Influence of dietary nutritional composition on caterpillar salivary enzyme activity

Caterpillars are faced with nutritional challenges when feeding on plants. In addition to harmful secondary metabolites and protein- and water-limitations, tissues may be carbohydrate-rich which may attenuate optimal caterpillar performance. Therefore, caterpillars have multiple strategies to cope with surplus carbohydrates. In this study, we raise the possibility of a pre-ingestive mechanism to metabolically deal with excess dietary sugars. Many Noctuid caterpillars secrete the labial salivary enzyme glucose oxidase (GOX), which oxidizes glucose to hydrogen peroxide and gluconate, a nutritionally unavailable carbohydrate to the insect. Beet armyworm, Spodoptera exigua, larvae were restricted to diets varying in protein to digestible carbohydrate (P:C) ratio (42p:21c; 33p:30c; 21p:42c) and total nutrient concentration (42% and 63%). High mortality and longer developmental time were observed when caterpillars were reared on the C-biased, P-poor diet (21p:42c). As the carbohydrate content of the diet increased, caterpillars egested excess glucose and a diet-dependent difference in assimilated carbohydrates and pupal biomass was not observed, even though caterpillars restricted to the C-biased diet (21p:42c) accumulated greater pupal lipid reserves. Larval labial salivary GOX activity was also diet-dependent and gluconate, the product of GOX activity, was detected in the frass. Unexpectedly, GOX activity was strongly and positively correlated with dietary protein content.     

Temperature‐by‐nutrient interactions affecting growth rate in an insect ectotherm

Temperature and nutrition are two prominent environmental variables influencing juvenile growth rate in ectotherms. These two factors interact in complex ways. Here, we present a comprehensive analysis of the interactive effects of temperature and nutrition on various components of fitness (growth rate, survival), food intake, and level of energy storage in an insect herbivore, caterpillars of Spodoptera exigua Hübner (Lepidoptera: Noctuidae). In a factorial experimental design, final‐instar caterpillars (i.e., fifth instars) were individually reared at one of three constant temperatures (18, 26, and 34 °C), in which they received one of six diets differing in their ratio of protein and digestible carbohydrate [P:C mixture, expressed as the percentage of diet by dry mass: protein 42%:carbohydrate 0% (42:0), 35:7, 28:14, 21:21, 14:28, and 7:35]. Within the range of test temperatures, larval growth rate increased with rising temperature and was strongly affected by P:C mixture, reaching a maximum on moderate P:C diets at each temperature and falling at very high and low P:C mixtures. There was a significant temperature*diet interaction, such that the difference in growth rates between temperatures was greatest on moderate P:C diets and least on the most extreme diets (42:0 and 7:35). Food intake rate patterns followed a similar trend to growth rate. Rapidly growing animals at high ambient temperature suffered high mortality across all dietary P:C mixtures, but to a greater extent on the extremely unbalanced diets. This suggests that there are developmental and physiological costs associated with fast growth at high temperature, as indicated by high rate of pupation failure and reduced lipid storage efficiency. Our study shows how temperature and nutrition interplay to mediate phenotypic variations in growth rates and energy utilization in an insect ectotherm.     

四种昆虫饵料对穴蚁蛉幼虫生长发育及消化利用的影响

选择4种可规模化饲养的昆虫——米蛾Corcyra cephalonica、家蝇Musca domestica、斜纹夜蛾Spodoptera litura、甜菜夜蛾Spodoptera exigu幼虫来饲养穴蚁蛉Myrmeleon sagax(Walker)幼虫(俗称蚁狮),研究这4种饵料对蚁狮生长发育及消化利用的影响。结果显示,用家蝇幼虫饲养的蚁狮,其体重增长、相对生长率、化蛹率、蛹重均显著高于用斜纹夜蛾和甜菜夜蛾幼虫饲养的蚁狮,而幼虫历期则比斜纹夜蛾和甜菜夜蛾幼虫饲养的短;用米蛾幼虫饲养,虽然蚁狮体重增长、化蛹率和蛹重与用家蝇幼虫饲养的差异不显著,但其相对生长率却显著低于用家蝇幼虫饲养的蚁狮,幼虫历期也比用家蝇幼虫饲养的明显延长。同时食物消化利用的结果显示,用4种饵料饲养蚁狮,它们的近似消化率差异不显著,但食物利用率和食物转化率均以家蝇幼虫饲养的蚁狮最高。经分析比较,在4种饵料昆虫中,以用家蝇幼虫每4d喂蚁狮1次的饲养效果最佳。     

