The yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae), is an important industrial insect commercially produced around the world as food and feed. Temperature and nutrition are the two most influential environmental factors determining the rearing conditions in insects, but little is known about how these two factors interact to affect the performance of T. molitor larvae. In this study, we investigated the combined effects of temperature and dietary protein:carbohydrate (P:C) ratio on key performance traits in T. moltior larvae. Throughout their larval stage, the insects were reared on one of 36 treatment combinations of six temperatures (19, 22, 25, 28, 31, 34 °C) and six protein:carbohydrate ratios (P:C = 1:5, 1:2, 1:1, 2:1, 5:1, 1:0) and their survivorship, development, growth rate, and pupal mass were monitored. Survivorship was high at low temperatures (< 25°C) and high P:C ratios (>1:1), but decreased with increasing temperature and decreasing P:C ratio. Increase in rearing temperature accelerated larval development but resulted in a reduced pupal mass. Thermal optimum for pupal mass (19.3°C) was thus lower than that for development time (28.1°C). The growth rate was maximized at 27.9°C and P:C 1.65:1 and decreased as both the temperature and the P:C ratio deviated from their optimum. All four key performance traits (survivorship, development time, pupal mass, growth rate) were optimized at temperatures between 25.7 and 27.4°C and P:C ratios between 1.17:1 and 2.94:1. Our data provide insights into how the production and nutritional value of T. molitor larvae can be improved through adjusting their rearing conditions.

영양은 모든 생명활동의 근본이며, 생물의 진화적 적응도를 결정하는 가장 중요한 요인이다. 곤충영양학은 곤충생리학의 전통적인 연구영 역이며, 최근 산업곤충의 대량사육 필요성이 증가함에 따라 그 중요성이 부각되고 있다. 이러한 중요성에도 불구하고, 곤충의 영양현상을 정확히 이해하기란 어려운데, 이는 영양의 다변량적 특성, 영양소 간의 교호작용 등으로 설명되는 영양적 복잡성에 기인한다. 영양기하학(Nutritional Geometry)은 이러한 난점을 극복하기 위해 고안된 통합적이고 다차원적인 분석모형으로서, 최근 곤충영양학이 급격하게 발전할 수 있는 이론적 및 실험적 기반을 제공하였다. 본 종설은 영양기하학의 기본개념을 소개하고, 이러한 방법론이 어떻게 최근 곤충영양학의 급속한 학문적 진보를 가능케 하였는지, 그리고 영양이 어떻게 생리학, 생태학, 진화생물학을 통합하는 구심점이 될 수 있었는지를, 최신 연구사례를 중심으로 살펴볼 것이다. 또한 본 종설은 향후 영양기하학을 적용함으로써 발전할 가능성이 높은 연구분야를 고찰할 것이다.

Temperatures experienced during larval development can exert profound effects on life-history traits expressed later during the adult stage in insects. In this study, we explored how larval rearing temperature (18, 23, and 28℃) would affect adult lifespan and reproductive performance in Drosophila melanogaster Meigen (Diptera: Drosophilidae). Larval developmental period was shortened with increasing rearing temperature. Larvae reared at colder temperatures reached the adult stage at a larger size than those reared at higher temperatures, thus conforming to the temperature-size rule. More importantly, we found strong evidence for significant effects of larval rearing temperature on both adult lifespan and early-life egg production rate. Lifespan increased progressively as the larval rearing temperature decreased from 28 to 18℃. In contrast, egg production rate was lower for flies raised at 18℃ compared to those at 23 and 28℃. These results highlight the importance of thermal environments experienced during the development in shaping life-history plasticity in insects.

Different laboratory strains of Drosophila melanogaster are reported to differ considerably in their physiology, behavior, and life-histories, due to their adaptations to different laboratory conditions. Recent advances in insect aging research have highlighted the importance of protein:carbohydrate (P:C) balance as a key dietary determinant of lifespan and other components of fitness, but it remains unexplored whether P:C balance affects the fitness-related traits of D. melanogaster in a strain-specific manner. The purpose of this study was to compare the life-history consequences of six different laboratory strains of D. melanogaster (three Canton-S substrains, w1118, yw, and Oregon-R) allocated to four synthetic diets differing in P:C ratio (1:16, 1:4, 1:1, or 4:1). Five components of fitness (lifespan, fecundity, larval viability, development time, and body mass) were recorded from flies maintained at 25oC under L:D 12:12 photoperiod. All strains exhibited qualitatively similar responses to dietary P:C balance, with the increase in P:C ratio being associated with shortened lifespan and improved egg production. In all strains, fly larvae confined to P:C 1:16 suffered high mortality, retarded growth, and reduced body size. As indicated by significant diet×strain interactions for all measured fitness components, the magnitude of such diet effect varied among different laboratory strains in D. melanogaster. Possible explanations for such strain differences are discussed.

