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.     

Effects of dietary variation on growth,composition, and maturation of Manduca sexta (Sphingidae: Lepidoptera)

Most studies linking dietary variation with insect fitness focus on a single dietary component and late larval growth. We examined the effects of variation in multiple dietary factors over most life stages of the sphingid moth, Manduca sexta. Larvae received artificial diets in which protein, sucrose, and water content were varied. The relationship between larval size, growth and consumption rates differed significantly across diets. Larvae on control and low-sucrose diets grew most rapidly and attained the largest pupal and adult sizes. Conversely, larvae on low-water and low-protein diets initially grew slowly, but accelerated in the fifth instar and became pupae and adults comparable to control animals in size. There were no fundamental differences in protein:carbohydrate consumption patterns or strategies among experimental diets and larval instars. However, inadequate dietary water appeared to be more important for early than late instar larvae. Larvae on all artificial diets showed increasing fat content throughout all stages, including wandering and metamorphosis. Compensatory feeding among low-water and low-protein larvae was correlated with significantly higher fat content in larvae, pupae and adults, whereas low-sucrose animals were substantially leaner than those on the control diet. These differences may have strong effects on adult physiology, reproduction, and foraging patterns.     

Diet-switching by gypsy moth: effects of diet nitrogen history vs. switching on growth, consumption, and food utilization

Gypsy moth (Lymantria dispar (L.) (Lepidoptera: Lymantriidae)) larvae were reared from hatch on 1.25% N or 3.5% N artificial diet (previous diet) and switched reciprocally to the other diet (current diet) after molting into the second, third, fourth, or fifth instar. The nitrogen concentration of food consumed during previous instars had a strong residual effect on the growth rate in subsequent instars when a diet switch was made during instars two through four, but did not affect growth rate of fifth-instar larvae despite effects on food consumption and utilization. In early instars, larvae reared on 1.25% N artificial diet and then switched to 3.75% N diet had lower mass-adjusted growth rates than larvae continuously reared on 3.75% N diet. Conversely, larvae reared on 3.75% N diet and switched to 1.25% N had higher mass-adjusted growth rates than larvae reared continuously on 1.25% N diet. Relative to larvae previously reared on 1.25% N diet, fifth-instar male larvae previously reared on 3.75% N diet had slightly lower consumption rates, higher net growth efficiency (ECD), and higher gross growth efficiency (ECI). Larvae previously reared on 3.75% N diet tended to have lower food assimilation efficiency (AD) and lower nitrogen assimilation efficiency (AD(N)). Although both previous and current diet nitrogen concentration strongly affected larval growth and food utilization, the interaction term between these was not significant for any response variables except ECD and ECI. Because the interaction term reflects the effect of switching per se, the results indicate that there was a metabolic cost associated with switching, but no inherent net cost or benefit of diet-switching to growth.     

Getting a head start: diet, sub-adult growth, and associative learning in a seed-eating passerine

Developmental stress, and individual variation in response to it, can have important fitness consequences. Here we investigated the consequences of variable dietary protein on the duration of growth and associative learning abilities of zebra finches, Taeniopygia guttata, which are obligate graminivores. The high-protein conditions that zebra finches would experience in nature when half-ripe seed is available were mimicked by the use of egg protein to supplement mature seed, which is low in protein content. Growth rates and relative body proportions of males reared either on a low-protein diet (mature seed only) or a high-protein diet (seed plus egg) were determined from body size traits (mass, head width, and tarsus) measured at three developmental stages. Birds reared on the high-protein diet were larger in all size traits at all ages, but growth rates of size traits showed no treatment effects. Relative head size of birds reared on the two diets differed from age day 95 onward, with high-diet birds having larger heads in proportion to both tarsus length and body mass. High-diet birds mastered an associative learning task in fewer bouts than those reared on the low-protein diet. In both diet treatments, amount of sub-adult head growth varied directly, and sub-adult mass change varied inversely, with performance on the learning task. Results indicate that small differences in head growth during the sub-adult period can be associated with substantial differences in adult cognitive performance. Contrary to a previous report, we found no evidence for growth compensation among birds on the low-protein diet. These results have implications for the study of vertebrate cognition, developmental stress, and growth compensation.     

