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.     

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.     

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.     

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.     

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.     

Trail-Following Pheromones in Basal Termites, with Special Reference to Mastotermes darwiniensis

In the framework of an evolutionary study, trail pheromones have been studied in the most basal extant termite, Mastotermes darwiniensis (Mastotermitidae), and two other basal termites, the Termopsidae Porotermes adamsoni (Porotermitinae) and Stolotermes victoriensis (Stolotermitinae). Although workers of M. darwiniensis do not walk in single file while exploring a new environment under experimental conditions and are unable to follow artificial trails in ‘open field’ experiments, they do secrete a trail-following pheromone from their sternal glands. This unique behavior might reflect a primitive function of communication of the sternal gland. The major component of the pheromone appears to be the same in the three basal species: the norsesquiterpene alcohol (E)-2,6,10-trimethyl-5,9-undecadien-1-ol. This represents a new chemical category of trail-following pheromones for termites. The quantity of pheromone was estimated as 20 pg/individual in M. darwiniensis, 700 pg/individual in P. adamsoni, and 4 pg/individual in S. victoriensis. The activity threshold was 1 ng/cm in M. darwiniensis and 10 pg/cm in P. adamsoni. In M. darwiniensis, the trail pheromone was secreted by sternal gland 4 and to a lesser degree by sternal gland 3, sternal gland 5 being almost inactive. This study highlighted phylogenetic relationships between the Mastotermitidae and two subfamilies of the Termopsidae, the Porotermitinae and the Stolotermitinae. Furthermore, it indicated a heterogeneity within the Termopsidae, with Porotermitinae and Stolotermitinae on one hand, and Termopsinae on the other. Finally, Mastotermitidae and Termopsidae, with C14 trail pheromones, are clearly separated from the Kalotermitidae, Rhinotermitidae, and Termitidae that secrete C12 or C20 trail pheromones.     

The protective effect of antioxidants to a phototoxin-sensitive insect herbivore,Manduca sexta

Photo-activated plant secondary compounds have been shown to be toxic to many organisms including insects. Insect defenses include behavioral mechanisms such as light avoidance, as well as specific biochemical defenses such as antioxidants and antioxidant enzymes. These antioxidant defenses eliminate or quench the deleterious singlet oxygen and free radicals formed by these phototoxins. In this paper we examined the role of dietary antioxidants in protecting the phototoxin-sensitive insect herbivoreManduca sexta. Elevated dietary levels of the lipid-soluble antioxidants-carotene and vitamin E resulted in a concentration-dependent reduction in the mortality associated with treatment ofM. sexta larvae with the phototoxic thiophene-terthienyl. Elevated levels of dietary ascorbic acid had no effect, whereas reduced levels greatly increased the toxicity of-terthienyl. Tissue levels of antioxidants were shown to increase substantially in larvae fed antioxidant-supplemented diets. The results suggest that the ability to absorb and utilize plant-derived antioxidants could be an important defense against photo-activated plant secondary compounds and may have allowed some insects to exploit phototoxic plants.     

The major component of the trail pheromone of the leaf-cutting ant,Atta sexdens rubropilosa forel

The major component of the trail pheromone of the South American leaf-cutting ant,Atta sexdens rubropilosa Forel, is 3-ethyl-2,5-dimethylpyrazine (II). Methyl and ethyl phenylacetate and methyl 4-methylpyrrole-2-carboxylate (I), which is the major component of the trail pheromone ofA. texana (Buckley) andA. cephalotes (L.), were also identified and may be minor components. The pheromone is stored in the poison gland.Atta sexdens sexdens (L.) also responds strongly to the pyrazine, which in large amounts evokes a weak response fromA. texana, A. cephalotes, andAcromyrmex octospinosus (Reich). Foraging workers ofAtta sexdens rubropilosa did not preferentially pick up baits impregnated with the pyrazine. The pyrazine was puffed into the nests ofA. cephalotes, and a particular response called milling was noted.     

Trail-following responses of the Argentine ant,Iridomyrmex humilis (Mayr), to a synthetic trail pheromone component and analogs

Behavioral evidence indicates that (Z)-9-hexadecenal (Z9-16ALD) is a trail pheromone component ofIridomyrmex humilis, and that the true trail pheromone may be multicomponent. Trail-following responses ofI. humilis workers to several concentrations of syntheticZ9-16ALD, a constituent of the Pavan's gland, were found to be comparable to responses to gaster extract trails containing ca. 100 times lessZ9-16ALD. Of the five aldehyde analogs tested, only (Z)-7-hexadecenal (Z7-16ALD) elicited significant trail-following. However, following responses to severalZ9-16ALD-Z7-16ALD combinations were lower than responses toZ9-16ALD alone. Trails on filter paper of biologically relevant concentrations ofZ9-16ALD lose activity within 2 hr in the laboratory. The release rate ofZ9-16ALD measured from filter paper trails was 0.25 ± 0.10 pg/cm-sec. This was used to estimate the trail-following threshold for this compound of Argentine ant workers.     

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.     