The influence of greenhouse chrysanthemum on the interaction between the beet armyworm, Spodoptera exigua, and the baculovirus SeMNPV: parameter quantification for a process-based simulation model

During the building of a process-based simulation model for the epidemiology of the multicapsid nucleopolyhedrovirus of S. exigua (SeMNPV) in populations of Spodoptera exigua (Hübner) in greenhouse chrysanthemum, it was found that the effect of host plants had been under-rated. 'Missing links' included (i) the 'natural' background mortality of larvae of S. exigua in practical cropping conditions; (ii) the developmental rate of larvae of S. exigua on plant substrate in a glasshouse as compared to artificial medium in the laboratory; (iii) the validity of the results of dose-mortality and time-mortality bioassays conducted on artificial medium as compared to natural plant substrate; (iv) the distribution of inoculum released from deceased caterpillars over chrysanthemum leaves; and (v) the leaf visit rate of healthy caterpillars (as it affects horizontal transmission). Experiments were carried out to quantify these processes. Developmental rates of S. exigua larvae on greenhouse chrysanthemum were 36% lower than on an artificial diet. The fraction survival during the first, second, third and fourth instar S. exigua larvae in greenhouse chrysanthemum was 0.60, 0.80, 0.88 and 0.95, respectively. Forty percent of the first instar larvae reached the fifth larval stage. Second instar S. exigua larvae reared on chrysanthemum were significantly more susceptible to SeMNPV than larvae reared on an artificial diet. The food source had no effect on the time to kill S. exigua larvae. Cadavers of second, third and fourth instar S. exigua larvae contaminated on average 1.4, 2.5 and 3.3 chrysanthemum leaves. Second to fourth instar S. exigua larvae visited 2–3 leaves per day and spent 15–55% of the time on the underside of leaves. The above information is of critical importance for a trustworthy simulation of the epidemiology of SeMNPV in chrysanthemum.     

Chemosensory basis of behavioural plasticity in response to deterrent plant chemicals in the larva of the Small Cabbage White butterfly Pieris rapae

Behavioural and electrophysiological responsiveness to three chemically different secondary plant substances was studied in larvae of Pieris rapae L. (Lepidoptera: Pieridae). Three groups of caterpillars were studied that during their larval development were exposed to different rearing diets: an artificial diet or one of two host-plants, cabbage, Brassica oleracea, or nasturtium, Tropaeolum majus. In dual-choice leaf disc assays, caterpillars reared on cabbage were strongly deterred by the phenolic chlorogenic acid, the flavonol glycoside naringin and the alkaloid strychnine. However, behavioural plasticity was found in caterpillars reared on nasturtium or artificial diet in that these did not discriminate against chlorogenic acid. Caterpillars reared on the artificial diet were also significantly less sensitive to naringin and strychnine in the behavioural assay. Electrophysiological studies of the maxillary sensilla styloconica revealed that the deterrent neuron in the medial sensillum, but not in the lateral sensillum, of cabbage-reared caterpillars was more sensitive than the same neuron type of caterpillars reared on nasturtium or artificial diet. We conclude that (1) the diet-induced behavioural habituation to deterrents can at least partly be explained by chemosensory desensitisation of a generalist type of maxillary deterrent neuron; (2) behavioural cross-habituation to the three structurally diverse deterrent compounds can be traced back to cross-sensitivity for these compounds in the same gustatory neuron.     

