A mixed diet of toxic plants enables increased feeding and anti-predator defense by an insect herbivore

Some insect herbivores sequester plant secondary metabolites (PSMs) for their own defense, raising the interesting possibility that grazing herbivores are defended by combinations of PSMs from different plant species. In this study, we tested the hypothesis that the grazing caterpillar, Grammia incorrupta, deters the ant, Aphaenogaster cockerelli, by eating a mixture of plants containing iridoid glycosides (IGs) and those containing pyrrolizidine alkaloids (PAs), and that this deterrence is greater than that attained by eating either plant alone. This hypothesis was tested against the non-mutually exclusive hypothesis that mixing plants containing PAs with those containing IGs improves growth performance. Caterpillar survival and growth were measured on three experimental diets: a PA plant, an IG plant, and a mixture of the two. We measured the degree of deterrence associated with these, and an additional experimental diet devoid of PSMs at naturally occurring A. cockerelli nests. Caterpillars fed both plants gained more mass than those fed either plant alone, but took longer to develop. These differences were not caused by diet-based variation in growth efficiency, but by eating more food when offered the mixed-plant diet relative to single-plant diets. The mixed diet was shown to provide deterrence to ants, whereas caterpillars fed single-plant diets were not significantly more deterrent than caterpillars that had eaten the PSM-free diet. We hypothesize that enhanced defense results from increased food consumption in response to multiple plant species, perhaps leading to greater PSM sequestration. Through this mechanism, bottom-up and top-down effects may mutually reinforce the grazing dietary strategy.     

Variation in temperature and dietary nitrogen affect performance of the gypsy moth (Lymantria dispar L.)

Abstract. . The independent and interactive effects of temperature and dietary nitrogen content on performance of the gypsy moth (Lymantria dispar L.) were examined. In long-term feeding trials, larvae were reared from egg hatch to pupation on low (1.5%) and high (3.7% dry weight) nitrogen diets, under three temperature regimes. Short-term feeding trials with fourth instars and the same treatments were conducted in order to calculate nutritional indices.
Higher temperatures did not influence larval survival and marginally increased final pupal weights, but strongly decreased long-term development rates. They also accelerated short-term growth and consumption rates, and tended to improve food processing efficiencies. High concentrations of dietary nitrogen increased survival rates and final pupal weights markedly, but decreased long-term development rates only marginally. A high content of dietary nitrogen also accelerated short-term development and growth rates, reduced consumption rates, and improved food digestibility. Insects responded to low nitrogen-content diets primarily by eating faster, rather than by altering efficiency of nitrogen use. In the short-term feeding trials, thermal regime and dietary nitrogen interacted to influence growth rates, overall food processing efficiencies and nitrogen consumption rates. No interactive effects were observed in long-term studies.
This research demonstrates that small changes in thermal regime and ecologically relevant variation in dietary nitrogen content can strongly affect gypsy moth performance. Moreover, various performance parameters are differentially sensitive to the direct and interactive effects of temperature and diet.     

新烟碱类杀虫剂拌种对马铃薯甲虫幼虫食物利用和生长发育的影响

为研究马铃薯甲虫Leptinotarsa decemlineata（Say）幼虫取食新烟碱杀虫剂噻虫嗪和吡虫啉处理（有效成分18 g/100 kg种薯拌种）播种90 d后马铃薯叶片的消化吸收和生长发育情况,在室内采用重量法测定了幼虫取食量、体重增加量、食物利用率,近似消化率以及蛹重等营养指标。 结果表明：70%噻虫嗪种子处理可分散粉剂拌种后,马铃薯甲虫幼虫的取食量、体重增加量、食物利用率、食物转化率、近似消化率和相对生长率以及蛹重显著低于10%吡虫啉可湿性粉剂拌种和空白对照（P＜0.05）,发育历期显著长于10%吡虫啉可湿性粉剂拌种和空白对照（P＜0.05）;而10%吡虫啉可湿性粉剂拌种后,马铃薯甲虫幼虫的取食量和3～4龄期的体重增加量与空白对照差异显著（P＜0.05）,蛹重、1～2龄幼虫的体重增长量、食物利用率、食物转化率、近似消化率、相对生长率和生长发育历期与空白对照差异不显著（P＞0.05）。 说明70%噻虫嗪种子处理可分散粉剂拌种对马铃薯甲虫幼虫的取食有显著抑制作用,不能很好地满足其生长发育营养物质的需要,幼虫取食其叶片后,近似消化率和相对生长速率显著降低,生长发育历期显著延长。 这有利于减少当季世代数,降低危害。     

Do changes in dietary chemistry during ontogeny affect digestive performance in adults of the herbivorous rodent Octodon degus?