Diet and temperature are the two most critical environmental factors affecting life-history traits in insects, but the combined effects of these factors have been rarely investigated. In this study, various life-history traits were recorded from adult and larval Drosophila melanogaster fed on one of eight synthetic diets differing in protein:carbohydrate ratio (P:C=1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, or 8:1) under one of six ambient temperatures (13, 18, 23, 28, 31, or 33oC). The patterns of adult and larval life-history traits expressed across 48 diet-by-temperature combinations were visualized using thin-plate spline technique and the presence of any significant linear, quadratic, and correlational effects of diet and temperature on trait expressions was analyzed using a second-order polynomial multiple regression. Life-history traits exhibited qualitatively different responses to variations in both diet and temperature, with the maximal expression of each trait being achieved at a completely divergent region of the diet-temperature fitness landscape. In adult females, for example, lifespan was maximized at P:C 1:16 under 13oC, but fecundity was maximized at P:C 4:1 under 28oC. These results provide empirical support for the emerging notion that environmental factors, such as diet and temperature, can mediate life-history trade-offs in insects.

Diets influence lifespan and reproduction in insects, but little is known how temperature modulates the impacts of diet on these two key fitness components. Here we examined the interactive effects of temperature and nutrient balance on lifespan and egg production rate in Drosophila melanogaster. Newly emerged adult D. melanogaster were allowed to feed ad libitum on one of eight chemically defined diets differing in P:C ratio (1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, or 8:1) under one of six ambient temperatures (13, 18, 23, 28, 31, or 33℃). For both males and females, lifespan was longest for D. melanogaster fed on P:C 1:16 diet at 13℃ and shortened as both temperature and P:C ratio increased. As indicated by a significant temperature-by-diet interaction for lifespan, the diet effects on lifespan were more pronounced at lower temperatures than at higher temperatures. Egg production rate was maximized on P:C 4:1 diet at 28℃.

Protein and carbohydrate are two major macronutrients that exert profound influences over fitness in many insects, including Drosophila melanogaster. Until recently, most studies examining the impacts of these macronutrients on various life-history traits in this species have used semi-synthetic diets that are not nutritionally well-defined. Here we used chemically defined diets to examine the patterns of larval and adult traits expressed across 34 diets systematically varying in the ratio and concentration of protein and carbohydrate. The shapes of the nutritional landscapes plotted for all larval and adult traits differed significantly from one another. Diverging nutritional optima identified for these landscapes suggest that D. melanogaster cannot maximize the expression of all life-history traits simultaneously, thus leading them to face a nutrient-dependent life-history trade-off.

Temperature can modulate how insects respond to environmental stressors, such as starvation. In this study, we examine whether and how the effects of temperature on starvation resistance depend on nutritional condition and developmental stages in Drosophila melanogaster. Starvation resistance decreased as the temperature exposed during starvation rose from 18 to 28 ̊C, which was mainly caused by warming-induced increase in energy expenditure. When exposed to warm temperatures during feeding, D. melanogaster accumulated more energy reserves and thus become more starvation resistant. The temperature experienced during the larval stage also had a significant effect on starvation resistance at adult stages, with those larvae raised at cold temperatures developing into adult phenotypes with reduced resistance to starvation. This study suggests that the effects of temperature on starvation resistance are highly complex and context dependent in D. melanogaster.

Environmental temperature has strong impacts on the rate and efficiency of nutrient use in insects, but little is knownabout how changes in temperature influence their nutrient preference. Here we examined the effect of temperature onthe nutrient preferences of mealworm beetles (Tenebrio molitor L.) by offering them a choice between two nutritionallycomplementary diets (P:C 1:5 vs. 5:1) at four different temperatures (20, 25, 30, or 35 ̊C). Beetles selected protein andcarbohydrate in a 1:1 ratio at 25 and 30 ̊C, but exhibited a significant preference for carbohydrate at 20 and 35 ̊C. Theseresults indicate that nutrient preference can shift plastically to match the altered nutrient requirement of beetles underchanging thermal conditions. The present findings have implications for the impacts of climate warming on diet selectionin insects.

Temperature can affect the ability of insects to tolerate prolonged period of food deprivation through altering the amountof energy storage, the speed of energy expenditure, or the threshold energy storage for survival. In this study, we examinedthe mechanistic basis of the temperature-dependence of starvation resistance in Drosophila melanogaster. Starvation resistancedecreased as the temperature experienced during starvation rose from 18 to 28 ̊C. This warming-mediated decrease instarvation resistance was due to accelerated energy expenditure. However, the threshold energy storage for survival wasnot affected by starvation temperature. Exposure to warm temperatures during feeding led D. melanogaster to accumulatemore energy reserves and thus to become more starvation resistant. This study highlights the important role played bytemperature in shaping the phenotypic responses of insects to starvation.

Recent research has suggested that the dietary protein:carbohydrate (P:C) balance is a critical determinant of fitness in insects. In this study, we examined the effects of dietary P:C balance on life-time reproductive success in the mealworm beetle, Tenebrio molitor. Both males and females lived the longest when fed on P:C 1:1 diet. Throughout their adult lives, females fed on P:C 1:1 diet laid significantly more eggs than those on nutritionally imbalanced diets (P:C 1:5 or 5:1). When given a choice, beetles regulated their intake of protein and carbohydrate to a ratio close to 1:1. Taken together, our results indicate the balanced intake of protein and carbohydrate maximizes life-time reproductive success in this species.

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.