Gregarious Caterpillars Research Articles

Gregarious caterpillars shorten their larval development time in response to simulated predation threat

Abstract Group living in gregarious caterpillars may shorten the larval stage, which is thought to reduce predation exposure. In the gregarious caterpillar Battus polydamas archidamas (Papilionidae) we addressed the effects of simulated predation threat on the duration of the larval stage in solitary and gregarious caterpillars. We further evaluated the consequences of group rearing and predation stimuli for pupal mass. We reared caterpillars singly and in groups of ten individuals. Caterpillars were subjected to simulated predation threats (prodding with a paintbrush) and control larvae were untouched. We determined larval stage duration and pupal mass. We also recorded in solitary and gregarious caterpillars the proportion of individuals reacting to predation threats with distinct behavioural responses. Caterpillars in the group completed larval development earlier than solitary caterpillars. This pattern of accelerated development was already evident in the first instar. Simulated predation reduced the duration of both the entire larval stage and the first instar, but only for caterpillars in the group. Pupal mass was not affected by the predation treatment in either solitary or gregarious caterpillars. Solitary caterpillars showed thrashing and osmeterium display + thrashing more frequently than gregarious caterpillars, while individuals in the group reacted with osmeterium display to a greater extent. Accelerated larval development in response to predation risk has been predicted by theoretical models, but–to our knowledge–this is the first report on gregarious caterpillars. This putative adaptive response did not entail a fitness cost in terms of pupal mass.

Acoustic stimuli from predators trigger behavioural responses in aggregate caterpillars

AbstractPrey detect their predators through predator signals and cues and, consequently, respond with anti‐predatory behaviours to inhibit the action of their aggressors. Lepidopterans can intercept signals emitted by predators and may defend themselves through chemical, morphological or behavioural responses. In this study, we investigated the effect of acoustic stimuli of different predators on defensive behaviour of gregarious caterpillars. Our results demonstrated that Hylesia nigricans (Lepidoptera, Saturniidae) caterpillars alter their behaviour (i.e. abruptly raising the head) in response to the acoustic stimulus of the predators (i.e. predation risk signals from birds and wasps). The magnitude of this response depended on predator identity and caterpillar body size. Larger caterpillars responded more strongly to predatory stimuli than smaller caterpillars. However, regardless of the size of the caterpillars, they responded more strongly to the stimuli of wasps. In addition, we identified that H. nigricans caterpillars emit ultrasonic noise after detecting the stimuli of the predators – this noise seems to function as an alert about the risk of predation during the early stages of development (second and fifth instars). The duration of ultrasonic emission (i.e. milliseconds) increases with the number of repetitions of the stimuli (i.e. wing‐beat sounds of the wasps and insectivorous birds). These results provide novel information about predation risk in interactions among caterpillars and their predators, and indicate possible communication among invertebrates mediated by the risk of predation.

Immature stages of the Rubiaceae-feeding metalmark butterflies (Lepidoptera: Riodinidae), and a new function for the tentacle nectary organs

Metalmark butterfly (Riodinidae) diversity is heavily concentrated in the Neotropical lowland forests but despite their prevalence basic information on immature stages is still scarce. Here we describe the life cycle of seven taxa in the Rubiaceae-feeding section of the Mesosemiina, including three Mesosemia Hübner, [1819], three Leucochimona Stichel, 1909, and the first information for Semomesia Westwood, 1851. Immature stage morphology of Mesosemia cippus Hewitson, 1859 is described in detail through scanning electron microscopy. Generally, eggs are laid singly and caterpillars are folivorous with a cryptic green coloration except for M. cippus which has gregarious caterpillars with a bright yellow color pattern. Immature stages of all analyzed species are morphologically similar and characterized by: oblate spheroid eggs with small spines on the rib intersections; nonmyrmecophilous larvae with sparse long setae on chalazae or pinnacles, perforated cupola organs (PCOs) and tentacle nectary organs (TNOs) in all instars; pupae attached longitudinally to the substrate by the cremaster and a silk girdle that crosses over abdominal segments A1 or A2. Functionality of the TNOs is documented for the first time in the "Mesosemia section" of the Mesosemiina, but they are not used to facilitate symbiotic interactions between caterpillars and ants. When molested, caterpillars everted the TNOs secreting a conspicuous drop of opaque and viscous liquid with a defensive function. A summary of the host plants in the "Mesosemia section" is presented, confirming the preponderance of oligophagy in the Rubiaceae. The morphological and behavioral traits here described are discussed in the context of defense against natural enemies and constitute key information to understanding the evolution of ant-organs and myrmecophily in riodinids.