We characterize the flexibility in digestive performance in degus (Octodon degus) an herbivorous rodent. We tested the hypothesis that dietary and physiological-digestive flexibility are correlated. Degus were fed with artificial diets of different chemical composition from weaning to adulthood and their digestive performance was measured through records of apparent digestibility. The starch content of the acclimation diet was not correlated with protein digestibility nor was it correlated with starch digestibility. In addition, digestive tract morphology was not affected by dietary treatments. Hence, an absence of morphological and physiological flexibility related to digestive traits was observed in degus. The lower flexibility in digestive performance given by our dietary experimental treatments of degus, may be an evolutionary constraint related to their specialized herbivorous food habits.     

Nutrient utilization by caterpillars of the generalist beet armyworm, Spodoptera exigua

Abstract.  Beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), caterpillars are destructive crop pests responsible for considerable annual economic losses. These generalist herbivores are challenged with a diversity of dietary choices that can impact their survival, development and fecundity. In the present study, dietary choices of S. exigua caterpillars, based on the protein to digestible carbohydrate (P : C) ratio of the food, and the impact of nutritionally unbalanced foods on caterpillar performance are assessed. In choice experiments, individual third-instar caterpillars are offered simultaneously a P-biased and a C-biased food until pupation. Caterpillars feed nonrandomly and select a slightly P-biased diet (22P : 20C). In no-choice experiments, second instar caterpillars are reared until pupation on diets ranging in P : C ratio from extremely P- to extremely C-biased. High mortality and delayed development are observed on the C-rich, P-poor diets, highlighting the potential deleterious effects of excess carbohydrates and the importance of protein for growth and development. Diet-dependent differences in pupal weight or pupal lipid reserves are not observed. This contrasts with closely-related Spodoptera species where pupal mass and lipid stores increase on C-rich, P-poor diets. On the extremely P-biased diet, performance is similar to that of individuals reared on the self-selected diet, suggesting that these caterpillars may efficiently be deaminating excess amino acids to generate carbon skeletons, which are shunted into lipid biosynthesis. Spodoptera exigua caterpillars exhibit flexible and efficient pre-ingestive nutrient intake regulation and post-ingestive utilization, allowing these generalist feeders to cope with the heterogeneous diets they may encounter.     

重金属污染影响植食性昆虫的研究进展

重金属污染是世界各国面临的最为棘手的问题之一,对生态系统和食品安全构成了严重威胁。作为生态系统中食物链和食物网的重要环节,植食性昆虫是环境中重金属迁移、积累的重要媒介,其因重金属污染而受到的影响引起了大家的关注。本文综述了从2007至2018年重金属污染对植食性昆虫影响的研究进展。昆虫受重金属胁迫的研究途径有人工饲料添加、野外田间暴露、“土壤-植物-昆虫”食物链传递以及体外注射等。积累在植食性昆虫体内的过量重金属可导致其存活率、繁殖力和种群增长率降低,生长发育迟缓。重金属污染对植食性昆虫的生理生化毒性包括细胞超微结构破坏和DNA损伤,体内能量物质含量降低,酶活性、基因表达改变等。植食性昆虫会通过重金属硫蛋白、解毒酶活性的诱导等机制抵御重金属的毒害,从而对低浓度、长期重金属暴露产生生态适应性,甚至提高对其他逆境(如农药等)的耐受性。     

