatory mechanism to complement nutrient intake. The results suggest that the content of brewer's yeast, the most expensive diet component, could be fine‐tuned without apparently affecting fly quality.