Trail-Based Communication in Social Caterpillars of Eriogaster lanestris (Lepidoptera: Lasiocampidae)

Caterpillars of Eriogaster lanestris (Lepidoptera: Lasiocampidae) mark trails as they move between feeding sites and their communal tent. They prefer new trails over aged ones. Hungry caterpillars prefer trails marked by fed caterpillars returning to the tent. Thus successful foragers direct tentmates to profitable food finds, in a manner similar to that of Malacosoma americanum. E. lanestris readily follows trails prepared from 5-cholestane-3-one, a component of the trail marker of M. americanum, when applied at a rate of 10^–10 g/cm. In choice tests, they preferred more highly concentrated over weaker trails. New trails are always established in groups, and the velocity increases from early to late caterpillars traversing a new trail.     

Foraging behavior and growth of isolated larvae of a social caterpillar, Malacosoma americanum

In laboratory experiments, isolated eastern tent caterpillars, Malacosoma americanum (Fabricius) (Lepidoptera: Lasiocampidae), grew more slowly than their grouped siblings even though factors previously reported to give grouped caterpillars an advantage were eliminated from our experimental design. Analysis of time-lapse videorecordings of daily foraging bouts showed that, despite their slower growth, isolated individuals fed significantly more often than their grouped siblings. This finding is consistent with previous observations showing that the rate at which tent caterpillars assimilate food is largely independent of foraging frequency and suggests that increased metabolic costs associated with superfluous activity may cause isolated caterpillars to grow slower. More rapid growth of grouped caterpillars also appears attributable to the significantly longer periods of time solitary caterpillars spent inactive during episodes of molting. Our study shows that the distinctive temporal pattern of foraging characteristic of intact colonies of eastern tent caterpillars is a emergent property of the group.     

A temperature-dependent developmental model for a nucleopolyhedrosis virus of the velvetbean caterpillar,Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Developmental times and rates of nucleopolyhedrosis virus infection in third-instar velvetbean caterpillar, Anticarsia gemmatalis, larvae were studied in the laboratory at a variety of constant and variable temperatures. Developmental time was considered to be time from inoculation until death. Viral infection exhibited a temperature optimum of ca. 30°C and was inhibited at 10 and 40°C. Mean developmental time of the virus ranged from 18.1 days (15°C) to 5.5 days (30°C). Means and standard deviations of viral developmental rates (= development time^?1) were used as inputs into a previously derived absolute reaction rate model designed to generate a set of kinetic constants usable in predicting developmental times. Actual distributions of viral cohort developmental times were compared to distributions generated by the model. Reasonable agreement between predicted and actual distributions was found at three of four temperatures tested.     

Chromosome‐level genome assembly of an important pine defoliator,Dendrolimus punctatus (Lepidoptera; Lasiocampidae)

Dendrolimus spp. are important destructive pests of conifer forests, and Dendrolimus punctatus Walker (Lepidoptera; Lasiocampidae) is the most widely distributed Dendrolimus species. During periodic outbreaks, this species is said to make “fire without smoke” because large areas of pine forest can be quickly and heavily damaged. Yet, little is known about the molecular mechanisms that underlie the unique ecological characteristics of this forest insect. Here, we combined Pacific Biosciences (PacBio) RSII single‐molecule long reads and high‐throughput chromosome conformation capture (Hi‐C) genomics‐linked reads to produce a high‐quality, chromosome‐level reference genome for D. punctatus. The final assembly was 614 Mb with contig and scaffold N50 values of 1.39 and 22.15 Mb, respectively, and 96.96% of the contigs anchored onto 30 chromosomes. Based on the prediction, this genome contained 17,593 protein‐coding genes and 56.16% repetitive sequences. Phylogenetic analyses indicated that D. punctatus diverged from the common ancestor of Hyphantria cunea, Spodoptera litura and Thaumetopoea pityocampa ~ 108.91 million years ago. Many gene families that were expanded in the D. punctatus genome were significantly enriched for the xenobiotic biodegradation system, especially the cytochrome P450 gene family. This high‐quality, chromosome‐level reference genome will be a valuable resource for understanding mechanisms of D. punctatus outbreak and host resistance adaption. Because this is the first Lasiocampidae insect genome to be sequenced, it also will serve as a reference for further comparative genomics.     

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.     