Development and feeding efficiency of Malacosoma neustrium larvae reared with Quercus spp. leaves

Observations on larval development of Malacosoma neustrium were conducted both in a cork oak stand and in the laboratory by using leaves of different host trees (cork oak, holm oak and downy oak) as food source. Instars were determined using head capsule and frass measurements. In the field the larvae progressed up to the fifth instar before pupating, and the increase in head capsule width followed Dyars Rule with a rate of increase (R.I.) value of 1.74. The same number of instars was determined for the larvae reared with cork oak (R.I. = 1.73) and holm oak (R.I. = 1.70) leaves. The caterpillars reared with downy oak foliage completed larval development in five, six and seven instars and the R.I. values obtained were 1.60, 1.52 and 1.44 respectively. A lower mortality was recorded for the larvae reared on holm oak. Growth and feeding indices were determined for the larvae from the third up to the last instar. The highest leaf consumption was detected for the fifth instar larvae reared on holm oak. For the caterpillars which completed five instars before pupating, the relative consumption rate (RCR) decreased from the third up to the fifth instar: from 4.8 to 1.7 (cork oak), from 7.4 to 3.3 (holm oak) and from 14.3 to 2.1 (downy oak). The relative growth rate (RGR) was highest during the fourth stadium (0.24, 0.27 and 0.33 for larvae reared with cork oak, holm oak and downy oak leaves respectively) and decreased in the fifth instar (0.09, 0.14 and 0.14 for larvae reared with cork oak, holm oak and downy oak leaves respectively), probably because of greater expense of energy due to the approach of maturity. Feeding and growth indices could be useful to define a defoliation prediction model.     

Feeding behavior and growth of corn earworm (Lepidoptera: noctuidae) larvae on Bacillus thuringiensis-treated (dipel 4L) and untreated meridic diet

The effect of Dipel 4L in artificial diet on feeding behavior, occurrence on a specific diet, and growth of corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), was assessed in short-term tests. Third-, fourth-, and fifth-stage laboratory-reared and feral corn earworm larvae were evaluated. Arenas used for each assay included a non-Dipel diet, Dipel-containing diet, and a combination of the two diets. Larval activity was observed immediately after exposure to diet and at 6 and 18 h for third instars and at 6, 8, and 24 h for fourth and fifth instars, respectively. Feral and laboratory-reared third, fourth, and feral fifth instars avoided Dipel-treated diet when more suitable food was available. Third and fourth instars consistently preferred non-Dipel-containing diet when presented a choice of foods. Corn earworm growth was delayed when larvae were subjected to Dipel-treated diet in choice and no-choice assays compared with larvae provided untreated diet. Larvae presented a choice of diets grew more rapidly than those presented Dipel-treated diets in no choice arenas. Larval feeding frequency and weight gain were superior when larvae were supplied untreated diet than when restricted solely to a Dipel-treated diet. Larvae presented a choice of diets spent more time feeding and fed more frequently on untreated diet than Dipel-treated food. These data indicate that corn earworm presented a choice of Bacillus thuringiensis (Bt) and non-Bt diets may have an increased probability of completing development compared with those restricted to Bt-laced sources.     

Failure to avoid rutin diets results in altered food utilization and reduced growth rate ofManduca sexta larvae

The possibility of avoidance of and dietary self-selection relative to the flavonol rutin was examined for third instarManduca sexta for two thermal regimes and for larvae previously reared on plain or rutin diet. Temperature affected all of the performance indices examined, except efficiency of conversion of digested food. Significant interactive effects between temperature and diet occurred for relative consumption rate, relative growth rate and the food utilization efficiencies. For example, at the warm daytime temperature, relative growth rate prior to head capsule slippage was lower for caterpillars previously reared on rutin diet compared to those reared on plain diet. In contrast, at the cool daytime temperature, the relative growth rates were similar for caterpillars reared on plain diet and on 6 μmoles rutin diet. Consequently, in some treatments (5 of 12), caterpillars with a history of rutin in their diet had lower relative growth rates than those experiencing rutin for the first time. Despite rutin's impact on food utilization indices and negative effect on relative growth rate, the caterpillars did not avoid rutin nor was there evidence of regulation of the intake of rutin. The lack of metabolic feedback is discussed.     