Phenotypic variation in food utilization in an outbreak insect herbivore

The effects of nutrition may have subtantial impact on insect evolution by shaping different components of phenotypes. The key to undestanding this evolutionary process is to know how nutritional condition affects additive and nonadditive components of the phenotype. However, this is poorly understood in outbreaking insects. We investigated the additive and nonadditive variation present in food utilization traits in spruce budworm individuals subjected to chronic nutritional stress. A total of 160 full‐sib families of spruce budworm (Choristoneura fumiferana Clem.) were raised under laboratory conditions, feeding on 2 diets (high and low energy) during 3 generations. Variables tested were pupal mass, consumption rate (RCR), growth rate (RGR), approximate digestibility (AD), the efficiency of conversion of digested food (ECD) and the efficiency of conversion of ingested food (ECI). Our results show that all traits tested presented a high percentage of nonadditive effects that modulate phenotype expression. We found a significant impact of family × diet interaction on pupal mass, RGR and ECD. Furthermore, these traits exhibited the greatest heritability. There was no evidence of presence of maternal effects. The results revealed that food utilization traits may evolve through epigenetics effects, such as phenotypic plasticity. This information can be used by modellers to improve forecast of spruce budworm population dynamics.     

Phylloplane bacteria increase the negative impact of food limitation on insect fitness

1. When populations of herbivorous insects increase in density, they can alter the quantity or quality of their food. The impacts of diet‐related stressors on insect fitness have been investigated singly, but not simultaneously. 2. Foliage quantity and quality of red alder, Alnus rubra, were manipulated together with the presence of non‐entomopathogenic phylloplane bacteria to investigate their impacts, singly and in combination, on survival, pupal mass, growth rate, fecundity and egg quality of a cyclic forest insect, the western tent caterpillar, Malacosoma californicum pluviale. 3. Food limitation (half food) had strong negative impacts on all life‐history traits. When the larvae were fed continuously, however, neither ingesting phylloplane bacteria nor eating leaves from damaged branches (induced foliage) affected survival. In the half‐food treatment, ingesting bacteria further increased mortality, while feeding on induced foliage improved survival. 4. Growth rate and pupal mass of both sexes were reduced for larvae with food limitation compared with continuously fed insects and this was exacerbated when the larvae also ate bacteria‐treated leaves. A combination of bacteria and induced foliage also reduced larval growth rate by 5% in the full‐food treatment. 5. Fecundity (eggs per egg mass) was 2.7 times greater in full‐food than in food‐limited treatments but neither phylloplane bacteria nor plant induction had an effect. Insects fed induced foliage produced smaller eggs. Overall, there was no evidence of a three‐way interaction between the three stressors, although there were negative synergistic effects, primarily between food limitation and the ingestion of phylloplane bacteria.     

Food preferences and the value of animal food for the carabid beetle Amara similata (Gyll.) (Col., Carabidae)

Abstract:  Several studies have shown that the mainly granivorous carabid beetles, e.g. Amara spp., include animal food in their diet to a considerable extent. We therefore hypothesized that the performance of these beetles would be enhanced by dietary mixing including both seeds and animal food. In order to test this, we conducted laboratory feeding experiments with adults and larvae of Amara similata . Both adults and larvae were subjected to different diet treatments including: seeds, houseflies, grasshoppers, earthworms, slugs and snails in pure and mixed diets. Larval survival, development time, pupal and teneral weights were used as indicators of food quality for the larvae. For the adult beetles, mass change was used as an indicator of food quality. We found seeds to be high-quality food, while all pure animal diets were of low quality for both adults and larvae. Animal foods added to the seed diet had both positive and negative effects. A mixed diet of all foods enhanced the mass gain of adults compared with the seed diet, but reduced larval performance dramatically. Earthworms and grasshoppers added to seeds increased the pupal and teneral weights, while reduced larval survival. Thus, A. similata is omnivorous with a mainly granivorous feeding habit. It may gain benefits on some fitness parameters and incur costs on others from preying or scavenging on animal food. Therefore, the overall fitness consequences of a mixed seed-animal diet are uncertain.     

Mixed artificial diets enhance the developmental and reproductive performance of the edible grasshopper, <Emphasis Type="Italic">Ruspolia differens</Emphasis> (Orthoptera: Tettigoniidae)

Diet mixing is a common feeding habit among polyphagous insect herbivores and is believed to be advantageous for performance-related factors like growth, survival and oviposition. However, relatively little is known about the influence of artificial diet or their mixtures on the performance of edible insects. We examined the effects of artificial diet mixtures on the developmental and reproductive performance (survival, developmental time, fresh adult weight and female fecundity) of an edible grasshopper, Ruspolia differens (Orthoptera: Tettigoniidae). We raised individuals from eggs and reared newly hatched nymphs to adult stage on six different dietary treatments consisting of a single diet, and mixtures of two, three, five, six and eight artificial diets. More diversified diets resulted in shorter development time and greater adult fresh weight and female fecundity compared to the single diet or less diversified diets. Even with slight diet diversification, survival to adult stage was greatly improved. Overall, these results highlight the potential of diet mixtures in achieving maximum adult weights and female fecundity and shortening development time, information which could be used when designing mass-rearing programs for this edible grasshopper.     