Not looking where you are leaping: a novel method of oriented travel in the caterpillar Calindoea trifascialis (Moore) (Lepidoptera: Thyrididae)

The prepupation caterpillar of the Southeast Asian moth Calindoea trifascialis constructs a leaf shelter that jumps across the ground using a jumping method novel among the insects. We found that movement path direction was correlated to the direction opposite to the most intense light. Correlated random walk (CRW) analyses found net squared displacements higher than predicted by a CRW, and fractal dimension analysis indicated straighter paths at large spatial scales. Rearing experiments showed high mortality from predation on the ground, but higher mortality resulted from sun exposure. We interpret jumping path orientation as an efficient search strategy to find shade in a variable landscape, given limited perception, in the presence of overheating and desiccation risks.     

Foraging behaviour and ecology of the Cape pangolin (Manis temminckii) in north‐western Zimbabwe

An ethogram was developed for the foraging Cape pangolin in order to construct activity budgets. Behaviour was classified into seven categories and nine types of feeding sites were recorded. Activity budgets of animals foraging in different vegetation types are presented to illustrate the importance of vegetation on behaviour patterns and feeding site utilization. Availability of feeding sites may depend on the vegetation type with trees, shrubs and woody debris comprising most feeding sites. Seven prey species were recorded. One animal displayed strictly diurnal activity which suggests greater variability in activity patterns than previously thought.     

Susceptibility of the pine processionary caterpillar Thaumetopoea pityocampa (Lepidoptera: Thaumetopoeidae) toward δ-endotoxins of Bacillus thuringiensis under laboratory conditions

A series of natural crystal proteins from B. thuringiensis subsp. Alesti 12–25, caucasicus, galleriae 11–67, galleriae 6–96, kenyae, and shondungensis and spore‐crystal preparations from finitimus 11–66 and from a recombinant strain of B. thuringiensis subsp. kurstaki expressing Cry 1 Ga1 only, were assessed as a toxic agent for the pine processionary caterpillar, Thaumetopoea pityocampa. Some preparations had a thoroughly investigated composition and contained Cry1Aa, Cry1Ab2, Cry1Ab7, Cry1D, Cry1F, Cry 1 Ga1, Cry9Aa, Cry26 crystal proteins, whereas crystals of B. thuringiensis subsp. caucasicus, kenyae, and shondungensis harboured predominantly unidentified toxins distant from commonly used prototypes. Bioassays were based on the simultaneous assignment of each treatment to groups of 20 full sibling first‐instar larvae, obtained from broods of a population from North‐western Italy. The toxin was applied to pine needles by the leaf dipping method and the effect was registered in both feeding inhibition and mortality. B. thuringiensis subsp. caucasicus, kenyae, galleriae 6–96, alesti, and galleriae 11–67 gave the best results in terms of both feeding inhibition and larval mortality. Broods tested in B. thuringiensis bioassays showed a substantial variation in susceptibility to the toxins, suggesting the potential development of resistance in the population.     

The Role of Tactile and Chemical Stimuli in the Formation and Maintenance of the Processions of the Social Caterpillar Hylesia lineata (Lepidoptera: Saturniidae)

Colonies of the social caterpillar Hylesia lineata (Lepidoptera: Satumiidae) form long, single-file, head-to-tail processions as they move between their shelters and distant feeding sites. Although investigations of other processionary species have implicated a silk trail in the processionary process, silk plays little or no role in initiating or maintaining processions in H. lineata. Studies we report here implicate both tactile stimuli and a trail pheromone in the establishment and maintenance of processions. Processionaries elicit locomotion in the individual preceding them in line by brushing their heads against prominent sulci that project from the tips of their abdomens. Caterpillars mark their pathways with a pheromone deposited by brushing the ventral surfaces of their last abdominal segments against the substrate. The persistent pheromone is soluble in hexanes and appears to be secreted from glandular setae found on the proximal regions of the anal prolegs and the venter. In Y-choice tests, caterpillars selected newer trails over older trails and stronger trails over weaker trails. They did not distinguish between trials deposited by newly fed caterpillars and those deposited by starved caterpillars. Despite the unidirectional nature of processions, there is no indication that caterpillars can determine from the trail alone the direction in which the procession advanced. The significance of these findings to the foraging ecology of the caterpillars is discussed.     