The influence of temperature transfers on subsequent growth of the European peacock butterfly <Emphasis Type="Italic">Inachis io</Emphasis> (Lepidoptera,Nymphalidae)

The study addresses the effects of higher and lower temperatures experienced during the early stages of ontogeny on the parameters of the subsequent growth and development of the butterfly Inachis io. The caterpillars reared at a temperature of 22°С during instars I–III and then transferred to lower temperatures (16, 18, and 20°C) had higher instantaneous growth rates, larger body mass, and shorter duration of instars IV and V than the caterpillars that developed permanently at these lower temperatures. Vice versa, the caterpillars reared at 16°С during instars I–III and transferred to higher temperatures (18, 20, and 22°C) developed and grew slower than the caterpillars reared at these higher temperatures from the beginning. Possible physiological mechanisms underlying the observed phenomena and their ecological consequences are discussed. Our results are compared with the previously published data on fish—another group of ectothermic organisms, on which similar experiments have been carried out.     

Effects of dietary protein concentration on L-proline transport by Manduca sexta midgut

Foliar protein concentrations vary widely. Phytophagous insects may respond to this variation by regulating the rate of absorption of protein breakdown products. Using fifth-instar Manduca sexta reared on artificial diets, we examined whether the rate of L-proline transport across the posterior midgut was affected by dietary protein concentration. Caterpillars were reared to the fifth instar on a low- or high-protein diet and then transferred to the same or opposite diet for 24 h prior to the flux measurements. Posterior midguts were mounted in Ussing chambers, and both potential difference and (14)C-proline flux across the tissue were measured during two-hour experiments. Midguts transported proline from lumen to hemolymph at about 6.5 &mgr;mol/cm(2)/h and from hemolymph to lumen at less than 0.43 &mgr;mol/cm(2)/h. Only a small fraction was oxidized (0.58 &mgr;mol/cm(2)/h), and proline was not converted to another compound while crossing the midgut epithelium. Neither proline transport rates nor potential differences across the epithelium differed significantly among treatment groups, suggesting that larval M. sexta do not regulate proline transport in response to dietary protein variation.     

Biological, nutritional, and histochemical basis for improving an artificial diet for Bracon hebetor Say (Hymenoptera: Braconidae)

The biology of Bracon hebetor Say (Hymenoptera: Braconidae) reared on fifth instars of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) (natural diet) and in vitro (artificial diet) was evaluated. Data on the number of instars, development time and food intake were collected, and histochemical tests were conducted to detect proteins and lipids in the parasitoid's digestive tract. The data disclosed differences that can help to improve artificial rearing of B. hebetor. B. hebetor had three instars in both diets, but the developmental time on the artificial diets was prolonged due to the increase in larval and pupal development times. Larvae grew faster on the natural host and required a lower food intake (2.7 microl) as compared to that required by the larvae feeding on the artificial diet (3.8 microl). Analysis of diet protein content and host hemolymph and the observations on the parasitoid larvae gut content indicated altogether the artificial diets requires the addition of others sources of proteins and lipids to improve the overall nutrition quality of the in vitro rearing system for this ectoparasitoid.     

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.     

Effects of temperature on growth and efficiency of food utilization in fifth-instar caterpillars of the tobacco hornworm, Manduca sexta