When do herbivorous insects compete? A phylogenetic meta‐analysis

When herbivorous insects interact, they can increase or decrease each other's fitness. As it stands, we know little of what causes this variation. Classic competition theory predicts that competition will increase with niche overlap and population density. And classic hypotheses of herbivorous insect diversification predict that diet specialists will be superior competitors to generalists. Here, we test these predictions using phylogenetic meta‐analysis. We estimate the effects of diet breadth, population density and proxies of niche overlap: phylogenetic relatedness, physical proximity and feeding‐guild membership. As predicted, we find that competition between herbivorous insects increases with population density as well as phylogenetic and physical proximity. Contrary to predictions, competition tends to be stronger between than within feeding guilds and affects specialists as much as generalists. This is the first statistical evidence that niche overlap increases competition between herbivorous insects. However, niche overlap is not everything; complex feeding guild effects indicate important indirect interactions.     

Food selection and nutritional ecology of woodlice in Central Chile

Abstract.  Phenotypic flexibility in food selection and digestive efficiency in response is examined in relation to variations in food quality in a detritivorous species of Mediterranean ecosystems, the woodlouse Porcellio laevis Latreille (Isopoda: Oniscidea). It is hypothesized that diet selection should show a positive correlation between diet quality and digestive efficiency. The studied plants are isocaloric but exhibit significant differences in terms of nitrogen, carbon and fibre content. The observations appear to support the hypothesis that these isopods show compensatory feeding behaviour when feeding on poor diets. Contrary to expectation, a dietary effect on relative growth rate is not observed. It is concluded that behavioural skills associated with diet selection and physiological flexibility may allow P. laevis to satisfy and maintain equivalent nutritional levels during exposure to different diet qualities. In general, it appears that physiological flexibility plays an important role in determining nutritional balance in P. laevis , which can be of great benefit in the highly seasonal environment that it inhabits.     

Dietary differences between neighboring Cebus capucinus groups: local traditions, food availability or responses to food profitability?

The feeding patterns of three neighboring groups of Cebus capucinus were documented over a 3-year period in Santa Rosa National Park, Costa Rica. We describe the diets of the three groups and examine whether dietary differences between groups could be attributed to environmental differences in food abundances, to differences in the profitability of what was available or to learned local traditions. Diets were variable among groups; group A primarily ate fruit (81.2% of feeding time) and spent little time eating insects (16.9%), while group C was more heavily reliant on insects (44.3%) and ate less fruit (53.0%). Group B had a diet that was somewhat intermediate (69.8% fruit, 29.0% insects). By measuring the densities of all major plant foods, we were able to determine that many of the dietary differences between groups could not be attributed to simple measures of food abundance, but we could not distinguish between the food profitability hypothesis and local tradition hypothesis.     

Effects of larval density and food stress on life‐history traits of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae)

High population density and nutrition restriction can lead to phase variation in morphology and development, and subsequently induce changes in the reaction norms of adult flight in migrant insects. However, response of migratory propensity to such stress in Endopterygote insects, especially in several species of Lepidoptera, remains unclear. In this study, larval and adult developmental responses to crowding and food stress were investigated in the migratory moth, Cnaphalocrocis medinalis (Guenée). A high larval rearing density significantly reduced pupal mass, survival rate and female fecundity. Larvae developed rapidly under crowding conditions, and time to pupation was 2 days earlier than individuals reared alone. By contrast, short‐term starvation and associated compensatory growth prolonged larval duration by 3–4 days and pupal duration by 1–2 days. It also reduced the pupal mass, but showed no detectable effects on female reproductive performance. Both sexes had similar development strategies; however, females seemed to be more sensitive to crowding and food shortage than males. A positive effect was expected if such stress factors acted as cues that triggering a behavioural or physiological shift to a distinct migratory phase. To the contrary, we found no proof that crowding and starvation caused maturation delay in female reproductive development. All treatments did not significantly increase female pre‐oviposition period. Therefore, we concluded that life developmental responses to crowding and food shortage in this species were different. Adult migration propensity was not enhanced under such stress conditions during the larval phase.     