Host plant selection and development in Spodoptera exigua: do mother and offspring know best?

We examined the ovipositional preference and larval development of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) on two common hosts in southern California, Chenopodium murale L. (Chenopodiaceae) and Apium graveolens L. (Umbelliferae) to determine if female oviposition preference is correlated with offspring performance. Greenhouse oviposition choice tests indicated that S. exigua oviposit more frequently on C. murale than on A. graveolens. However under laboratory conditions, larvae reared on C. murale had longer development times, lower relative growth rate, and lower survivorship than larvae reared on A. graveolens. larval and pupal masses were significantly greater on A. graveolens than on C. murale. Furthermore, pupal masses were significantly greater for individuals reared on A. graveolens than on C. murale. Because pupal masses and adult fecundity are positively correlated for Spodoptera spp., the fitness of S. exigua on A. graveolens is likely to be substantially higher than its fitness on C. murale. Despite better larval performance on A. graveolens, previous results from choice tests with whole plants and leaf discs indicate that the highly mobile S. exigua larvae strongly prefer C. murale over A. graveolens. Hypotheses attempting to explain this lack of correlation between larval and adult host preference versus development and survival in this system are discussed.     

Effect of modified meridic diet on the development and growth of tomato fruitworm Helicoverpa armigera (Lepidoptera: Noctuidae)

The efficacy of one new modified and two old meridic diets on Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) for rearing six successive generations was studied. Duration of larval development for insects fed on the modified diet was considerably shortened as most of them went through only five stadia before pupation, while the per cent pupation and per cent eclosion were relatively higher than on other diets. The lowest pupal mortality (6.33 ± 0.13%) was recorded in the F₁ generation reared on the modified diet, whereas the highest pupal mortality (19.49 ± 0.15%) was observed in insects reared on a natural diet in the F₆ generation. Blending of chickpea Cicer arietinum L. and red kidney bean Phaseolus vulgaris L. flours with tomato paste proved highly favorable for adult reproduction. These results suggest that the vitality of the tomato fruitworm did not decline obviously after rearing on a modified diet for several generations.     

幼虫食物对甜菜夜蛾生长发育、繁殖及飞行的影响

报道了人工饲料、圆白菜和玉米苗三种食物对甜菜夜蛾Spodoptera exigua发育历期、蛹重以及成虫产卵和飞行能力的影响。幼虫取食人工饲料时发育历期最短,蛹最重(138 mg),产卵量最高(643粒);在12 h的吊飞测试中,成虫飞行距离最远(25.5 km),飞行时间最长(6.2 h),飞行超过10 km的个体占67.9%,超过5 h的占60.7%。幼虫取食玉米苗时发育历期最长,蛹最轻(52 mg),产卵量最低(416粒),成虫仅能飞行3.3 km,1.7 h,飞行超过10 km或5 h的个体均仅占4.2%,各项指标均显著低于人工饲料组。幼虫取食圆白菜时各项指标与人工饲料组基本相似(幼虫历期和蛹重除外),而显著优于玉米苗组(幼虫历期除外)。这些结果表明,幼虫食物对甜菜夜蛾的生长发育、产卵及飞行能力均有显著的影响,因而是影响其个体发育、种群增长及种群动态的重要因素之一。同时,由于取食本人工饲料的各项指标均优于其它两种食料植物,因而可作为饲养甜菜夜蛾的实用饲料。     

甜菜夜蛾的饲养方法介绍

介绍一种甜菜夜蛾的室内饲养方法 ,采用本方法累代饲养甜菜夜蛾 8代 ,平均蛹重达 1 1 2 .9mg ,平均化蛹率 97% ,平均羽化率为 91 .3% ,室内饲养结果表明 ,该饲养方法可用于室内大量饲养甜菜夜蛾     

