Most ectotherms mature at a larger body size in colder conditions. This negative relationship between developmental temperature and final body size is termed the temperature-size rule. In this study, we investigated how dietary protein:carbohydrate (P:C) balance modulates the fundamental relationship between temperature and body size in the final-instar caterpillars of Spodoptera litura. The magnitude and sign of the thermal reaction norm for body size were altered by the dietary P:C balance of the food eaten by caterpillars. The slope of the reaction norm was flat for caterpillars raised on a nutritionally balanced food (P:C = 1:1) but was negative for those on imbalanced foods (1:5 or 5:1). When allowed to self-compose their preferred diet, caterpillars preferred carbohydrate-rich food at higher temperatures. The negative impact of high temperature on body size was mitigated by such a temperature-driven shift in nutrient preference. This study highlights the importance of macronutrient balance as a key factor modulating the relationship between temperature and body size in insects.

Recent studies have shown that mating can alter starvation resistance in female D. melanogaster, but little is known about the behavioral and physiological mechanisms underlying such mating-mediated changes in starvation resistance. In the present study, we first investigated whether the effect of mating on starvation resistance is sex-specific in D. melanogaster. As indicated by a significant sex × mating status interaction, mating increased starvation resistance in females but not in males. In female D. melanogaster, post-mating increase in starvation resistance was mainly attributed to increases in food intake and in the level of lipid storage relative to lean body weight. We then performed quantitative genetic analysis to estimate the proportion of the total phenotypic variance attributable to genetic differences (i.e., heritability) for starvation resistance in mated male and female D. melanogaster. The narrow-sense heritability (h2) of starvation resistance was 0.235 and 0.155 for males and females, respectively. Mated females were generally more resistant to starvation than males, but the degree of such sexual dimorphism varied substantially among genotypes, as indicated by a significant sex × genotype interaction for starvation resistance. Cross-sex genetic correlation was greater than 0 but less than l for starvation resistance, implying that the genetic architecture of this trait was partially shared between the two sexes. For both sexes, starvation resistance was positively correlated with longevity and lipid storage at genetic level. The present study suggests that sex differences in starvation resistance depend on mating status and have a genetic basis in D. melanogaster.

Macronutrient balance has a strong influence on fitness in insects. Previous studies have revealed that altering the concentrations of yeast and sugar in the semi-synthetic diet has a profound impact on lifespan and fecundity in Drosophila melanogaster, indicating the role of dietary protein:carbohydrate (P:C) balance in determining these two key components of fitness. However, since yeast contains not only proteins but also other macro- and micronutrients, this lifespan-determining role of dietary P:C balance needs to be corroborated using a chemically defined diet. In this study, the effects of dietary P:C balance on lifespan and fecundity were investigated in female D. melanogaster flies on one of eight isocaloric synthetic diets differing in P:C ratio (0:1, 1:16, 1:8, 1:4, 1:2, 1:1, 2:1 or 4:1). Lifespan and dietary P:C ratio were related in a convex manner, with lifespan increasing to a peak at the two intermediate P:C ratios (1:2 and 1:4) and falling at the imbalanced ratios (0:1 and 4:1). Ingesting nutritionally imbalanced diets caused flies to start ageing earlier and senesce faster. Egg production increased progressively as the dietary P:C ratio rose from 0:1 to 4:1. Long-lived flies at the intermediate P:C ratios(1:2 and 1:4) stored a greater amount of lipids than those short-lived ones at the two imbalanced ratios (0:1 and 4:1). These findings provide a strong support to the notion that dietary P:C balance is a critical determinant of lifespan and fecundity in D. melanogaster.

Protein and carbohydrate are the two most important macronutrients that have profound impacts on fitness and demography in most insects. The purpose of this study is to investigate the effects of dietary protein:carbohydrate (P:C) balance and mating status on feeding behavior, longevity and fecundity in male and female mealworm beetles, Tenebrio molitor (Coleoptera: Tenebrionidae). In the first experiment, we measured the amount of protein and carbohydrate consumed by mated and unmated beetles of both sexes. Newly emerged beetles were allowed to mate for 24 h before they were simultaneously provided with two nutritional imbalanced but complementary synthetic diets (P:C =1:5 vs. 5:1) for 24 successive days. Mated females not only consumed significantly more nutrients but also exhibited a greater preference for protein than did mated males and unmated controls. In the second experiment, we determined longevity and fecundity from a total of 120 male and female beetles that were confined to feed on one of three no-choice foods differing in P:C balance (P:C=1:5,1:1 or5:1) throughout their entire lives. Fecundity was recorded as the total number of eggs laid by individual females until death. Both male and female beetles lived significantly longer and laid more eggs over the lifetime on a balanced diet (1:1) than on the two imbalance diets (1:5 and 5:1), suggesting that the Darwinian fitness was maximized when the diet was equally balanced in protein and carbohydrate. Mated male and female beetles had a shorter longevity compared to their unmated counterparts, indicating that there was a significant survival cost to mating in this insect.