Dietary influences on terpenoids sequestered by the biological control agent Oxyops vitiosa: effect of plant volatiles from different Melaleuca quinquenervia chemotypes and laboratory host species

The weevil Oxyops vitiosa is an Australian species imported to Florida, USA, for the biological control of the invasive species Melaleuca quinquenervia. The larvae of this species feed on the leaves of their host and produce a shiny orange secretion that covers their integument. Previous results indicated that a major component of this secretion, viridiflorol, is sequestered from the host plant and repels a generalist predator, the red imported fire ant, Solenopsis invicta. When the larvae fed on a different chemotype of M. quinquenervia, which lacked viridiflorol but was rich in a different sesquiterpene, (E)-nerolidol, similar protection occurred. Solvent washes of these larvae indicated that (E)-nerolidol was sequestered from M. quinquenervia leaves and repelled S. invicta workers when applied to dog food baits at physiological concentrations (17.5, 35.0, and 52.5 g/mg). Additionally, -caryophyllene also repelled S. invicta workers when applied to dog food baits at concentrations that approximated those in the O. vitiosa larval secretions (3.5 and 35 g/mg). When the O. vitiosa larvae were fed leaves from laboratory hosts (nonfield hosts), similar repellent activity was found. This activity was traced to several of the same compounds (e.g., 1,8-cineole, viridiflorol) found to be active in their field host M. quinquenervia. These weevil larvae are opportunistic, sequestering the primary terpenoids in their host leaves that confer antipredator activity.     

Oviposition-deterring pheromone ofRhagoletis pomonella

We found that after the parasitoidOpius lectus has arrived on a fruit infested by eggs or early-instar larvae of its tephritid hostRhagoletis pomonella, the following stimuli act to retain it and elicit antennal tapping and oviposition probes: unidentified fruit chemical components; characteristic fruit shape, size and color; andR. pomonella oviposition-deterring pheromone. This is the first demonstration of an oviposition-deterring pheromone in a phytophagous insect serving as a kairomone to one of its parasitoids.O. alloeus, a parasitoid of lateinstar larvae ofR. pomonella, was not influenced by the pheromone. Possible use of the pheromone for management ofO. lectus in a multifacetedR. pomonella suppression program is discussed.     

Following of conspecific and avoidance of predator chemical cues by pine snakes (Pituophis melanoleucus)

The ability of hatchling pine snakes (Pituophis melanoleucus) to follow or avoid the chemical trails of conspecifics and a king snake (Lampropeltis getulus) on paper substrates was investigated inY-maze experiments. Hatchlings entered the arm with the adult conspecific trail and avoided the arm containing the king snake trail at a frequency much greater than that due to chance. The data support the hypotheses that pine snakes follow the chemical trails of adult conspecifics and avoid the chemical trails of a predator.     

Response of The Lacewing Chrysopa cognata to Pheromones of its Aphid Prey

The lacewing Chrysopa cognata, one of the principal predators of aphids in Korea, was tested for responses to the aphid sex pheromone components (4aS,7S,7aR)-nepetalactone and (1R,4aS,7S,7aR)-nepetalactol and the aphid alarm pheromone (E)--farnesene. Electroantennogram responses were obtained to the sex pheromone components but not to (E)--farnesene. The sex pheromone components were attractive in a Y-tube olfactometer assay and in field trials with water traps, but no attraction was observed to (E)--farnesene.     

Role of secondary metabolites in feeding associations between a predatory nudibranch,two grazing nudibranchs,and a bryozoan

The carnivorous nudibranchRoboastra tigris preys preferentially upon two nudibranchs,Tambja abdere andT. eliora, that in turn feed upon the bryozoanSessibugula translucens. All four organisms contain tambjamines A–D (I–IV) that were shown to be fish feeding inhibitors. When attacked byRoboastra, T. abdere secretes a distasteful mucus containing a total of 3 mg of the tambjamines that sometimes causes theRoboastra to break off the attack. Under similar circumstancesT. eliora attempts to swim away; it presumably contains insufficient of the tambjamines to deterRoboastra. Roboastra follows the slime trail of nudibranchs using contact chemoreception and reverses direction when the trail is broken. The slime trail ofT. abdere contains low concentrations of the tambjamines. In Y-maze experiments,T. eliora was attracted towards seawater containingS. translucens and seawater containing 10^–10 M tambjamines A and B (11) but was repelled by seawater containing > 10^–8 M tambjamines A and B. At higher concentrations the mixture of tambjamines may be recognized as an alarm pheromone.     

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.     

Metabolism of 1,8-cineole in tea tree (Melaleuca alternifolia andM. linariifolia) by pyrgo beetle (Paropsisterna tigrina)

The frass of the pyrgo beetle (Paropsisterna tigrina) feeding on commercial plantations of the terpinen-4-ol chemical variety of the Australian tea tree.Melaleuca alternifolia, was found to contain a volatile oil almost identical to the essential oil of the ingested leaf. When beetles were fed leaf containing substantial quantities of 1,8-cineole, the predominant frass metabolite as determined by MS, IR,¹³C and¹H NMR, GC, and CoGC was (+)-2-hydroxycineole. Both male and female adults and larvae metabolizedMelaleuca oils in similar ways.     

Effect of ethanol and α-pinene on response of ambrosia beetle,Trypodendron lineatum,to lineatin-baited funnel and drainpipe traps

The response ofT. lineatum to ethanol and -pinene, when used with the pheromone lineatin, was tested for two trap types. Funnel traps, which are passive barrier traps, caught significantly more beetles than drainpipe traps, which require an active response by the beetle to enter the trap. However, the response ofT. lineatum to the semiochemical treatments did not significantly differ for the two trap types. Treatments that included -pinene with the pheromone, either with or without ethanol, caught significantly moreT. lineatin than those with the pheromone alone. When ethanol and or -pinene were added to the pheromone significantly more female beetles were trapped than with pheromone alone. Male-female ratios were significantly lower for both types of traps when ethanol was included in the bait than for lineatin alone or with -pinene. A higher percentage of male beetles entered the drainpipe traps than was captured with funnel traps.