Communal Foraging Behavior and Recruitment Communication in Gloveria sp.

The caterpillars of Gloveria sp. mark trails with a pheromone they deposit by dragging the ventral surface of the tip of the abdomen along branch pathways as they move between their communal nest and distance feeding sites. The threshold sensitivity of the caterpillar for an extract prepared from the secretory site was approximately 0.5 × 10^–3 caterpillar equivalents/cm of trail. Bioassays show that Gloveria follows neither authentic trails of Malacosoma americanum nor artificial trails prepared from 5-cholestane-3-one, a chemical previously reported to elicit trail following from other social caterpillars. Although our observations show that fed caterpillars mark heavily as they return to their nest, we found no evidence that individual caterpillars are able to recruit hungry nestmates to new food finds. In this species, recruitment to food occurs only after many caterpillars have reinforced a trail to a newly discovered food source. In contrast, hungry caterpillars of the confamilial species M. americanum, tested under identical conditions, responded strongly to the postprandial trails of individual caterpillars and rapidly abandoned depleted sites in favor of new food finds. We postulate that the difference in the efficiency with which these two species recruit nestmates to food evolved in response to differences in the spatial distribution of their food supplies.     

A chemical trail factor from the silk of the eastern tent caterpillarMalacosoma americanum (Lepidoptera: Lasiocampidae)

The leaf-feeding larvae of the eastern tent caterpillarMalacosoma americanum (Fabricius) follow silk trails laid down on branches leading from their communal tent to distant foraging sites. The response of colonies reared in the laboratory under seminatural conditions to silk trails washed in methylene chloride and to chemical trails prepared from a solvent extract of their tent or trail silk, showed that one or more soluble components of their trail is essential to the elicitation of the following response. The demonstrated ability of the caterpillars to distinguish between old and newly reinforced silk trails most likely occurs in response to a temporal change in the detectable chemical properties of their trail.     

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, 5-cholestane-3,24-dione.     

Identification of trail pheromone of larva of eastern tent caterpillarMalacosoma americanum (Lepidoptera: Lasiocampidae)

Previous studies have shown that larvae of the eastern tent caterpillar (Malacosoma americanum F.) mark trails, leading from their tent to feeding sites on host trees, with a pheromone secreted from the posterior tip of the abdominal sternum. 5-Cholestane-3,24-dione (1) has been identified as an active component of the trail. The larvae have a threshold sensitivity to the pheromone of 10^–11 g/mm of trail. Several related compounds elicit the trail-following response. Two other species of tent caterpillars also responded positively to the pheromone in preliminary laboratory tests.     

Chemoorientation of eastern tent caterpillars to trail pheromone, 5β-Cholestane-3,24-dione

Chemoorientation behavior of the larval eastern tent caterpillar,Malacosoma americanum, was studied using the synthetic trail pheromone 5-cholestane-3,24-dione. Divergent arms of Y mazes were treated with various concentration ratios of the pheromone. At application rates of 10^–10-10^–9 g/mm of trail, larvae showed a significant preference for stronger trails when concentration ratios differed by as little as 4:1. At application rates of 10^–8 and greater there was no significant difference in trail choice even when trails differed in strength by a full order of magnitude. Other studies showed that the caterpillars abandon the pattern of choosing stronger over weaker trails when they repeatedly fail to find food at the end of a stronger trail. Experiments in which larvae were required to choose trails separated by a gap demonstrated orientation by chemoklinotaxis. Caterpillars that had one of the maxillary palps ablated looped in the direction of their intact chemo-receptor when placed on filter paper treated uniformly with pheromone, indicating that they may also orient by tropotaxis. The relevance of these findings to the tent caterpillar communication system is discussed.     

Trail and arena marking by caterpillars ofArchips cerasivoranus (lepidoptera: Tortricidae)

The activity ofArchips cerasivoranus caterpillars is largely limited to their colonial silk web and trails. Silk pulled directly from the spinnerets of caterpillars and wound onto paper strips to form artificial trails elicited locomotion from the larvae. Trails made from extracts of silk and silk glands also elicited locomotion. These and other observations reported here indicate that the caterpillars are responsive to a water-soluble pheromone that is a component of the silk strand. Marker pheromones appear not to be secreted from other regions of the body, as has been reported for some other trail-following caterpillars.     