Mating elicits a dramatic changes in physiology, behavior, and life-history traits in insects, but little is known about the relationship between mating and the capacity of insects to resist environmental stressors. Starvation is one of the most ubiquitous forms of environmental stress faced by all insects under natural conditions. Previous studies using Drosophila melanogaster flies has shown that mated females lived longer under starvation than did virgin females, but the mechanistic basis for such post-mating increase in starvation resistance remains largely unexplored. The objective of this study was to investigate the behavioral and physiological mechanisms of mating-induced alteration in starvation resistance and its heritable genetic variations in D. melanogaster. In the first experiment (Experiment 1), we compared starvation resistance (measured as starving time before death), body compositions, and food intake between mated and unmated flies of both sexes using a large outbred population. In the second experiment (Experiment 2), starvation resistance and body composition were quantified for mated male and female flies derived from each of 19 highly inbred genetic lines. Results from Experiment 1 showed that mated females were better able to resist starvation than virgin females and males because they ate more and thus laid down more fats in their body. Results from Experiment 2 revealed a significant heritable genetic variation in starvation resistance and its correlated body composition parameters for both sexes. Overall, females had a higher starvation resistance than males, but the magnitude of such intersexual difference varied among genetic lines, as suggested by a significant sex-by-line interaction. Cross-sex genetic correlations were highly significant and positive for starvation resistance, indicating that the genetic factors controlling the starvation resistance in D. melanogaster are shared between the two sexes.

Starvation resistance is an important fitness trait that is controlled by both environmental and heritable factors. The main objective of this study is to explore the genotype-by-nutrient interactions for starvation resistance and its correlating physiological traits in Drosophila melanogaster. In this study, we conducted a split-family quantitative genetic experiment, in which female adults of Drosophila from 19 isofemale genetic lines were allowed to ingest one of two synthetic diets that differed in protein-to-carbohydrate ratio (P:C = 4:1 or 1:16 with the P+C concentration of 120 g L-1) before they were assayed for starvation time and lipid storage. In all genetic lines, Drosophila flies that had fed carbohydrate-rich diet (P:C=1:16) resisted starvation better and stored more lipids than did those that had fed protein-rich diet (4:1). Importantly, the extent to which both starvation resistance and lipid reserves were affected by dietary P:C ratio varied greatly among different genetic lines of Drosophila, as indicated by significant genotypeby-nutrient interactions for these two traits. When the patterns of the bivariate reaction norm for body lipid and starvation resistance were compared across the genotypes, we found strong evidence for genetic variations in the pattern of energy storage and usage associated with maintaining survival under starvation in Drosophila.

The nutritional quality of host plant is critically important for insect herbivores to maximize their fitness, but it is relatively unexplored whether the ingestion of a specific host plant will have the same effects on insects under different thermal conditions. We have used a multi-factorial experimental design to investigate how the nutritional quality of host plant and temperature interact to affect life-history traits in a generalist caterpillar Hyphantria cunea (Lepidoptera: Arctiidae) feeding on five different host plants. Caterpillars raised on Platanus occidentalis, Sophora japonica and Prunus x yedoensis exhibited substantially higher survival, faster growth and heavier mass at pupation than those on Cornus kousa and Betula platyphylla. Caterpillars developed more quickly and attained a smaller final body mass at higher temperatures, but the way that these traits responded to temperature differed by host plant. Caterpillars on P.occidentalis displayed a monotonic decrease in development time with increasing temperature, but the development time of those on P. x yedoensis declined with temperature in a biphasic manner. Furthermore, the rate at which pupal mass increased with decreasing temperature was much greater for caterpillars on P.occidentalis than those on P. x yedoensis.