Host-plant mediated effects on group cohesion and mobility in a nomadic gregarious caterpillar

Gregarious animals often live in larger groups in food-rich environments. We compare cohesion and mobility of forest tent caterpillar (Malacosoma disstria) groups on high-quality (trembling aspen, Populus tremuloides) and low-quality (sugar maple, Acer saccharum) host trees. Following pheromone trails allows forest tent caterpillars to maintain group cohesion, but can cause groups to become trapped on poor-quality food sources. Trail-following decreases in food-deprived individuals. We combine laboratory and field experiments to show that this nutritionally mediated balance between trail fidelity and exploration generates fission-fusion dynamics, leading to increased mobility and smaller group sizes on poorer quality hosts. Indeed, caterpillar groups feeding on maple spent more time in locomotion, split into smaller groups, switched feeding site more frequently and traveled farther when compared to those feeding on aspen. These fission-fusion dynamics can be explained as an emergent property of individual responses to conspecifics: Individuals drift apart in contexts where responses to cues from conspecifics are weakened. Increased mobility appears as an adaptive response that improves the chances of relocating to a superior food source, but lower group size likely decreases thermoregulation and increases predation. Finally, we show that forest tent caterpillar fission-fusion dynamics not only control the spatial distribution of individuals in a tree, but they are also linked to considerable differences in growth and mortality and therefore can play an important role in population dynamics. Many gregarious animals split up into smaller groups when food is scarce. In many species, the behaviors by which group members stay together and follow each other are well-understood; how then do these behaviors respond to changing conditions? In particular, how does hunger drive groups to split up in response to decreased food availability? We compare mobility and group size of forest tent caterpillar colonies on good- and poor-quality host plants. These caterpillars use pheromone trails to move around together, but when hungry, they tend to leave these trails. We show how caterpillars on a poor-quality host plant are not only more mobile (presumably an adaptive response that improves chances of discovering a better food source), but they also split into smaller groups—a side effect of decreased trail fidelity that possibly exposes them to greater risks.

The impact of leaf-eating caterpillars (Heortia vitessoides) infestation on agar trees in Carita forest research station, Province of Banten

The gregarious caterpillars of Heortia vitessoides Moore is a major defoliator of agar trees. The pest seriously threatens the existing agar tree plantation that has been widely cultivated in the community. Pest attacks began to occur in Indonesia since 2005, resulting in the damage and death of agar tree plants in various regions.To determine the impact of pest attack, a study was conducted through periodic monitoring at agar plantation in Carita Forest Research Station (CFRS), Banten Province, from April 2012 to March 2015. Monitoring was conducted in three plots of agar plantations. Each plot consists of six permanent subplots and in each subplot 15 samples of agar tree were randomly choosen. Data were collected and analyzed on monthly basis according to the intensity of defoliation and the mortality of agar trees. Defoliation intensity was determined by the percentage number of trees suffering defoliation in four damage categories, i.e.: light (10-25%), moderate (25-50%), heavy (50-75%), and severe (75-100%). Tree mortality was calculated as the annual percentage of dead trees. The study showed that the defoliation occurred throughout the year in varying degrees of damage. The monthly percentage of defoliated trees is about 30-70% annualy. The high percentage of tree defoliation mainly occurs during dry and early rainy season (June-December). Higher percentage of heavy and severe defoliations were found mostly at seedling. Repeated heavy defoliation causes stunted growth and tree mortality. Early monitoring and control of pests are very important to be done regularly to prevent the damage wider and heavier.

Trail Marking by Larvae of the Cactus Moth,Cactoblastis cactorum

The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), spends most of its larval life feeding within the cladodes of Opuntia cactuses, but the gregarious caterpillars begin their life outside the plant, and in the later instars make intermittent excursions over plant surfaces to access new cladodes and to thermoregulate. The study reported here showed that when the caterpillars move en masse, they mark and follow trails that serve to keep the cohort together. Artificial trails prepared from hexane extracts of the caterpillar's paired mandibular glands were readily followed by the caterpillars. The glands are remarkably large, and their fluid contents, which constitute approximately 1% of the total wet mass of a caterpillar, are secreted onto the substrate as they move. Although the caterpillars also lay down copious quantities of silk, the material in itself neither elicits trail following nor is it a requisite component of pathways that elicit trail following. Previous analyses of the mandibular glands of other species of pyralid caterpillars showed that they contain a series of structurally distinct 2-acyl-1,3 cyclohexane diones. Chemical analysis indicates that the glands of C. cactorum contain structurally similar compounds, and bioassays indicate that trail following occurs in response to these chemicals. While the mandibular glands' fluids have been shown to act as semiochemicals, effecting both interspecific and intraspecific behavior in other species of pyralids, the present study is the first to report their use as a trail pheromone.