Temperature and food quality effects on growth,consumption and post-ingestive utilization efficiencies of the forest tent caterpillar Malacosoma disstria (Lepidoptera: Lasiocampidae)

Temperature and food quality can both influence growth rates, consumption rates, utilization efficiencies and developmental time of herbivorous insects. Gravimetric analyses were conducted during two consecutive years to assess the effects of temperature and food quality on fourth instar larvae of the forest tent caterpillar Malacosoma disstria Hübner. Larvae were reared in the laboratory at three different temperatures (18, 24 and 30 degrees C) and on two types of diet; leaves of sugar maple trees Acer saccharum Marsh. located at the forest edge (sun-exposed leaves) or within the forest interior (shade-exposed leaves). In general, larvae reared at 18 degrees C had lower growth rates and lower consumption rates than larvae reared at the warmer temperatures (24 and 30 degrees C). Moreover, the duration of the instar decreased significantly with increasing temperatures. Type of diet also affected the growth rates and amount of food ingested by larvae but did not affect the duration of the instar. Larvae fed sun-exposed leaves consumed more food and gained higher biomasses. Values of approximate digestibility and efficiency of conversion of ingested food were also higher when larvae were fed sun-exposed leaves. Higher growth rates with increasing temperatures were primarily the result of the shorter stadium duration. The higher growth rates of larvae fed sun-exposed leaves were possibly the result of stimulatory feeding and consequently greater food intake and also a more efficient use of food ingested. This study suggests that the performance of M. disstria caterpillars could be enhanced by warmer temperatures and higher leaf quality.     

Interactions of temperature and dietary protein concentration in growth and feeding of Manduca sexta caterpillars

Abstract .Temperature and the protein content of food affect rates of consumption and growth in herbivorous insects in different ways: reduced temperature typically reduces both consumption and growth rates, whereas reduced dietary protein typically increases consumption rate but either reduces or has no effect on growth rate. The interactions between temperature and dietary protein concentration in affecting consumption, growth and efficiency in fifth-instar caterpillars of Manduca sexta were studied, using both short-term (4 h) and long-term (duration of fifth stadium) experiments. The short-term experiments examined constant temperatures between 14 and 42°C, whereas the long-term experiments examined constant temperatures between 18 and 34°C; both experiments considered two levels of dietary protein. In both experiments, caterpillars had significantly higher consumption and frass production rates on low-protein compared with high-protein diets at each test temperature between 18 and 34°C, thereby compensating for the lower diet quality. In contrast, at more extreme temperatures (14 and 42°C) in the short-term studies, consumption and frass production rates were lower on low-protein compared with high-protein diets. As a result, there were substantial interactions between temperature and dietary protein for consumption and frass production rates in the short-term experiments, but not in the long-term experiments. These results suggest that interactions between temperature and dietary protein may emerge because of the failure of compensatory feeding responses at low and high temperatures. It is hypothesized that the failure of compensatory responses is more likely to occur under diurnally fluctuating temperatures than under a constant temperature with the same mean, and it is proposed that interactions between temperature and dietary protein for consumption are relevant to M. sexta and other caterpillars that experience wide diurnal fluctuations in temperature in the field.     

Compensatory dietary selection occurs in larval Locusta migratoria but not Spodoptera littoralis after a single deficient meal during ad libitum feeding

ABSTRACT Final instar nymphs of Locusta migratoria (L.) and larvae of Spodoptera littoralis (Boisduval) were given an artificial diet deficient in either protein or digestible carbohydrate for a single meal during ad libitum feeding, after which they were provided with a choice of two diets, one containing protein but no digestible carbohydrate and the other containing carbohydrate but no protein. Detailed analyses of feeding behaviour showed that locusts exhibited a degree of compensatory dietary selection following the single deficient meal. No such response was evident for the caterpillars, although previous work (Simpson et al. , 1988) has demonstrated that compensatory selection behaviour is marked in this species after periods of 4 h or more on the same deficient diets. These results show that locusts are able to respond extremely rapidly to the nutritional quality of their food by utilizing nutritional feedbacks. This capability may have important implications for the study of foraging strategies in other herbivorous insects.     

