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.

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.

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.

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.

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.