Nutritional conditions experienced during early growth have important implications for the lifetime fitness of herbivores. We investigated how the early life effects of imbalanced nutrient intake can be overcome in a generalist caterpillar, Spodoptera litura (Lepidoptera: Noctuidae). Over the fifth larval instar, caterpillars were pretreated on one of three diets that varied in protein: carbohydrate balance (p35:c7, p21:c21 or p7:c35). After molting to the sixth instar, they were transferred to one of three no-choice diets (p35:c7 ,p21:c21 or p7:c35) or a food choice where they received two nutritionally complementary diets (p35:c7 versus p7:c35). Approximately 80% of caterpillars that had been protein-deprived (p7:c35) during the fifth instar molted to the seventh instar. The threshold body mass for pupal metamorphosis was 144 mg at the start of the sixth instar. When given a choice, caterpillars pretreated on the low-protein diet (p7:c35) selected significantly more protein than those from other diets (p35:c7,p21:c21). Our results suggest that caterpillars are not only capable of switching their developmental program to reduce the deleterious effects of a nearly deficiency of protein, but also flexible at adjusting nutrient preference store dress specific nutritional imbalances experienced early in life.

Protein and carbohydrate are the two most important macronutrients that have profound consequences for the fitness of insects. Many insects are capable of balancing the intake of multiple nutrients to minimize the fitness costs associated with ingesting diets that are imbalanced with respect to protein and carbohydrate. It has been hypothesized that insects will redress the imbalance of their nutrient state through increasing the appetite for specific nutrients that are ingested in deficit. We tested this possibility using a mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae). Newly emerged beetles were confined to one of two nutritionally imbalanced foods that contained only protein or carbohydrate (P:C ratio = 0:42 and 42:0, expressed as % dry mass) for 16 days, after which they were given an opportunity to choose between two nutritionally imbalanced diets (0:42 versus 42:0). Over the first few days of the food choice, beetles that had previously experienced protein-limitation preferred protein to carbohydrate while the reverse was true for those that had experienced carbohydrate-shortage. Such contrasting patterns of diet preference observed between the two groups of beetles diminished subsequently as the insects recovered from nutrient imbalance. Our results provide strong support for the long-standing idea that attaining the right balance of nutrients is the main motive for foraging in insects.

Food limitation is the most common environmental challenge faced by animals and the capacity of animals to survive prolonged periods of starvation is linked to their diet and nutritional status. The objective of this study is to investigate the effects of nutrition on starvation resistance in Drosophila melanogaster. Experimental flies were given ad libitum access to artificial diets differing in concentrations and ratios of protein and carbohydrate for 5 days before they were assayed for starvation time, body composition and life-history parameters. Starvation resistance in Drosophila was greatly influenced by the dietary protein:carbohydrate (P:C) ratio, but neither by the caloric content of the diet nor by dietary carbohydrate alone. Starvation resistance was strongest at the lowest P:C ratio and declined with rising P:C ratio. While starving, Drosophila underwent a dramatic transition in the utilization of physiological fuels, switching from the early phase characterized by preferential consumption of non-lipid substrates to the next phase in which they began to mobilize lipids as fuels for enduring starvation. Our results highlight the importance of nutrition as a key factor determining starvation responses of Drosophila.

Many insects adjust feeding behavior to meet their optimal requirement for multiple nutrients. In the present study, we investigated the behavioral regulatory responses of male and female adults of an omnivorous beetle, Tenebrio molitor (Coleoptera: Tenebrionidae), using choice and no-choice feeding experimental designs. In the choice experiment, newly eclosed adults of both sexes received one of four food-pairing treatments and so were allowed to self-compose their preferred nutrient intake by selecting between two nutritionally-complementary diets (protein-rich vs. carbohydrate-rich diet; 35:7 vs. 7:35, 35:7 vs. 5.6:28, 28:5.6 vs. 7:35, or 28:5.6 vs. 5.6:28, P%:C% by dry mass). Our data showed that both sexes independently regulated their intake of protein and carbohydrate to a 1:1 ratio, indicating that they are capable of adjusting their feeding behavior to optimize their nutrient preference. In the no-choice experiment, adults were forced to eat one of seven single diets that varied in P:C ratio (0:42, 7:35, 14:28, 21:21, 28:14, 35:7, or 42:0). Results showed that both sexes ingested similar amounts of nutrients when the dietary P:C ratio was moderately balanced (14:28, 21:21 and 28:14), but males ingested significantly more than females on those diets that were extremely imbalanced with respect to their P:C ratio (0:42, 7:35, 35:7 and 42:0). This indicates that there exists a sex-specific difference in nutrient intake when the nutritional balance of diets deviates away from the optimal level under restricted feeding condition.