Trail marking by larvae of the cactus moth, Cactoblastis cactorum.

The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), spends most of its larval life feeding within the cladodes of Opuntia cactuses, but the gregarious caterpillars begin their life outside the plant, and in the later instars make intermittent excursions over plant surfac- es to access new cladodes and to thermoregulate. The study reported here showed that when the caterpillars move en masse , they mark and follow trails that serve to keep the cohort together. Artificial trails prepared from hexane extracts of the caterpillar’s paired mandibular glands were readily followed by the caterpillars. The glands are remarkably large, and their fluid contents, which constitute approximately 1% of the total wet mass of a caterpillar, are secreted onto the substrate as they move. Although the caterpillars also lay down copious quantities of silk, the ma- terial in itself neithxer elicits trail following nor is it a requisite component of pathways that elicit trail following. Previous analyses of the mandibular glands of other species of pyralid caterpillars showed that they contain a series of structurally distinct 2-acyl-1,3 cyclohexane diones. Chemical analysis indicates that the glands of C. cactorum contain structurally similar compounds, and bio- assays indicate that trail following occurs in response to these chemicals. While the mandibular glands’ fluids have been shown to act as semiochemicals, effecting both interspecific and intra- specific behavior in other species of pyralids, the present study is the first to report their use as a trail pheromone.

Collective choice of a higher-protein food source by gregarious caterpillars occurs through differences in exploration

Amplification, whereby an individual’s probability of exhibiting a particular behavior increases with the number of conspecifics already performing this behavior, enhances the accuracy and speed of collective decision-making by gregarious animals. However, too strong amplification can lead to the potentially suboptimal selection of the first patch encountered. In eusocial insects (e.g., ants, bees), active recruitment and differential signaling provide a mechanism to avoid this type of collective trap. We use the nomadic gregarious caterpillar Malacosoma disstria to test whether the higher quality of two food sources can be consistently selected in the absence of this type of mechanism. We show that, in this species, neither active recruitment nor differential signaling occur, but that collective choice of the higher quality of two food sources is instead made through differences in exploration. These caterpillars lack flexibility in trail laying, but a reduction in trail following behavior enables them to abandon a poor food source and initiate exploration, forming new trails that are followed by the group. The propensity to leave marked territory and initiate exploration varies with food quality, and increases with decreasing protein content in the food. Indeed, although previous work showed that caterpillar groups can become trapped on a poor-quality protein-only food, we show that they abandon a similarly poor-quality low-protein food and relocate to a more nutritionally appropriate one. This is consistent with previous work showing that protein deprivation increases exploratory behavior in individual caterpillars and suggests that food quality can influence collective foraging in ways more complex than a simple distinction between high and low quality sources. Furthermore, the latency to initiate exploration also decreases with increasing group size, as the probability that a single individual initiates exploration increases. Contrary to previously studied species, amplification is not modulated according to source quality in this species; instead it is through effects on exploration that food protein content and caterpillar group size influence collective decision-making.

Impact of grazing management on hibernating caterpillars of the butterfly Melitaea cinxia in calcareous grasslands

Semi-natural grasslands are increasingly grazed by large herbivores for nature conservation purposes. For many insects such grazing is essential for the conservation of their habitat, but at the same time, populations decrease at high grazing intensity. We hypothesised that grazing management may cause increased butterfly mortality, especially for life-stages with low mobility, such as hibernating caterpillars. To test this, we measured the effect of sheep grazing on overwinter larval survival. We used the Glanville fritillary (Melitaea cinxia), which has gregarious caterpillars hibernating in silk nests, as a model species. Caterpillar nests were monitored throughout the hibernating period in calcareous grassland reserves with low and high intensity sheep grazing and in an ungrazed control treatment. After grazing, 64 % of the nests at the high intensity grazing treatment were damaged or missing, compared to 8 and 12 % at the ungrazed and low intensity grazing treatment, respectively. Nest volume and caterpillar survival were 50 % lower at the high intensity grazing treatment compared to both ungrazed and low intensity grazing treatments. Nest damage and increased mortality were mainly caused by incidental ingestion of the caterpillars by the sheep. It is likely that grazing similarly affects other invertebrates, depending on their location within the vegetation and their ability to actively avoid herbivores. This implies that the impact of grazing strongly depends on the timing of this management in relation to the phenology of the species. A greater focus on immature and inactive life-stages in conservation policy in general and particularly in action plans for endangered species is required to effectively preserve invertebrate diversity.