Specificity of trail markers of forest and eastern tent caterpillars

Exploratory trails deposited on paper strips by the forest tent caterpillar (FTC),Malacosoma disstria Hubner, and the eastern tent caterpillar (ETC),M. americanum (Fabricius), as well as extracts of these trails, readily elicited interspecific trail-following behavior. In 2-choice tests involving simple Y mazes constructed from these paper strips, the caterpillars of both species preferred by approximately 31 the trails of the FTC. Studies involving whole colonies of the ETC maintained under nearnatural conditions in the laboratory, however, indicated that the trails deposited by successful foragers of the ETC as they returned to their tent from feeding sites were more attractive than the exploratory trails of either the ETC or FTC. The pronounced interspecific response of these congeners to each other's trails suggests that they utilize either qualitatively similar or identical trail-marking chemicals. Both species preferred their own trails to those ofArchips cerasivoranus (Fitch) (Tortricidae), providing the first evidence that more distantly related lepidopterous larvae utilize distinct trails.     

Trail following and recruitment: Response of eastern tent caterpillarMalacosoma americanum to 5β-cholestane-3,24-dione and 5β-cholestan-3-one

Studies were conducted to determine the relative effectiveness of 5-cholestane-3,24-dione (diketone) and 5-cholestan-3-one (monoketone) in eliciting trail following from eastern tent caterpillars,Malacosoma americanum. In Y maze tests, trails prepared from the monoketone were followed preferentially over diketone trails, even when the diketone trail was several orders of magnitude stronger. Under field conditions, colonies readily abandoned well-developed trail systems in favor of artificial trails that were established with the monoketone. Other tests in which the caterpillars selected trails prepared from the monoketone (but not the diketone) more often than their own recruitment trails indicate that the monoketone constitutes the chemical basis of recruitment communication in this insect. The study also shows that tent caterpillars are highly sensitive to small differences in the amount of monoketone in a trail and can distinguish between new and aged trails prepared from the compound.     

Hexyl Decanoate, the First Trail Pheromone Compound Identified in a Stingless Bee, Trigona recursa

Foragers of many species of stingless bees guide their nestmates to food sources by means of scent trails deposited on solid substrates between the food and the nest. The corresponding trail pheromones are generally believed to be produced in the mandibular glands, although definitive experimental proof has never been provided. We tested the trail following behavior of recruits of Trigona recursa in field experiments with artificial scent trails branching off from natural scent trails of this stingless bee. First-time recruits (newcomers) did not follow these trails when they were laid with pure solvent or mandibular gland extract. However, they did follow trails made with labial gland extract. Chemical analyses of labial gland secretions revealed that hexyl decanoate was the dominant component (72.4 ± 1.9% of all volatiles). Newcomers were significantly attracted to artificial trails made with synthetic hexyl decanoate, demonstrating its key function in eliciting scent-following behavior. According to our experiments with T. recursa, the trail pheromone is produced in the labial glands and not in the mandibular glands. Hexyl decanoate is the first component of a trail pheromone identified and proved to be behaviorally active in stingless bees.     

Site of secretion of the trail marker of the eastern tent caterpillar

A new site of secretion of a chemical trail marker was found on the sternum at the tip of the last abdominal segment of the larva of the eastern tent caterpillarMalacosoma americanum. Larvae marked from this site by drawing their sterna along the substrate when they extended existing trails in search of food and again when they established recruitment trails to food-finds. Differences in the quantity or quality of the marker deposited by exploring and recruiting caterpillars may account for the greater activity of the recruitment trails.     

Aposematism in Archips cerasivoranus Not Linked to the Sequestration of Host-derived Cyanide

This study addressed the question of how caterpillars of Archips cerasivoranus feeding upon Prunus virginiana cope with the cyanogenic compounds of their food. Analysis by ion chromatography showed that young and aged leaves of P. virginiana consumed by the caterpillars during spring have hydrogen cyanide potentials (HCN-ps) of 2,473 +/- 130 ppm and 1,058 +/- 98 ppm, respectively. Although less than 3% of the cyanide released as the caterpillars feed escapes into the atmosphere, the larva's bright-yellow aposematic coloration and conspicuous activity can not be attributed to the sequestration of cyanide. Only six of 25 samples of the caterpillars' defensive regurgitants collected from 12 field colonies contained cyanide (17.6 +/- 6.54 ppm), less than 5% of the quantity previously reported to occur in the regurgitant of the tent caterpillar M. americanum. Only seven of 13 caterpillars assayed had detectable quantities of cyanide in their bodies (3.9 +/- 0.9 ppm). The fecal pellets that encase the cocoon contained no cyanide, nor did the frass that litters the leaf shelters. The small quantities of cyanide that occur in the caterpillar compared to the HCN-p of ingested plant material appear attributable to paced bouts of feeding and the maintenance of a highly alkaline foregut that inhibits cyanogenesis.     