Compensatory responses of the fall armyworm (Spodoptera frugiperda) when fed water- and cellulose-diluted diets

Abstract Caterpillars of the noctuid moth, Spodoptera frugiperda (J. E. Smith), reared on artificial diets diluted with cellulose and water, increased fresh weight (fw) consumption 2.2–2.5-fold over those on the undiluted diet. At moderate levels of water- or cellulose-dilution, the increased consumption, combined with increased digestion and absorption of nutrients (ADNU), sufficiently compensated for the reduced nutrient intake to achieve pupal biomass equivalent to that of pupae from the undiluted diet. At higher levels of water- and cellulose-dilution, fw consumption and ADNU increased further but pupal dry weight declined on the water-diluted diets. At each level of dilution fw consumption and ADNU increased similarly on the water- and cellulose-diluted diets, but biomass gain was reduced on the water- compared with the cellulose-diluted diets. This was due in part to lowered food conversion efficiency on the water-diluted diets, possibly caused by increased costs of metabolizing the wetter diets. Our data support the hypothesis that consumption rates are regulated by a nutrient feedback mechanism. Our data also suggest that digestive enzyme activity is correlated with consumption. Furthermore, the cost of increased consumption rates on diets of reduced energetic value may constitute a substantially greater energy expenditure than previously believed. However, this cost was insufficient to reduce relative growth rates but was apparently manifested in lowered lipid accumulation.     

New larval agar-based diet for laboratory rearing of Mediterranean fruit fly <Emphasis Type="Italic">Ceratitis capitata</Emphasis> (Diptera,Tephritidae)

Five larval diets for laboratory rearing of Ceratitis capitata were tested. These diets were based on wheat bran, microcellulose, potato starch and agar. To evaluate the quality of diet, pupal rearing efficacy and pupal weight were checked. The best results were obtained with an agar based diet used for Manduca sexta laboratory rearing. To simplify the preparation and to reduce the cost of this diet, a new formulation was developed. Larvae reared on the new agar-based diet achieved higher pupal rearing efficacy than larvae reared on bran diet recently used in medfly mass rearing facilities. Heat treated medflies reared on the new agar-based diet achieved similar pupal rearing efficacy with heat treated medflies reared on bran diet. When testing population density, higher pupal rearing efficacy was again achieved on new diet. The highest pupal rearing efficacy was achieved with 100 eggs per 25 g of diet, lowest with 500 eggs per 25 g of diet. Concerning pupal weight, there was no difference in results achieved on Petri dishes with different larval population densities. Larvae reared on new agar-based diet reached better results than larvae reared on bran diet. The preparation of the new diet is simple and the cost is low, so it is good for laboratory tests and rearing.     

Experience-based behavioral and chemosensory changes in the generalist insect herbivore Helicoverpa armigera exposed to two deterrent plant chemicals

Behavioral and electrophysiological responses of larvae of the polyphagous moth species Helicoverpa armigera to two plant-derived allelochemicals were studied, both in larvae that had been reared on a diet devoid of these compounds and in larvae previously exposed to these compounds. In dual-choice cotton leaf disk and pepper fruit disk arena assays, caterpillars reared on a normal artificial diet were strongly deterred by strychnine and strophanthin-K. However, caterpillars reared on an artificial diet containing strychnine were insensitive to strychnine and strophanthin-K. Similarly, caterpillars reared on an artificial diet containing strophanthin-K were also desensitized to both deterrent chemicals. Electrophysiological tests revealed that the deterrent-sensitive neurons in taste sensilla on the maxillae of caterpillars reared on each deterrent-containing diet displayed reduced sensitivity to the two chemicals compared with the caterpillars reared on normal diets. We conclude that the experience-dependent behavioral plasticity was partly based on the reduced sensitivity of taste receptor neurons and that the desensitization of taste receptor neurons contributed to the cross-habituation to the two chemicals.     