Developmental responses to variable diet composition in a butterfly: the role of nitrogen,carbohydrates and genotype

Understanding the evolution of herbivore–plant interactions requires detailed information on proximate responses to relevant dietary variability and genetic variance, if any, associated with these responses. We measured the behavioral and developmental responses of Pieris rapae larvae to variation in the nitrogen (N) and carbohydrate (CARB) content of chemically‐defined diets, using differences in the average responses of sibling groups to estimate underlying genetic variance. Larval P. rapae responded to dietary reductions in both N and CARB with increased feeding, but these responses were inadequate to compensate for dietary N deficiencies within the range of N found in host plants. As a result, larvae on reduced N diets exhibited lower relative growth rates and longer development times, whereas larvae on reduced CARB diets maintained normal developmental trajectories. We also report evidence for genetic variation underlying (a) compensatory feeding responses to CARB and N availability, (b) N‐driven variation in growth rate and (c) CARB‐driven variation in larval duration. Our results highlight N availability as a key factor in the growth and development of this herbivorous butterfly, with CARB availability being less constraining and sufficiently addressed by changes to larval consumption rate. Furthermore, our study reveals standing genetic variance associated with larval responses to macronutrient availability, suggesting continued potential for herbivore–plant co‐evolution in this system despite a putative history of strong directional selection.     

Dietary phosphorus affects the growth of larval Manduca sexta

Although phosphorus has long been considered an important factor in the growth of diverse biota such as bacteria, algae, and zooplankton, insect nutrition has classically focused on dietary protein and energy content. However, research in elemental stoichiometry has suggested that primary producer biomass has similar N:P ratios in aquatic and terrestrial systems, and phosphorus-rich herbivores in freshwater systems frequently face phosphorus-limited nutritional conditions. Therefore, herbivorous insects should also be prone to phosphorus limitation. We tested this prediction by rearing Manduca sexta larvae on artificial and natural (Datura wrightii leaves) diets containing varying levels of phosphorus (approximately 0.20, 0.55, or 1.2% phosphorus by dry weight). For both artificial and natural diets, increased dietary phosphorus significantly increased growth rates and body phosphorus contents, and shortened the time to the final instar molt. Caterpillars did not consistently exhibit compensatory feeding for phosphorus on either type of diet. The growth and body phosphorus responses were not explicable by changes in amounts of potassium or calcium, which co-varied with phosphorus in the diets. Concentrations of phosphorus in D. wrightii leaves collected in the field varied over a range in which leaf phosphorus is predicted to affect M. sexta's growth rates. These results suggest that natural variation in dietary phosphorus is likely to affect the growth rate and population dynamics of M. sexta, and perhaps larval insects more generally.     

Impact of dietary sterols on life-history traits of a caterpillar

Although lepidopteran larvae have been shown to metabolise a number of different phytosterols, their life-history traits in response to these different phytosterols may vary with the species. Using the specialist moth, Plutella xylostella (Linaeus) (Lepidoptera), growth, development and fecundity on artificial diets containing host and non-host phytosterols were measured over two generations. Because of the nature of the experimental design, maternal effects linked to dietary sterol could be assessed. In both generations, survival was highest on diets containing sitosterol as the primary phytosterol. A significant decrease in survival on stigmasterol, a non-host phytosterol, was observed between generations. As expected, survival on a control diet with only trace-sterols decreased between generations. Larval duration and pupal duration in both generations was longest on the diets containing the non-host phytosterols, stigmasterol and spinasterol, and on the trace-sterol diet. Finally, fecundity was affected by dietary sterol. In the first generation, fewer viable eggs were produced on the stigmasterol and trace-sterol diets than on wheatgerm control diet. In both generations, dietary sterol significantly influenced percentage egg viability. Overall, these results indicate that differences in phytosterol structure can have pronounced effects on life-history traits, especially when they are projected to the population level. The implications of these results are discussed with respect to phytosterol use by phytophagous insects and their host plant affiliations.