Kwang Pum Lee

Understanding the optimal amount and balance of macronutrients required by individual insects is essential for improving the yield and value of insects used as food and feed. Crickets are one of the most widely massproduced edible insects worldwide. Accordingly, there is a growing need to develop dietary formulations that optimize survival, growth, intake, food conversion, and body composition in cricket nymphs. Here, we applied the nutrient landscape approach to examine the combined and interactive effects of dietary protein and carbohydrate on a suite of nutritional traits in eighth‐instar nymphs of the two‐spotted cricket, Gryllus bimaculatus De Geer (Orthoptera: Gryllidae). The crickets were confined to one of 24 chemically defined diets varying in protein‐to‐carbohydrate ratio (P:C = 5:1, 2:1, 1:1, 1:2, 1:5, 1:8) and protein plus carbohydrate concentration (P + C = 21, 42, 63, 84%). Food consumption increased with nutrient dilution, but this compensatory feeding was incomplete. Food utilization efficiency was maximized on nutritionally concentrated diets with a moderately carbohydrate‐biased P:C ratio of 1:1.278. All performance traits were the highest on nutritionally concentrated diets, but each trait was maximized at a different P:C ratio. Cricket nymphs survived best at a highly protein‐biased P:C ratio of 3.861:1. In contrast, both body mass at adult eclosion and relative growth rates (RGR) were maximized at carbohydrate‐skewed P:C ratios of 1:1.473 and 1:1.470, respectively. When offered a food choice, nymphs self‐selected a P:C ratio of 1:1.820, closely aligning with the ratios that maximized body mass and RGR. Body protein content was maximized at a P:C ratio of 1.140:1, whereas body lipid content peaked at 1:5.562. Our results have implications for enhancing the efficiency of cricket farming through diet optimization.

Macronutrients profoundly affect both lifespan and reproduction and also modulate the fundamental trade-off between these two components of fitness in many insects. Beetles represent the largest group of insects, but nutritional interventions in lifespan and reproduction have never been thoroughly explored in this taxon. Here, we used nutritional landscape methodology to determine the effects of protein and carbohydrate intake on lifespan and reproduction in the mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae). The time of death and last reproduction, the number of eggs laid and protein–carbohydrate intake were recorded from beetles maintained on one of 35 chemically defined foods varying in protein-to-carbohydrate ratio (P:C=0:1, 1:5, 1:2, 1:1, 2:1, 5:1 or 1:0) and in protein plus carbohydrate concentration (P+C=25.2%, 33.6%, 42%, 50.4% or 58.8%). Lifespan and reproductive traits increased with higher caloric intake, but their respective trait maxima occurred at different P:C ratios. Female reproductive traits peaked at higher P:C ratios (reproductive lifespan 1:1.06; lifetime egg production 1.31:1; egg production rate 1.75:1) than those maximizing lifespan (male lifespan 1:1.38; female lifespan 1:1.36). This divergence indicates a nutrient-mediated trade-off between lifespan and reproduction in this species. Despite this, the nutritional conflict in T. molitor appeared to be less pronounced than what has been observed in other species commonly used in insect ageing research. When given a food choice, T. molitor beetles selected a P:C ratio close to 1:1, which simultaneously supported extended lifespan and high reproductive output.

Parental environments have profound consequences for offspring fitness through transgenerational transmission of resources and epigenetic factors. Locomotor activity is a functional trait of considerable ecological importance, as it determines the ability of animals to find food and mates and to disperse to more favourable environments. Although there have been studies demonstrating that animals can plastically increase their locomotor capacity in response to nutritionally stressful environments, it remains largely unexplored whether and how parental diet can adjust offspring locomotor capacity and its related traits. In this study, we tested the hypothesis that the parental intake of a nutritionally suboptimal diet would induce hyperactivity in the offspring and that this transgenerational effect could lead to improved offspring performance in an insect herbivore, the bean bug (Riptortus pedestris Fabricius) (Hemiptera: Alydidae). We compared the locomotor activity, metabolic phenotype and performance traits of two groups of R. pedestris nymphs born to parents raised on soybeans [Glycine max (L.) Merr, Fabaceae; standard diet] or peanuts (Arachis hypogaea L., Fabaceae; high‐fat diet). Despite being smaller at birth, the offspring of peanut‐fed parents moved faster and more frequently than those of soybean‐fed parents during their early development. The newly hatched offspring born to peanut‐fed parents had higher relative energy reserves in somatic tissues than those born to soybean‐fed parents, indicating that differential parental provisioning could underpin this parental effect on offspring locomotor activity. Possibly through increased foraging activity, the hyperactive offspring of peanut‐fed parents grew faster into heavier adults than the offspring of soybean‐fed parents, implying that parentally induced increase in offspring locomotor activity is adaptive. This study provides experimental evidence for diet‐mediated transgenerational plasticity of locomotor activity in invertebrates and sheds novel insights into the role of parental diet history in shaping offspring phenotype.

The yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae), is one of the few edible insects commercially produced around the globe as alternative protein sources for food and feed. Temperature and nutrition are the two most influential environmental determinants of growth and development in insects, but little is known about their combined effects in T. molitor. Here we examined how temperature and dietary protein:carbohydrate (P:C) balance act in concert to influence key performance traits in T. moltior larvae reared on one of the 36 treatment combinations of six temperatures (19, 22, 25, 28, 31, and 34 °C) and six protein:carbohydrate ratios (P:C = 1:5, 1:2, 1:1, 2:1, 5:1, and 1:0). Apart from females accumulating higher lipid content than males, there were no sex differences in all measured traits. Survivorship was high at low temperatures (1:1), but decreased with increasing temperature and decreasing P:C ratio. An increase in temperature accelerated development but resulted in reduced pupal mass. Thermal optimum for pupal mass (19.3 °C) was thus much lower than that for development time (28.1 °C). Growth rate peaked at 27.9 °C and P:C 1.65:1 and decreased as both temperature and P:C ratio deviated from their optimum. All four key performance traits (survivorship, development time, pupal mass, and growth rate) were expressed at high levels and, hence, optimized at temperatures between 25.7 °C and 27.4 °C and P:C ratios between 1.17:1 and 2.94:1. Food consumption rate was the highest at a high P:C ratio of 8.4:1, whereas post-ingestive food utilization was the most efficient at a moderate P:C ratio of 1:1.27. The rate and efficiency of food processing were optimized at temperatures between 24.5 °C and 29.9 °C and P:C ratios between 1:1.01 and 3.98:1. Our results have implications for improving the production and nutritional value of T. molitor larvae.

Animals must acquire an ideal amount and balance of macronutrients to optimize their performance, health and fitness. The nutritional landscape provides an integrative framework for analysing how animal phenotypes are associated with multiple nutritional components. Here, we applied this powerful approach to examine how the intake of protein and carbohydrate affects nutrient acquisition and performance in the yellow mealworm (Tenebrio molitor) reared on one of 42 synthetic foods varying in protein and carbohydrate content. Tenebrio molitor larvae increased their food consumption rate in response to nutrient dilution, but this increase was not sufficient to fully compensate for the dilution. Diluting the food nutrient content with cellulose reduced the efficiency of post-ingestive nutrient utilization, further restricting macronutrient acquisition. Tenebrio molitor larvae utilized macronutrients most efficiently at a protein to carbohydrate (P:C) ratio of 1.77:1, but became less efficient at imbalanced P:C ratios. Survivorship was high at high protein intake and fell with decreasing protein intake. Pupal mass and growth rate exhibited a bell-shaped landscape, with the nutritional optima being located around protein-biased P:C ratios of 1.99:1 to 2.03:1 and 1.66:1 to 2.86:1, respectively. The nutritional optimum for development time was also identified at high P:C ratios (1.66:1 to 5.86:1). Unlike these performance traits, lipid content was maximized at carbohydrate-biased P:C ratios of 1:3.88 to 1:3.06. When given a food choice, T. molitor larvae self-composed a slightly carbohydrate-biased P:C ratio of 1:1.24, which lies between the P:C ratios that maximize performance and lipid content. Our findings indicate the occurrence of a nutrient-mediated trade-off between performance and energy storage in this insect.

The black soldier fly (BSF),Hermetia illucens (Diptera: Stratiomyidae), has become one of the most economically important insects that can be a sustainable replacement for traditional feed for swine, poultry, and aquaculture. Despite its emerging importance, studies examining the nutritional requirement of BSF have been scarce. Here we used nutritional geometry approach to determine the separate and combined effects of dietary protein and carbohydrate content on multiple life-history traits and body composition linked to fitness in BSF. BSF larvae were reared on one of 32 chemically defined diets that varied in protein-to-carbohydrate ratio (P:C=1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, or 8:1) and in protein plus carbohydrate concentration (P+C=60, 120, 180, or 240 g/l). Females developed more slowly into larger adults than males, but two sexes responded to dietary variation in protein and carbohydrate in a similar manner. The topography of the nutritional performance landscapes mapped for all measured traits differed significantly from one another, with the optimal P:C ratio being 1:1.71 for preadult survivorship, 1:1.56 – 1:1.11 for development time, 1:3.36 – 1:3.16 for body weight at adult emergence, and 1:1.83 – 1:1.40 for growth rate. Significant divergence in nutritional optima among these components of fitness indicates that the occurrence of fundamental life-history trade-off can be mediated by macronutrient intake. The index representing the preadult performance of BSF had a nonlinear relationship with dietary protein, with the peak centred at the intermediate P:C ratios of 1:1.43 – 1:1.37. The optimal P:C ratio was 1:2.12 – 1:1.70 for lean body weight and 1:14.14 – 1:10.82 for lipid content. Our results highlight the importance of the balanced composition of dietary protein and carbohydrate for optimising BSF performance and have implications for enhancing the mass production of this beneficial species.

The larvae of Zophobas atratus F. (Coleoptera: Tenebrionidae) are a promising source of dietary protein for animal feed. However, there has been no detailed investigation on macronutrient selection and requirement in Z. atratus larvae. Here, we used the geometric framework to explore the behavioural and physiological regulation of protein and carbohydrate in Z. atratus larvae. When provided with pairs of nutritionally imbalanced but complementary foods (choice experiment), Z. atratus larvae self‐composed a diet with a protein‐to‐carbohydrate (P:C) ratio of 1.47:1 or 1.19:1 throughout the experimental period. Across different choice combinations, the intake of carbohydrate was more tightly regulated than that of protein. When confined to one of six foods imbalanced with respect to P:C ratio (no‐choice experiment), Z. atratus larvae regulated their protein–carbohydrate intake to form linear intake arrays across nutrient space in a manner similar to those previously described for other nutritional generalists. The negative slope of the linear intake arrays was shallow (−0.67 to −0.54), suggesting that protein was over‐consumed by Z. atratus larvae to a greater extent than carbohydrates. The nutritional landscapes fitted for larval performance traits exhibited that the performance of Z. atratus larvae was maximized at the P:C ratio of 2:1 and fell rapidly as the P:C ratio decreased below 1:1. There was evidence for post‐ingestive regulation for body nutrient growth through adjusting the utilization efficiencies of ingested protein and carbohydrate. Our results represent the most comprehensive analysis of macronutrient regulation in Z. atratus and have implications for designing an optimal diet for this beneficial insect.