Fifth-instar larvae of Manduca sexta were reared from hatching on artificial diet at 15, 20, 25, 30 and 35°C. Total development time decreased with increasing temperature. Very few larvae (12%) survived at 15°C, so this temperature was not considered further. There was some mortality at 30°C (11%), and at 35°C (50%).The absolute rate of growth in the fifth instar was faster at 25 than at 20°C, but was similar at 25, 30 and 35°C. This was true both for caterpillars that were chronically exposed to experimental temperatures (i.e. since hatching) and for those acutely exposed (i.e. reared up to fifth instar at 25°C).There was a progressive decrease with higher rearing temperatures in both the initial and final sizes of chronically exposed fifth-instar larvae. Acutely exposed caterpillars matched for initial size showed smaller temperature related differences in final size. Because of these size differences there were differences in relative growth rate which did not reflect true differences in absolute growth rate.Total food consumed by chronically exposed caterpillars was greatest at the lowest temperature (20°C), and decreased progressively with increasing temperature. The absolute rate of food consumption increased from 20 to 25°C, but did not vary significantly between 25 and 35°C. Differences in the sizes of the insects at the different temperatures meant that there were differences among relative measures of consumption that did not reflect absolute food consumption.For chronically exposed caterpillars, none of the three usual indices of food conversion efficiency (AD, ECI and ECD) varied significantly with temperature between 20 and 35°C. This implies that the effects of temperature on metabolic costs are closely matched to food consumption.Oxygen consumption increased with temperature between 20 and 25°C but was temperature compensated between 25 and 35°C.These findings are discussed in terms of their implications for the optimal temperature for growth in Manduca.     

Effects of rutin-fed caterpillars on an invertebrate predator depend on temperature

Summary A factorial experiment examined the effects of varying concentrations of the allelochemical rutin in caterpillars and the length of time the caterpillars had fed on the behavioral interactions of predatory stinkbugs (Podisus maculiventris) and their prey (Manduca sexta). Diet had no significant effect on defensive behavior of the caterpillars. The length of time that the caterpillars had fed (1 vs. 24 h) only influenced the frequency of caterpillars knocking the attacking stinkbugs away, with caterpillars knocking the stinkbugs away more often after 24 h of feeding. A second experiment tested the effects of diet (prey fed various concentrations of rutin), temperature (18° C and 28° C) and gender on consumption and growth parameters of fifth instar stinkbugs. At the cooler temperature, the bugs ate more, gained more weight but took twice as long to complete the stadium and consequently had reduced relative consumption and relative growth rates. Diet had no significant effect on biomass gained or stadium duration, but rutin-fed caterpillars did depress the stinkbugs' relative consumption rates. The effect of food quality on relative growth rate (RGR) was temperature dependent; rutin had no significant effect at the cooler temperature, but a high dose of rutin reduced RGR at the warmer temperature. Rutin had a greater negative impact on the females than the males. The effect of rutin on these predators was different than the effect on their prey (this study compared to Stamp (1990, 1992)): the negative effects of rutin seem to impact on the stinkbug's growth rather than on molting.     

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.     

Growth and induction in food consumption of Helicoverpa armigera Hbn. (Lep., Noctuidae) larvae on chickpea, soybean, and maize diets

Laboratory studies were conducted to determine the effect of different artificial diets made of powdered seed materials of chickpea ( Cicer arietinum ), soybean ( Glycine max ), and maize ( Zea mays ) on the growth, consumption, and feeding preferences of Helicoverpa armigera larvae. Food consumption and growth of ultimate instar gram pod borer larvae were minimal on maize diet. The nutritive value of the soybean diet was higher, but the consumption rate of larvae was highest on chickpea diet compared with the other test diets. The growth of larvae was statistically equal on chickpea and soybean diets, in spite of differences in the consumption rate of these diets and their nutritive value. There appears to be a direct correlation between the quantity of the diets consumed and their nutritive value for growth of the larvae on chickpea and soybean diets. The lower nutritive value of chickpea diet is correlated with its higher intake by the larvae. Similarly, the lower consumption rate of larvae on soybean diet is correlated with its higher nutritive value. The diet on which the larvae were fed during earlier instars did not induce any feeding preference for that particular diet in the ultimate larval instar. The larvae consumed similar quantities of each of the three diets in their ultimate instar, irrespective of having fed on any of these diets during any preceding instars. However, induction in the quantitative consumption of food by the larvae was evident. The higher or lower consumption rate of diet by the larvae in the ultimate instar was influenced by their food during earlier instars. Hence the food consumption rate of larvae in the last instar appears to be set while feeding on a diet in the preceding instars.     