Trail-following behavior ofReticulitermes hesperus Banks (Isoptera: Rhinotermitidae)

The behavior ofReticulitermes hesperus Banks pseudergates (workers) was assessed on artificial trails containing different concentrations of sternal gland extract. On nongiadient trails, more pseudergates were recruited to trails of greater pheromone concentration, they traveled a greater distance without pausing, and their rate of locomotion increased over that observed on trails of lesser concentration (positive orthokinesis). Of the individuals pausing before completing trails of high concentration, fewer left the trails or reversed direction (negative klinokinesis) than on trails of lower concentration. Termites walking down concentration gradients failed to complete these trails to the low-concentration termini. At a point representing an average decrease of slightly more than 10-fold in the original concentration of pheromone, individuals reversed their direction of travel and returned to the high-concentration terminus. Termites walking up pheromone gradients proceeded to the high-concentration termini without reversing direction.R. hesperus pseudergates are thus able to orient along a gradient of trail pheromone by longitudinal klinotaxis.     

A trail pheromone from silk produced by larvae of the range caterpillarHemileuca oliviae (Lepidoptera: Saturniidae) and observations on aggregation behavior

Methylene chloride-extractable chemical(s) from range caterpillar larval silk facilitates trail-following and aggregation by early-instar larvae, but late-instar larvae are less responsive to the pheromone. Larval aggregation does not reduce water loss when larvae are exposed to low humidity, nor does aggregation prevent predation by the antFormica neoclara Emery. Grouped larvae gain weight and complete early stadia more rapidly as compared to solitary larvae. Aggregation may provide increased visibility to herbivores and increase the impact of urticating spines, thereby decreasing inadvertant predation.     

Specificity of laboratory trail following by the argentine ant,Iridomyrmex humilis (Mayr), to (Z)-9-hexadecenal,analogs, and gaster extract

In laboratory trail-following bioassays of Argentine ant workers,Iridomyrmex humilis (Mayr), the geometric isomer, (E)-9-hexadecenal, of the trail pheromone component (Z)-9-hexadecenal elicited insignificant trail following as did the potentially more stable formate analogs, (Z)-7-tetradecenyl formate, (E)-7-tetradecenyl formate, and tetradecyl formate. Further, in direct choice tests, workers showed no preference for gaster extract trails (0.002 ant equiv/cm) over trails of (Z)-9-hexadecenal (0.2 ng/cm). Moreover, a 10-fold increase in synthetic trail concentration to 2.0 ng/cm caused (Z)-9-hexadecenal trails to be significantly preferred over gaster extract trails by trail-following ants.     

Chemical marker from silk ofYponomeuta cagnagellus

Trail following in lepidopterous larvae is often attributed to chemical markers, but only a few clear-cut examples are found in the literature. In this paper evidence is presented for a chemical basis of the trail following behaviour ofYponomeuta cagnagellus. (Lepidoptera: Yponomeutidae) The marker is shown to be very persistent under laboratory conditions and is water soluble. Several possible secretory sites were investigated, and it is concluded that the marker is probably secreted together with the silk from the labial gland. Problems associated with the demonstration of trail markers in caterpillars are discussed.     

Substrate Temperature Constrains Recruitment and Trail Following Behavior in Ants

In many ant species, foragers use pheromones to communicate the location of resources to nestmates. Mass-recruiting species deposit long-lasting anonymous chemical trails, while group-recruiting species use temporary chemical trails. We studied how high temperature influenced the foraging behavior of a mass-recruiting species (Tapinoma nigerrimum) and a group-recruiting species (Aphaenogaster senilis) through pheromone decay. First, under controlled laboratory conditions, we examined the effect of temperature on the trail pheromone of both species. A substrate, simulating soil, marked with gaster extract was heated for 10 min. at 25°, 35°, 45°, or 55 °C and offered to workers in a choice test. Heating gaster extract reduced the trail following behavior of the mass-recruiters significantly more than that of the group-recruiters. Second, analyses of the chemicals present on the substrate indicated that most T. nigerrimum gaster secretions vanished at 25 °C, and only iridodials persisted up to 55 °C. By contrast, A. senilis secretions were less volatile and resisted better to elevated temperatures to some extent. However, at 55 °C, the only chemicals that persisted were nonadecene and nonadecane. Overall, our results suggest that the foraging behavior of the group-recruiting species A. senilis is less affected by pheromone evaporation than that of the mass-recruiting species T. nigerrimum. This group-recruiting species might, thus, be particularly adapted to environments with fluctuating temperatures.     