Larval Sociality in Three Species of Central-place Foraging Lappet Moths (Lepidoptera: Lasiocampidae): A Comparative Survey

We studied three species of Lasiocampidae with social, tent-building caterpillars in Northern Bavaria, viz. Eriogaster lanestris, Eriogaster catax, and Malacosoma neustria. We used key life-history data (number of larval instars, sizes and weights of eggs, caterpillars, and moths, size of egg clutches) as well as behavioral data (activity patterns, tent-building behavior, trail following behavior) for a comparative study. Although larvae of all three species are active only in spring, show overlapping habitat requirements, and use the same major host-plant (Prunus spinosa) with only minor differences in phenology, they show markedly different life-history and behavioral strategies.E. catax lays comparatively few but large eggs while E. lanestris lays more but smaller eggs. M. neustria lays the smallest eggs but large clusters. E. lanestris caterpillars build a large tent with an accessible interior while those of E. catax build a small tent that is only used as a resting and molting platform. M. neustria shows a flexible behavior, may abandon the primary tent and build a new one several times. M. neustria colonies also subdivide and reunite regularly while Eriogaster colonies stay together until larvae become solitary. In E. lanestris all tentmates of a colony are highly synchronized while foraging or resting. Instead, in E. catax small subgroups leave the tent for foraging while at every time the majority rests on the tent. M. neustria caterpillars forage more or less individually and only synchronize by night. Results are discussed in relation to other species of the genera Eriogaster and Malacosoma and with regard to the evolution and diversification of caterpillar sociality.     

Trail Marking and Abandonment of Depleted Feeding Sites by the Caterpillars of <Emphasis Type="Italic">Eutachyptera psidii</Emphasis> (Lepidoptera: Lasiocampidae)

The caterpillars of Eutachytptera psidii (Lepidoptera: Lasiocampidae) mark trails between their nest and distant feeding sites with a trail pheromone secreted from the ventral surfaces of their last abdominal segments. The threshold sensitivity to artificial trails prepared from an hexane extract of the pheromone was 0.75 × 10⁻³ caterpillar-equivalents per cm of trail. In tests of trail-specificity involving four other social species, the caterpillars responded only to trails prepared from a pheromone extract of the closely related genus Gloveria. Tests were conducted to determine the efficiency with which colonies abandon exhausted feeding sites in favor of new food finds. On their first forays after their food sources were experimentally moved from established feeding sites to new sites, 67.5 ± 3.6% of all the evening’s activity occurred on pathways leading to the previously established sites. During their next two forays, 86.3 ± 3.7% and 92.1 ± 2.0% of all activity occurred on pathways leading to the new sites. Efficient abandonment of exhausted feeding sites is attributed to the persistence of the trail pheromone, differential marking of new and old pathways and to the caterpillar’s ability to discern trail strength and to choose stronger over weaker trails at choice points.     

Stimulation of sex pheromone production by PBAN-like substance in the pine caterpillar moth, Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

Sex pheromone production in the female pine caterpillar moth, Dendrolimus punctatus is controlled by a PBAN-like substance located in the head of female moth. Pheromone titer was significantly decreased by decapitation of female moth, and restored by injection of either Hez-PBAN or head extract prepared from male or female moth. Stimulation of pheromone production by head extract followed a dose-dependent pattern from 0.5 to at least 4 head equivalent. A gland in vitro assay was used to study the relationship between gland incubation time and pheromone production as well as calcium involvement in the stimulation of pheromone production by head extract. Maximum pheromone production was occurred at 60 min after pheromone gland was incubated with two equivalents of head extracts. In vitro experiments showed that the presence of calcium in the incubation medium was necessary for stimulation of pheromone production. The calcium ionophore, A 23187, alone stimulated pheromone production. The pheromone components (Z,E)-5,7-dodecadienol and its acetate and propionate were produced in these experiments but in addition to the aldehyde, (Z,E)-5,7-dodecadienal was also found. This indicates that females are capable of producing four oxygenated functional groups. The PBAN-like substance control of the pheromone biosynthetic pathway was investigated by monitoring the incorporation of the labeled precursor into both pheromone and pheromone intermediates.     

Foraging in tropical rain forests: The case of the penan of Sarawak,East Malaysia (Borneo)

Bailey et al. (1989) and Headland (1987) have recently proposed hypotheses stating that human foragers are unable to live in undisturbed tropical rain forests without some reliance on cultivated foods. The present discussion considers these hypotheses, as well as some of the evidence by which they have been tested. Four conceptual problems in the way these hypotheses have been formulated are identified: (1) assumptions about the relationship between key features of tropical forest ecosystems and human subsistence potential, (2) in-consistencies in the definition of pure foraging, (3) adherence to a dichotomy between foraging and agriculture, the result being that conscious and unconscious effects of exploitation on the demographic parameters of key resources is ignored, and (4) problems in defining the significance of ecotones. I consider the case of Penan hunter-gatherers of Borneo, a population which, by virtue of their reliance on the sago palm Eugeissona utilis, contradicts the conclusions of Bailey et al. and Headland. I consider salient aspects of Penan reliance on Eugeissona, and describe how Penan exploitation of this resource may positively effect its availability. This case is seen to provide a challenge to the hypotheses of Bailey et al. and Headland, not only in the extent to which it contradicts their conclusions but, more significantly, in what it reveals about the assumptions upon which their hypotheses are based. This points to the need for greater precision in the definition of future hypotheses about foraging in tropical forests.     