Postnatal protein deprivation in rhesus monkeys

We studied the growth of 97 rhesus monkeys (M. mulatta) that from birth until 120 days of age were fed a diet containing 13.4%, 6.7%, 3.35% protein or a commercial simulated human-milk formula (SMA) affording 9% protein. After 120 days, all animals were fed SMA. Females fed the diet lowest in protein, but not the other diets, were moderately affected, gaining less weight than their well-fed counterparts did, but they recovered their deficit during the repletion period, so that at 240 days no group differences remained. Males fed the two lowest-protein diets were severely and profoundly affected, in keeping with the depth of their protein deficiency. Moreover, unlike the females, they recovered none of their weight deficit during the repletion period. Food intake during deprivation was lower in the animals eating the low-protein diets. During SMA repletion, intakes followed no simple rule, but they did not converge. Except for the males fed the 3.35% protein diet, relative food intake (ml formula/kg body weight) did not differ substantially between diets or sexes at any time during the deprivation and diminished as the animals got older. Those males' relative intakes did not decline. During repletion, the SMA females ate the most in proportion to weight and the 13.4% group the least. The lowest-protein males, in contrast, ate the most in proportion to their weight during both deprivation and repletion. Males fed the lowest-protein diet gained little for what they ate; those fed the highest-protein diet gained much. Females were more efficient than males were when eating the low-protein diet and less efficient when eating the high-protein diet. When fed SMA during repletion, males' food efficiencies (grams gained/liter of diet) were nearly equal; females still differed: the SMA group was the least efficient and the low-protein group most efficient. Its counterpart, protein efficiency, was greatest (during deprivation) for females eating the low-protein diet and least (among females) for those eating the high-protein diet. Males were least protein efficient if eating the low-protein diet. Evidently, a 4 month bout of protein deprivation had prolonged effects on the amount of food the animals needed to produce a given gain in weight.     

Contrasting diel activity and feeding patterns of four instars of Rhyacophila dorsalis (Trichoptera)

1. Ontogenetic shifts in prey choice and predator behaviour can affect food‐web structure. Therefore, it is important to establish if the diet and feeding activity differ between life‐stages of the same species. This hypothesis was tested for second, third, fourth and fifth larval instars of Rhyacophila dorsalis by comparing their diel activity and feeding patterns. Second to fifth instars collected from two streams were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks. Food was provided in excess; being organisms living in bryophytes on top of a large stone in each tank, augmented by different‐sized larvae of Ephemeroptera, Simuliidae and Chironomidae. As few first instars for gut analyses were found in the field, the diet of first instars reared in the laboratory was also studied. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 50 larvae per instar for each day or night sample). First and second instars fed on the smaller food items with no significant day‐night differences in diet. Gut contents indicated a progressive trend from feeding chiefly at night in third instars to almost exclusively at night in fifth instars. Fourth and fifth instars fed on the larger food items, whilst the diet of the third instar larvae overlapped with that of both the earlier and later instars. 3. Diel activity patterns of single larvae differed between instars but not within each instar (n = 20 larvae per instar). Second instars were active throughout the 24 h, with peaks at dusk, around midnight, dawn and around midday. A similar pattern was shown by third instars but the peak of activity at midday was less than the other three peaks. Prey were captured only during these peaks for both instars. Fourth and fifth instars were most active, and fed only, at night. They used an ambush strategy to capture more active prey at dusk and dawn (e.g. Baetis, Gammarus), and a searching strategy to capture more sedentary prey during the night (e.g. chironomids, simuliids). These experiments provided support for the hypothesis under test. If competition and/or interference occur between instars, then it could be reduced between earlier and later instars because of differences in their diet and diel pattern of feeding activity.     

Diet influences male-female interactions in the bushcricketRequena verticalis (Orthoptera: Tettigoniidae)

The influence of diet on the courtship roles of male and female Requena verticaliswas investigated in the laboratory. The protein content of available food was found to affect the frequency of mating attempts. Pairs which were fed on a low-protein diet were involved in fewer mating attempts than pairs which were fed on a high-protein diet. Diet also influenced the relative frequencies of male and female rejections. Males rejected their virgin female partners more often than females rejected their male partners when the pairs were kept on a low-protein diet. The opposite was found when the female had mated once before. No difference in the frequency of male and female rejections was found when the pair was kept on a high-protein diet irrespective of the mating status of the female.     