Survival patterns under Costa Rican field conditions of the gregarious caterpillar Euselasia chrysippe (Lepidoptera: Riodinidae), a potential biological control agent of Miconia calvescens (Melastomataceae) in Hawaii

Survival of Euselasia chrysippe, a natural herbivore of Miconia calvescens, was investigated under field and laboratory conditions in Costa Rica as part of a biological control program in Hawaii. Following its introduction to Pacific islands, M. calvescens has become a dominant invasive species and the gregarious caterpillar of E. chrysippe has emerged as a promising biological control candidate. Under laboratory conditions, survivorship from egg to adult was 63%. E. chrysippe produced viable clutches in an experimental field plot. Similar clutch sizes occurred in both natural habitats and the experimental plot. Stage-specific life tables encompassing two years in the experimental plot indicate that larval survivorship from egg to the end of the sixth instar was about 10%. Egg parasitism was low in natural habitats and nil under experimental conditions. Larval group sizes were similar in natural and experimental field conditions, suggesting that survivorship is similar in both environments. During the coldest dry period no larvae survived past the fifth instar. Rainfall was a limiting factor for the survivorship of E. chrysippe in the experimental plot, but temperature appears to be the factor that would limit the effect of E. chrysippe on M. calvescens in Hawaii. Efforts should be invested in natural quarantine facilities to provide a testing ground for this species in target environments.

Temperature, size, reproductive allocation, and life-history evolution in a gregarious caterpillar

The present study aimed to investigate the relationship between growth rate, final mass, and larval development, as well as how this relationship influences reproductive trade-offs, in the context of a gregarious life-style and the need to keep an optimal group size. We use as a model two sympatric populations of the pine processionary moth Thaumetopoea pityocampa, which occur in different seasons and thus experience different climatic conditions. Thaumetopoea pityocampa is a strictly gregarious caterpillar throughout the larval period, which occurs during winter in countries all over the Mediterranean Basin. However, in 1997, a population in which larval development occurs during the summer was discovered in Portugal, namely the summer population (SP), as opposed to the normal winter population (WP), which coexists in the same forest feeding on the same host during the winter. Both populations were monitored over 3 years, with an assessment of the length of the larval period and its relationship with different climatic variables, final mass and adult size, egg size and number, colony size, and mortality at different life stages. The SP larval period was reduced as a result of development in the warmer part of the year, although it reached the same final mass and adult size as the WP. Despite an equal size at maturity, a trade-off between egg size and number was found between the two populations: SP produced less but bigger eggs than WP. This contrasts with the findings obtained in other Lepidoptera species, where development in colder environments leads to larger eggs at the expense of fecundity, but corroborates the trend found at a macro-geographical scale for T. pityocampa, with females from northern latitudes and a colder environment producing more (and smaller) eggs. The results demonstrate the importance of the number of eggs in cold environments as a result of an advantage of large colonies when gregarious caterpillars develop in such environments, and these findings are discussed in accordance with the major theories regarding size in animals. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 340349.

Latitudinal gradients and the shaping of life-history traits in a gregarious caterpillar

The present study aimed to investigate how the impact of several factors linked to geography would shape life-history traits in a gregarious species, using the pine processionary moth (PPM) Thaumetopoea pityocampa as a model system. PPM has a wide geographical distribution over the Mediterranean Basin, and it is a strictly gregarious species throughout larval development, where the total reproductive output of each female forms a colony. We reviewed both published and unpublished data on PPM from all over its distribution in the Mediterranean Basin and extracted data on fecundity, egg size, egg parasitoid mortality, flight period, and development time. These life-history traits were then related to location, expressed as latitude and altitude, local average temperatures, and host tree species. We found that PPM fecundity increaseed with latitude, concomitant with an increase in the length of development and an earlier onset of adult flight. These results are the opposite of that found in other Lepidoptera species with a wide geographical distribution, as well as in insects in general. We propose that a large colony size in PPM is important at higher latitudes because this confers an advantage for thermoregulation and tent building in areas where larvae have to face harsher conditions during the winter, thus shifting the optimal trade-off between the number and size of eggs with latitude. However, host tree species also affected the relationship between egg number and size and the optimal outcome of these traits is likely a compromise between different selection pressures. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 224-236.