Epizootics and behavioral alteration in the arctiid caterpillar Chionarctia nivea (Lepidoptera: Arctiidae) caused by an entomopathogenic fungus, Entomophaga aulicae (Zygomycetes: Entomophthorales)

We observed epizootics and behavioral alteration in the arctiid caterpillar Chionarctia nivea after infection by an entomopathogenic fungus, Entomophaga aulicae, in April at a riverbank in Kyoto Prefecture, central Japan. The density of arctiid cadavers infected with E. aulicae was 1.31 individuals/m². The critically ill caterpillars crawled up the dead stems of grasses and herbs such as the common reed Phragmites communis and the Japanese mugwort Artemisia indica var. maximowiczii to die at and near the highest parts of the stems, while the healthy larvae usually wandered on the ground and fed on the leaves of small herbs. This behavioral difference could be caused by infection with E. aulicae to enhance dispersal of conidia by active discharge in Entomophthorales with the aid of wind and rainfall.     

Effect of pine foliage damage on the incidence of larval diapause in the pine caterpillar Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

The pine caterpillar Dendrolimus punctatus (Walker) with a larval facultative diapause is one of the most destructive insect pests of the pine tree Pinus massoniana in China. The larvae feeding on pine trees with different damage levels were studied to determine the induction of diapause under both laboratory and field conditions. Developmental duration of larvae before the third instar was the longest when fed with 75%–90% damaged needles, followed by 25%–40% damaged needles and intact pine needles, whereas mortalities did not differ among different treatments under the conditions of 25° and critical photoperiod 13.5:10.5 L:D. At 25°, no diapause was induced under 15:9 L:D, whereas 100% diapause occurred under 12:12 L:D regardless of the levels of needle damage. Incidences of larvae entering diapause when they were fed with intact, 25%–40% and 75%–90% damaged pine needles were 51.7%, 70.8% and 81% under 13.5:10.5 L:D, respectively. Similar results were obtained in the field experiment. Incidence of diapause was significantly different among the pine needle damage levels of pine trees when the photoperiod was close to the critical day length, indicating that the effect of host plants on diapause induction was dependent on the range of photoperiod. The content of amino acid and sugar decreased and tannin increased in pine needles after feeding by the pine caterpillars, suggesting that changed levels of nutrients in damaged needles or a particular substance emitted by damaged pine trees was perhaps involved in the diapause induction of the pine caterpillar.     

The effects of group size and host species on development and survivorship of a gregarious caterpillar Halisidota caryae (Lepidoptera: Arctiidae)

Abstract. 1. The effect on growth and survivorship of the number of Halisidota caryae (Harris) caterpillars in groups feeding on three taxonomically distinct hosts was examined experimentally in the field.
2. Caterpillars grew more rapidly and survived better in larger sized groups than in smaller sized groups.
3. Caterpilliars grew more rapidly and survived better on Carya ovata (Koch) than on Hamamelis virginiana (L) or Quercus velutina (Lam.).
4. There were equal numbers of invertebrate predators on groups of different sizes and thus larger groups had significantly fewer predators per caterpillar than did smaller groups.
5. Invertebrate predators accounted for at least a 10% daily decrease in survivorship.
6. Local movement reduced predation because moving groups had fewer predators than did stationary groups.     

Foraging behaviour of Brachionus calyciflorus (Pallas): variations in the swimming path according to presence or absence of algal food (Chlorella)

Both swimming and attachment behaviour of immature female Brachionus calyciflorus (Pallas) from a young orthoclone were analyzed under four experimental conditions: with and without algae (Chlorella), and with fed and starved individuals. Eighteen hours before the recording, two random groups were formed. To the first group, Chlorella was added. The second was placed in pure water. Both were filmed in red light to avoid a phototactic effect. Video-recorded swimming behaviour of B. calyciflorus was analyzed by automatic tracking. Each B. calyciflorus was filmed alternately in the presence or absence of Chlorella for five periods of 15 min. Under indentical light and temperature conditions the number of animals attached to the culture dish was measured with both starved and fed females. We observed a significant difference in swimming paths depending on the presence or absence of food, and the physiological state of the individuals. In the presence of Chlorella the linear speed was lower and the angular speed was greater. This increase in angular speed was more pronounced when females were subjected to a period of starvation before the experimentation. The attachment behaviour increased in the algal environment. This modification of swimming behaviour enables females to increase the time spent in a favorable food environment.