The influence of diet on growth and secretion behaviour of myrmecophilous Polyommatus icarus caterpillars (Lepidoptera: Lycaenidae)

Abstract.

• 1 Caterpillars of the facultatively myrmecophilous butterfly Polyommatus icarus were reared on inflorescences, or foliage, of four natural hostplant species and on an artificial diet to study dietary effects on larval growth and secretory capacity.
• 2 Caterpillars achieved highest weights and relative growth rates when fed flowers of Medicago sativa, Lotus corniculatus or Melilotus officinalis. Larvae reared on Coroniüa varia (flowers and leaves), foliage of M.sativa and on the artificial diet pupated at lower weights and achieved lower growth rates.
• 3 In standardized experiments with the ant species Lasius flavus, secretion rates from the dorsal nectar organ (DNO) were 2 times higher among flower-fed caterpillars than among foliage-fed siblings or caterpillars on the artificial diet. Larvae reared on C.varia flowers were superior to all other food treatments with respect to secretion rates.
• 4 High water content of larval diet, as in flowers, appears to be important for lycaenid caterpillars to achieve high secretion rates, whereas the correlation between myrmecophily and nutrient availability, as evidenced by growth rates, was less pronounced.
• 5 Using experimental data on larval growth and secretion rates, the lifetime volume of secretions from the DNO is estimated to range from 2 to 5 μl in most food treatments. Only on C.varia flowers (5.5–8.7 μl) and on M.sativa leaves (0.9–1.1 μl) did the caterpillars deviate in their absolute investment in myrmecophily.
• 6 The estimated lifetime investment accounted for 1.6–5.5% of prepupal fresh weight in all food treatments except on C.varia flowers (7.8–12.3%).

     

Effects of light availability on host plant chemistry and the consequences for behavior and growth of an insect herbivore

We examined how light availability influenced the defensive chemistry of tomato (Lycopersicon esculentum: Solanaceae). Tomato plants were grown either in full sunlight or under shade cloth rated at 73%. Leaves from plants grown in full sunlight were tougher, had higher concentrations of allelochemicals (chlorogenic acid, rutin and tomatine), and had less protein than leaves from plants grown in shade. We determined how these differences in host plant quality due to light availability affected the behavior and growth of a Solanaceae specialist, Manduca sexta. Both in the greenhouse and in the field, caterpillars on shade-grown plants grew heavier in a shorter amount of time than those on plants that had previously been grown in full sunlight. In contrast, the effects of previous light availability to plants on caterpillar behavior appeared to be minor.To further investigate how light availability to plants influenced herbivore growth, we examined the effects of leaf-powder diets made from tomato leaves of different ages (new, intermediate, or mature) grown in full sunlight or shade on caterpillar performance. Caterpillars fed diets made from plants grown in shade consumed less but grew faster than larvae fed diets made from tomato plants grown in full sunlight. Caterpillars fed diets made from new leaves grew larger in less time than caterpillars fed diets made from intermediate aged leaves. Caterpillars did not survive on the mature leaf powder diets. There were plant-light treatment by larval thermal regime interactions. For example, at 26:15 °C , plant-light treatment had no effect on stadium duration, but at 21:10 °C, stadium duration was prolonged with the full sunlight-new leaf diet compared with the shaded-new leaf diet. In a second diet experiment, we examined the interactive effects of protein and some tomato allelochemicals (rutin, chlorogenic acid and tomatine) on the performance of caterpillars. There were food quality by thermal regime interactions. For instance, at 26:15 °C , neither protein nor allelochemical concentration influenced stadium duration, whereas at 21:10 °C, stadium duration was prolonged with the low protein-high allelochemical diet, which simulated full sunlight leaves. In sum, light availability to plants affected defensive chemistry and protein concentration. The difference in food quality was great enough to influence the growth of a specialist insect herbivore, but the effects were temperature-dependent.