Group size effects on survivorship and adult development in the gregarious larvae of Euselasia chrysippe (Lepidoptera, Riodinidae)

Caterpillars living in aggregations may derive several benefits that outweigh the costs, including better survivorship and improved growth rates. I tested whether larval group size had an effect on these two vital rates in Euselasia chrysippe. These caterpillars feed gregariously during all instars and move in processionary form over the host plant and even pupate together. There was a positive relationship between group size and larval survivorship in the field, although genetic variability was not taken into account in this experiment. Under laboratory conditions, there was also a positive relationship between group size, and larval growth rate and adult weight. This supports the hypothesis that aggregations facilitate feeding and larval growth. Single sixth instar larvae in the laboratory also had a lower survivorship than larvae in groups. These results provide further evidence of the benefits of group living for gregarious caterpillars.

Physiological and biochemical distinctions between solitary and gregarious caterpillars of the meadow moth Loxostege sticticalis L. (Lepidoptera: Pyralidae)

ISSN 0012-4966, Doklady Biological Sciences, 2008, Vol. 422, pp. 316–317. © Pleiades Publishing, Ltd., 2008.Original Russian Text © A.A. Alekseev, V.V. Serebrov, O.N. Gerber, I.M. Dubovskii, V.V. Glupov, M.A. Ushakova, I.Yu. Rauschenba ch, 2008, published in Doklady Akademii Nauk,2008, Vol. 422, No. 2, pp. 270–272.

Pros and cons of group living in the forest tent caterpillar: separating the roles of silk and of grouping

AbstractGroup living can incur both benefits and costs, mediated by different mechanisms. In many gregarious caterpillars, collective use of a network of silk trails is thought to improve foraging. Grouping, i.e., close contact with conspecifics, has been postulated to have both positive (thermoregulation and predator defense) and negative (competition and pathogen transmission) effects. The present experiment distinguishes between silk produced by group members and grouping per se in their effects on growth and development of both early and late larval stadia of the forest tent caterpillar [Malacosoma disstriaHübner (Lepidoptera: Lasiocampidae)] in a laboratory context. For both developmental stadia tested, pre‐established silk trails decreased latency to food finding and hence increased food consumption and growth rate. For younger larvae, pre‐established silk also decreased investment in silk production. Grouping young caterpillars accelerated development at the expense of growth, possibly as a mechanism to avoid intraspecific competition in later larval stadia. In older caterpillars, grouping decreased meal duration, suggesting that competition can indeed occur towards the end of larval development, even in the presence of surplus food. This led to a decrease in growth without any effect on instar duration. The benefits of exogenous silk thus decreased during larval development, whereas the costs associated with crowding increased. Ontogenetic shifts in grouping are common in many taxa: the present study is among the first to provide empirical evidence for an adaptive explanation of observed ontogenetic changes in aggregative behavior.

Isolation and characterization of microsatellite markers from the panic moth, Saucrobotys futilalis L. (Lepidoptera: Pyralidae: Pyraustinae)

AbstractThe panic moth is a widely distributed North American pyralid moth with gregarious, nest‐building larvae. Primers for 12 polymorphic microsatellite loci were developed to assay relatedness in nest groups and population structure in the eastern half of the moth's range. Primers were tested on 42 individuals (one from each of 42 nests) collected in the states of New York, Virginia and Georgia. All loci were polymorphic and exhibited varying degrees of allelic variation (4–24 alleles). These primers will enable further research into the social structure of these gregarious caterpillars.

Ontogenetic changes in social behaviour in the forest tent caterpillar, Malacosoma disstria