Patterns and mechanisms of growth of fifth-instar Manduca sexta caterpillars following exposure to low- or high-protein food during early instars.

For many insect herbivores, variation in protein availability is a pervasive part of the environment. I explore how variable protein availability affects growth rates of fifth-instar Manduca sexta caterpillars and how growth is related to behavior and physiology. Groups of larvae were reared on low- or high-protein artificial diets (5.9% and 17.7% casein by dry weight, respectively) and then transferred in the fifth instar to the same or opposite diet. During or after the 24-h period following transfer, I measured growth rate, consumption rate, growth efficiency, midgut proteolytic activity, and masses of midgut contents and tissues. Fifth-instar caterpillars reared in earlier instars on high-protein diet grew about 20% more rapidly over 24 h than did caterpillars reared on low-protein diet. This growth pattern appears to be caused by differences in consumption and growth efficiency: caterpillars reared on high protein consumed more food, and used it more efficiently, than did caterpillars reared on low-protein diet. Over the short term (24 h), in contrast, fifth instars that received low-protein diet grew as rapidly as caterpillars that received high-protein diet. Increased (compensatory) consumption appears to be the primary mechanism by which caterpillars consuming low-protein food maintained growth rates.     

幼虫密度对甜菜夜蛾生长发育与繁殖的影响

为了研究甜菜夜蛾Spodoptera exigua(Hübner)幼虫的密度对其发育及繁殖的影响,本实验观察了5种幼虫密度下（1,5,10,20,30头/瓶）,幼虫发育和成虫繁殖情况。结果表明：幼虫和蛹历期、存活率和蛹重均差异显著。幼虫和蛹历期均以20头/瓶的最短,1头/瓶的最长,其余随幼虫密度增加而延长;幼虫至蛹存活率以10头/瓶的最高,其余随幼虫密度增加而降低;1头/瓶的蛹最重,显著高于其他密度的,其余随幼虫密度增加而下降。尽管密度间成虫羽化率和产卵前期均无显著差异,但成虫产卵量、寿命和畸形率差异显著。1头/瓶的产卵量最多,其次为10头/瓶的,其余随幼虫密度增加而减少,30头/瓶的产卵量显著少于其他密度的; 密度在1～20头/瓶范围内,雌蛾寿命均较短,显著短于30头/瓶的,而雄蛾寿命以5头/瓶的最短,显著短于其他密度的（10头/瓶除外）,10头/瓶的次之,其余密度间差异不显著;不同幼虫密度下羽化的成虫畸形率差异显著,10头/瓶的最低,其余随幼虫密度增加而升高; 生命表结果表明甜菜夜蛾在10头/瓶下世代存活率和种群增长指数均最高,幼虫密度过低或过高均不利于种群增长;世代存活率（S）和种群增长指数（I）与幼虫密度之间的关系均呈抛物线关系：S =－0.2087x²+2.5694x+211.52 (R²=0.88),I=－0.0552x²+0.9166x+54.168 (R²=0.95)。结果提示幼虫密度影响甜菜夜蛾种群动态的重要生态因子之一。     

Rearing of ectoparasitoid Diapetimorpha introita on an artificial diet: supplementation with insect cell line-derived factors