Temperature and nutrition are the two most important environmental factors influencing growth and survival in immature insects. There is ample evidence of interactions between these two factors but still little is known how changes in thermal environment affect feeding and nutrient utilization insect ectotherms. The aim of this study is to investigate the potential effects of ambient temperature on food selection and post-ingestive nutritional physiology in a generalist-feeding caterpillar of Spodorptera litura. Two separate experiments were performed. The first was a food choice experiment in which caterpillars were maintained through their final larval stadium under one of three constant temperatures(20,25,30°) and given a choice between two nutritionally unbalanced diets that differed in protein(p) and carbohydrate(c) content (p42:c0 vs p7:c35 and p35:c7 vs p7:c35). In the second experiment, caterpillars were kept at the same thermal conditions as the first experiment but received a single diet from three no-choice feeding treatments(p35:c7,p21:c21and p7:c35). When raised at the highest temperature (30C), caterpillars from the choice experiment selected significantly more carbohydrate than those on lower temperatures whereas protein intake did not differ significantly between caterpillars across three test temperatures. Results from the no-choice experiment showed that lipid storage efficiency was reduced when caterpillars were maintained at the highest temperature(30C). In both experiments, growth rate increased progressively with rising temperature. However, there was a significant temperature-by-diet interaction, with growth rates increasing more rapidly on p21:c21 diet than on the other diets(p35:c7 and p7:c35). Our results demonstrate that caterpillars adjust their nutrient preference to meet the increased energetic demand at high ambient temperature.

Foraging is fundamental to animal survival and reproduction, and animals often require more than one nutrient to maximize their evolutionary fitness. Here, we test whether caterpillars of Spodoptera exigua (Hübner) balance the intake of multiple nutrients to meet their nutrient requirement. In the choice test, final-instar larvae were offered a choice of two nutritionally complementary diets [1) p42:c0 vs. p0:c42, 2) p42:c0 vs. p7:c35, 3) p35:c7 vs. p0:c42, 4) p35:c7 vs. p7:c35, 5) p35:c7 vs. p5.6:c28, 6) p28:c5.6 vs. p7:c35 and 7) p28:c5.6 vs. p5.6:c28]. Caterpillars tightly regulated their intake of protein (P) and carbohydrate (C) to defend a specific nutrient composition, which was slightly carbohydrate-biased (P:C=1:1.2). In the no-choice test, larvae were restricted to feed on one of 42 diets that varied both in P:C mixtures (1:0, 5:1, 2:1, 1:1, 1:2 and 1:5) and in total nutrient concentration(P+C=67.2%, 58.8%, 50.4%, 42%, 33.6%, 25.2% and 16.8%). Fitness landscapes fitted for key larval fitness variables (e.g., growth rate) over these range of diets revealed that the larval performance was optimized at the regulated position of nutrient intake in this caterpillar.

The aim of this research was to demonstrate whether generalist-feeding caterpillars of Spodoptera exigua (Hübner) regulate their nutrient intake when faced with nutritionally variable food conditions. Six, chemically-defined diets were prepared that differed in the composition of protein and digestible carbohyrate:42% protein with 0% carbohydrate by dry mass(p42:c0), p35:c7, p28:c5.6, p7:c35, p5.6:c28 and p0:42. A total of 288 newly-ecdysed final instar(5th) caterpillars were collected and assigned randomly into 7 food pairing treatments, in which they were allowed to choose between two diet block:one with high P:C ratio and the other with low ratio [1) p42:c0 vs. p0:c42, 2) p42:c0 vs. p7:c35, 3) p35:c7 vs. p0:c42, 4) p35:c7 vs. p7:c35, 5) p35:c7 vs. p5.6:c28, 6) p28:c5.6 vs. p7:c35 and 7) p28:c5.6 vs. p5.6:c28]. Various aspects of food intake and larval performance variables were measured for each insect, including larval survival, stadium duration, pupal mass and body lipid composition. Results showed that the intake of protein and carbohydrate self-composed by caterpillars in all treatments converged to a point in a bivariate nutrient plot and the ratio of protein to carbohydrate averaged over these converging intake points was close to 1:1. This indicates that S. exigua caterpillars have capacity to balance their nutrient intake by defending their species-specific ‘intake target’ despite the differences in amount and proportion of nutrients available in each food choice treatment.