Many animals, including gregarious caterpillars, begin life in groups and become increasingly solitary as they grow larger. These ontogenetic changes in social behaviour suggest that the costs and benefits of grouping change with increasing individual size. Forest tent caterpillar (Malacosoma disstria) colonies exhibit complex social behaviour during the early larval instars, using pheromone trails to move together between temporary bivouacs and feeding sites, and break up as the caterpillars grow. We demonstrate changes in individual responses to cues from conspecifics that explain changes in aggregation during caterpillar development. We used Markov chain analysis to test the influence of pheromone trails and colony-mates on an individual caterpillar’s tendency to switch between quiescence, searching, walking and spinning. Pheromone-laden silk trails increased the tendency to begin locomotion, whereas colony-mates increased switching from activity to quiescence. Trails also influenced the form taken by locomotor behaviour, and promoted directed walking over searching. Social cues thus increase the efficiency of individual locomotion. Younger larvae were more quiescent and more reluctant to walk in the absence of trails than were older insects. An increase in independent locomotion as the larvae grow provides a mechanism to explain colony break-up and points to an ontogenetic shift in the internal processes driving behaviour. Scaling relationships suggest that many of the benefits associated with group-living in caterpillars decrease as individuals grow larger, providing an adaptive explanation for observed ontogenetic changes in social behaviour.

Variation in Food Quality and Temperature Constrain Foraging of Gregarious Caterpillars

We examined the separate and combined effects of changing food quality, thermal environment, and larval behavior on the foraging pattern of a gregarious caterpillar. Hemileuca lucina (Saturniidae), which specializes on the shrub Spiraea latifolia (Rosaceae). First—instar larvae, which encounter only new leaves under field conditions, showed no preference for new leaves over mature ones. In contrast, third—instar larvae, which normally encounter both leaf types, exhibited a preference for new leaves, in both 12—h and instar length choice tests. In laboratory tests, larvae in groups were more likely to survive and exhibited less variation in biomass gained than solitary larvae. An experiment was conducted to determine the interactions of temperature (with daytime temperatures of 20°, 25°, or 30°C), group size (solitary or in groups of 10), and diet (new or mature leaves) on third—instar larvae. The effect of diet and group size on relative growth rate depended on the daytime temperature. At a daytime temperature of 20°, representing overcast and cool spring conditions, growth rates were similar for all group size—diet combinations. Thus, at such a cool temperature, there was no advantage in feeding on new leaves or in larval groups. In contrast, solitary larvae fed mature leaves gained less mass and developed more slowly than the other group size—diet combinations at the mean maximal day temperature (25°) for field conditions. At 30° representing the average temperature reached through basking, larvae eating new leaves grew significantly faster than those on mature leaves, regardless of larval group size. These results indicate that in the absence of predators, in which case larvae eat new leaves, bask, and remain aggregated, the larvae can grow twice as fast and attain more biomass per instar than solitary larvae eating mature leaves in the shade, which is often the case when they avoid predators.

Daily foraging schedule of field colonies of the eastern tent caterpillar Malacosoma americanum.

The daily foraging patterns of seven colonies of the eastern tent caterpillar, Malacosoma americanum, were monitored photoelectronically during the last three larval stadia to provide the first detailed record of the foraging behavior of a gregarious caterpillar under field conditions. Colonies were active an average of 49.3% of each day. Three bouts of foraging, centered about 0600 h, 1500 h and 2000 h (EST), occurred daily during the fourth and fifth stadia. Although ambient temperatures were less favorable for foraging and food processing than at other times of the day, the caterpillars were most active at dusk and dawn, and spent comparatively little time away from the tent during the daylight hours. In the last (sixth) stadium, the caterpillars foraged only under the cover of darkness. A lack of relationship between the rate at which the caterpillars processed food and the spacing of their feeding bouts, indicates that this species follows a schedule of feeding and growth shaped by factors other than those directly related to feeding efficiency and ambient temperature. Colony foraging patterns may reduce caterpillar mortality by minimizing contact between larvae and day-active predators and parasitiods.

Chemical trail marking and following by caterpillars ofMalacosoma neustria

Chemical trail marking and following by gregarious caterpillars,Malacosoma neustria L. (Lepidoptera: Lasiocampidae), was studied in the laboratory. As in other species ofMalacosoma, larvae deposit a trail pheromone from a sternal secretory site when searching the host for food. Larvae in the vanguard of foraging columns establish chemical trails as they explore new territory. Marking behavior diminishes as successive unfed foragers utilize the trail. These exploratory trails are subsequently overmarked by fed larvae returning to the tent. Other foragers follow the trails of fed larvae in preference to trails of unfed larvae. Thus, like the eastern tent caterpillar,M. americanum, successful foragers ofM. neustria recruit colony-mates to feeding sites. The chemical activity of both recruitment and exploratory trails degrades slowly, suggesting that the trail pheromone ofM. neustria is a nonvolatile substance. Caterpillars ofM. neustria readily follow the nonvolatile trail pheromone which has been identified fromM. americanum, 5β-cholestane-3,24-dione.