We investigated the use of two insect cell lines to improve an artificial diet (DI) for the pupal ectoparasitoid Diapetimorpha introita. DI was supplemented with Grace's culture medium conditioned with IPL-LdFB, a cell line derived from fat body of the gypsy moth, Lymantria dispar (FBCell diet), and with Grace's medium conditioned with Sf9, a cell line derived from ovaries of the fall armyworm, Spodoptera frugiperda (Sf9Cell diet). The diets were also chemically analyzed for nutrients and any deficiencies were filled by the addition of nutrients. One-half ml aliquots of each diet were encapsulated in paraffin domes and newly hatched larvae of D. introita were placed on each diet (one larva/dome) and allowed to develop to the adult stage. Providing fresh diet on day four when the larvae were in the third instar did not improve parasitoid production. Compared with DI, only Sf9Cell had a positive effect on the parasitoid's growth, increasing the size of male parasitoids. The parasitoids, however, took longer to develop to the adult stage than those reared on the natural host. Neither cell line significantly enhanced the average weight of female parasitoids, shortened developmental time, nor increased % cocoons produced and % adult emergence. Providing additional nutrients (amino acids, vitamins, cations and anions, fatty acids and milk/egg protein) to both diets (based on chemical analyses of the cell line-supplemented diets) enhanced the average weight of the females on Sf9Cell and males and females on FBCell. The nutritional additions, however, did not improve the developmental time, pupation and adult emergence.     

不同食物对甜菜夜蛾生长发育参数的影响

选择上海地区近年甜菜夜蛾Spodoptera exigua(Hübner)发生比较严重的甘蓝、豇豆、大葱、芦笋4种寄主植物,在温度(27±1)℃,相对湿度70%±5%,光照L:D=14:10的条件下研究了不同寄主植物对甜菜夜蛾发育特征的影响。结果表明,不同寄主植物饲喂甜菜夜蛾,甜菜夜蛾幼虫发育历期、存活率、蛹重、成虫寿命、净生殖力和内禀增长率等参数在寄主植物间有显著差异。用甘蓝饲喂的甜菜夜蛾雌虫产卵量明显高于取食大葱和芦笋的。同样,取食甘蓝的甜菜夜蛾蛹重、净生殖力和种群内禀增长率等参数明显高于取食大葱和芦笋的,说明甘蓝与其他寄主植物相比提供了较好质量的食物。     

Effects of varying levels of dietary vitamin E (α‐tocopherol) on growth performance,proximate and fatty acid composition of juvenile silver pomfret (Pampus argenteus Euphrasen, 1788)

This study investigated the effects of elevated dietary levels of vitamin E (α‐tocopherol) on growth performance, proximate composition and fatty acid profiles of juvenile silver pomfret, Pampus argenteus. Three semi‐purified experimental diets were formulated to contain 49% protein and 16% lipid. High docosahexaenoic acid (DHA) tuna oil was added to the diets to supplement DHA. A graded level of vitamin E (0‐, 50‐, and 100 mg kg^?1) was added to experimental diets 1 to 3, respectively. Analyzed vit. E levels were 155.2, 195.3 and 236.4 mg kg^?1 in diets 1, 2 and 3, respectively. The experiment was conducted for 12 weeks with juvenile silver pomfret (29.6 ± 7.6 g) using a flow‐through system consisting of nine 1‐m³ tanks. Each treatment had three replicates and fish were stocked at the rate of 20 m^?3. Growth performance and feed utilization parameters of fish fed diets 2 and 3 were significantly (P < 0.05) higher than in fish fed diet 1, but the parameters in diets 2 and 3 did not differ significantly (P > 0.05). Although whole body protein levels were not influenced by the dietary vit. E levels, whole body lipid in fish fed diet 2 was significantly higher than in fish fed the other diets. The whole body vit. E levels in fish fed diet 2 (22.6 mg kg^?1) and diet 3 (24.1 mg kg^?1) were significantly (P < 0.05) higher than in those fed diet 1 (18.2 mg kg^?1). Whole body total saturated fatty acids were significantly lower, and DHA levels higher in fish fed diets 2 and 3 than those fed diet 1. The results of the present study suggest that increasing dietary supplementation of vit. E in high lipid diets enhances the growth performance of fish and that a dietary level of 196 mg kg^?1 vit. E is suitable for the growth of silver pomfret.     