Pheromone Disruption of Argentine Ant Trail Integrity

Disruption of Argentine ant trail following and reduced ability to forage (measured by bait location success) was achieved after presentation of an oversupply of trail pheromone, (Z)-9-hexadecenal. Experiments tested single pheromone point sources and dispersion of a formulation in small field plots. Ant walking behavior was recorded and digitized by using video tracking, before and after presentation of trail pheromone. Ants showed changes in three parameters within seconds of treatment: (1) Ants on trails normally showed a unimodal frequency distribution of walking track angles, but this pattern disappeared after presentation of the trail pheromone; (2) ants showed initial high trail integrity on a range of untreated substrates from painted walls to wooden or concrete floors, but this was significantly reduced following presentation of a point source of pheromone; (3) the number of ants in the pheromone-treated area increased over time, as recruitment apparently exceeded departures. To test trail disruption in small outdoor plots, the trail pheromone was formulated with carnuba wax-coated quartz laboratory sand (1 g quartz sand/0.2 g wax/1 mg pheromone). The pheromone formulation, with a half-life of 30 h, was applied by rotary spreader at four rates (0, 2.5, 7.5, and 25 mg pheromone/m²) to 1- and 4-m² plots in Volcanoes National Park, Hawaii. Ant counts at bait cards in treated plots were significantly reduced compared to controls on the day of treatment, and there was a significant reduction in ant foraging for 2 days. These results show that trail pheromone disruption of Argentine ants is possible, but a much more durable formulation is needed before nest-level impacts can be expected. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Volatile Stimuli Related to Feeding Activity of Nonprey Caterpillars, Spodoptera exigua, Affect Olfactory Response of the Predatory Mite Phytoseiulus persimilis

The effect of volatiles related to feeding activity of nonprey caterpillars, Spodoptera exigua, on the olfactory response of the predatory mites Phytoseiulus persimilis was examined in a Y-tube olfactometer. At a low caterpillar density (20 caterpillars on 10 Lima bean leaves), the predators were significantly more attracted to volatiles from infested leaves on which the caterpillars and their products were present or from infested leaves from which the caterpillars and their products had been removed when compared to volatiles from uninfested leaves. The predators, however, significantly avoided odors from 20 caterpillars and their products (mainly feces) removed from bean leaves. In contrast, at a higher caterpillar density (100 caterpillars on 10 Lima bean leaves), the predators avoided volatiles from caterpillar-infested bean leaves. Volatiles from infested leaves from which the caterpillars and their products had been removed were not preferred over volatiles from uninfested leaves. Volatiles from feces collected from 100 caterpillars were strongly avoided by the predators, while the behavior of the predatory mites was not affected by volatiles from 100 caterpillars removed from a plant. The data show that carnivorous arthropods may avoid nonprofitable herbivores. This avoidance seems to result from an interference of volatiles from herbivore products with the attraction to herbivore-induced plant volatiles.     

Argentine Ant Trail Pheromone Disruption is Mediated by Trail Concentration

Argentine ant trail pheromone disruption, using continuous release of the trail pheromone compound (Z)-9-hexadecanal, reduces the incidence of trails and foraging rates of field populations. However, little is known about the concentrations of pheromone required for successful disruption. We hypothesized that higher pheromone quantities would be necessary to disrupt larger ant populations. To test this, we laid a 30-cm long base trail of (Z)-9-hexadecanal on a glass surface at low and high rates (1 and 100 pg/cm) (Trail 1), and laid a second, shorter trail (Trail 2, 10 cm long, located 1.5 cm upwind) near the middle of Trail 1 at six rates (1, 10, 100, 1,000, 10,000, and 100,000 pg/cm). We then recorded and digitized movements of individual ants following Trail 1, and derived a regression statistic, r ², as an index of trail integrity, and also recorded arrival success at the other end of the trail (30 cm) near a food supply. Disruption of trails required 100 fold more pheromone upwind, independent of base-trail concentration. This implies that in the field, trail disruption is likely to be less successful against high ant-trail densities (greater concentration of trail pheromone), and more successful against newly formed or weak trails, as could be expected along invasion fronts.     

Behavioral evidence for multicomponent trail pheromone in the termite,Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae)

Evidence is presented for a multicomponent trail pheromone in the eastern subterranean termiteReticulitermes flavipes (Kollar). Choice tests were used to compare strength and persistency of trails made by termites in glass tubes. Tubes connected to termite nests for 24 hr were marked by termites with an extremely long-lasting chemical that persisted for at least one year, and a highly volatile substance that decayed in 15 min. Individual termites varied the trail they deposited under different circumstances. When removed from the nest and placed in a clean tube, they deposited a highly volatile substance. They left stronger and more persistent trails when exploring clean tubes attached to the nest. When they discovered a new food source, they left trails that were more attractive and far more persistent than trails made by exploring or displaced termites. A food trail made by 15 workers was still effective after 24 hr, whereas a trail made by 50 displaced workers, walking one after another through a tube, lasted only 5 min.