Effects of linear furanocoumarins on the herbivore Spodoptera exigua and the parasitoid Archytas marmoratus: host quality and parasitoid success

We assessed the effects of three photoactivated linear furanocoumarins, secondary plant metabolites present in Apium spp. (Apiaceae) and other taxa, on the larval-pupal parasitoid, Archytas marmoratus (Townsend) (Diptera: Tachinidae) and the host Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), in the presence and absence of ultraviolet radiation. These results then were compared with previously described responses of Archytas marmoratus and other hosts to different plant allelochemicals. Ultraviolet radiation had no consistent detrimental effects. Increasing concentrations of linear furanocoumarins (from 0 to 0.029% of fresh weight) increased mortality of both the host and parasitoid. Increasing linear furanocoumarin levels also prolonged larval development of surviving S. exigua, but had no effect on pupal developmental time or pupal mass. Consequently, there was no effect of increasing linear furanocoumarin levels on surviving parasitoid development time (from the time of host pupation) or size. These results indicate the effects of linear furanocoumarins are mediated through effects on the host. Because reported responses of Ar. marmoratus to other allelochemicals (e.g., flavones, methyl ketones) are mediated through host effects, these results support the hypothesis that Ar. marmoratus displays a generalized response to plant allelochemicals that are predictable based on host mediated effects.     

Three hundred and fifty generations of extreme food specialisation: testing predictions of nutritional ecology

We used a strain of diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), that had been reared for approximately 350 generations in a precisely characterised environment to test hypotheses regarding the influence of nutritional heterogeneity on the evolution of nutrient regulatory responses. Caterpillars were maintained with ad libitum access to a diet that emulated that of an extreme nutritional specialist, comprising a homogeneous food of fixed nutrient composition. We measured performance (survival, development rate, and pupal mass), as well as the protein and carbohydrate intake of individual caterpillars confined to one of a range of single foods differing in their protein, carbohydrate, and water content. In a separate experiment, we measured the amount and balance of protein and carbohydrate self-selected by caterpillars presented with nutritionally complementary foods. Results showed a close fit with three of four predictions about the nutritional responses of 'nutrient specialist' feeders: (1) survival, development rate, and pupal mass were highest for animals given diets with the protein:carbohydrate composition of the ancestral culture diet, and dropped off sharply with higher and lower protein:carbohydrate balance, (2) caterpillars coped poorly with dietary dilution by water, irrespective of the macronutrient balance, and (3) the self-selected intake point corresponded with the macronutrient balance that gave peak performance (i.e., that of the ancestral culture diet). The fourth prediction, that caterpillars would be disinclined to over-ingest nutrients on imbalanced diets, was at best weakly met. We hypothesise that the evolution and maintenance of the specialist strategy might, paradoxically, require some degree of environmental heterogeneity.     

Effect of dietary nitrogen on gypsy moth larval nutritional indices, development and lipid content

Nutritional indices, development rates, percent dry weights and total lipids were determined in gypsy moth larvae (Lymantria dispar L.) reared on a high wheat germ (HWG) diet or diets prepared from lyophilized, ball-milled oak or pine foliage as the only source of dietary nitrogen (N). With regard to both total and proteinaceous N content, HWG diet>oak diet>pine diet. All nutritional indices measured were significantly lower in second instars fed pine diet vs. oak diet. Protein supplementation of pine diet with either casein or ovalbumin to bring total N up to the level present in oak diet resulted in small increased in approximate digestibility (AD) and effciency of conversion of ingested food (ECI), but relative growth rate (RGR) remained unaffected. The low RGR of larvae fed pine diet (unsupplemented or protein supplemented), as compared to those fed HWG or oak diet, was accompanied by significantly lower larval percent dry weight and percent total lipid. In contrast, RGR, larval percent dry weight and total lipid values were comparable in second instars fed HWG or oak diet. Insects reared from the first through the final instar on oak diet exhibited lower pupal weights compared to those reared on HWG. Casein addition to oak diet generally resulted in even more extended larval development times and further reduced pupal weights, but wheat germ addition to oak diet did not alter development rates and caused an increase in pupal weights.