The Chafer Pheromone Buibuilactone and Ant Pyrazines are also Produced by Marine Bacteria

Headspace extracts obtained from agar plate cultures of two marine bacteria from the North Sea (Germany), Loktanella strain BIO-204 and Dinoroseobacter shibae strain DFL-27, were analyzed by GC-MS. Several -lactones and one -lactone were identified, besides pyrazines and some sulfur compounds. The absolute configuration of the major lactone (R,Z)-dodec-5-en-4-olide, known as buibuilactone, a pheromone of several scarab beetles, was determined by a new catalytic enantioselective synthesis and GC on a chiral stationary phase. Unsaturated lactones in the extracts included (E)-dodec-5-en-4-olide and the regioisomer (Z)-dodec-6-en-4-olide, previously identified as a component of black-tailed deer urine. The pyrazines 2-butyl-3,6-dimethylpyrazine and 2-isopentyl-3,6-dimethylpyrazine were identified by comparison with synthesized material. The latter compound is a known ant pheromone, as is another identified pyrazine, 2-ethyl-3,6-dimethylpyrazine. The striking similarity between insect pheromones and these bacterial volatiles is discussed, suggesting the possibility of more widespread occurrence of symbiosis between microorganisms and insects than previously thought.     

Solitary Foraging in the Ancestral South American Ant, <Emphasis Type="Italic">Pogonomyrmex vermiculatus</Emphasis>. Is it Due to Constraints in the Production or Perception of Trail Pheromones?

Several North American species of Pogonomyrmex harvester ants exhibit group foraging, whereas South American species are exclusively solitary foragers. The composition of the secretions of the poison and Dufour glands in the South American species, Pogonomyrmex vermiculatus, were analyzed, and the secretions and their components were tested as trail pheromones in laboratory bioassays. The major compounds in the poison gland were the alkylpyrazines, 2,5-dimethylpyrazine, 2,3,5-trimethylpyrazine, and 3-ethyl-2,5-dimethylpyrazine. The Dufour gland contained five alkanes, from tridecane to heptadecane, with pentadecane being most abundant. In behavioral bioassays, poison gland extracts and the mixture of pyrazines produced a trail pheromone effect, whereas the Dufour gland extracts and the alkanes had no effect on ant locomotion. We conclude that group foraging in P. vermiculatus does not arise from the inability to produce or detect possible pheromones, but rather, from physiological and/or ecological factors.     

Trail Pheromone Disruption of Red Imported Fire Ant

The fire ant, Solenopsis invicta (Hymenoptera: Formicidae), is considered one of the most aggressive and invasive species in the world. Toxic bait systems are used widely for control, but they also affect non-target ant species and cannot be used in sensitive ecosystems such as organic farms and national parks. The fire ant uses recruitment pheromones to organize the retrieval of large food resources back to the colony, with Z,E-α-farnesene responsible for the orientation of workers along trails. We prepared Z,E-α-farnesene, (91% purity) from extracted E,E-α-farnesene and demonstrated disruption of worker trail orientation after presentation of an oversupply of this compound from filter paper point sources (30 μg). Trails were established between queen-right colony cells and food sources in plastic tubs. Trail-following behavior was recorded by overhead webcam, and ants were digitized before and after presentation of the treatment, using two software approaches. The linear regression statistic, r ² was calculated. Ants initially showed high linear trail integrity (r ² = 0.75). Within seconds of presentation of the Z,E-α-farnesene treatment, the trailing ants showed little or no further evidence of trail following behavior in the vicinity of the pheromone source. These results show that trailing fire ants become disorientated in the presence of large amounts of Z,E-α-farnesene. Disrupting fire ant recruitment to resources may have a negative effect on colony size or other effects yet to be determined. This phenomenon was demonstrated recently for the Argentine ant, where trails were disrupted for two weeks by using their formulated trail pheromone, Z-9-hexadecenal. Further research is needed to establish the long term effects and control potential for trail disruption in S. invicta.     

Semiochemicals released by electrically stimulated red imported fire ants,Solenopsis invicta

The red imported fire ant Solenopsis invicta Buren, has evolved sophisticated chemical communication systems that regulate the activities of the colony. Among these are recruitment pheromones that effectively attract and stimulate workers to follow a trail to food or alternative nesting sites. Alarm pheromones alert, activate, and attract workers to intruders or other disturbances. The attraction and accumulation of fire ant workers in electrical equipment may be explained by their release of pheromones that draw additional worker ants into the electrical contacts. We used chemical analysis and behavioral bioassays to investigate if semiochemicals were released by electrically shocked fire ants. Workers were subjected to a 120 V, alternating-current power source. In all cases, electrically stimulated workers released venom alkaloids as revealed by gas chromatography. We also demonstrated the release of alarm pheromones and recruitment pheromones that elicited attraction and orientation. Arrestant behavior was observed with the workers not electrically stimulated but near those that were, indicating release of unkown behavior-modifying substances from the electrically stimulated ants. It appears that fire ants respond to electrical stimulus by generally releasing exocrine gland products. The behaviors associated with these products support the hypothesis that the accumulation of fire ants in electrical equipment is the result of a foraging worker finding and closing electrical contacts, then releasing exocrine gland products that attract other workers to the site, who in turn are electrically stimulated.     

Biochemical and behavioral evidence foe hybridization between fire ants,Solenopsis invicta andSolenopsis richteri (Hymenoptera: Formicidae)

Behavioral and biochemical evidence is presented for hybridization between the fire ants,Solenopsis richteri andS. invicta. The response of the two species to extracts of their trail pheromones presented as a point source is clearly species-specific; however, hybrid workers responded to parental Dufour's gland extracts and parental workers responded to Dufour's gland extracts of the hybrid. The behavioral evidence for hybridization was confirmed by gas Chromatograph comparison of the Dufour's gland extracts of the three fire ant forms, which showed a pattern for the hybrid that was intermediate to the two parental species.     

Alarm Pheromone Composition and Behavioral Activity in Fungus-Growing Ants

Chemical communication is a dominant method of communication throughout the animal kingdom and can be especially important in group-living animals in which communicating threats, either from predation or other dangers, can have large impacts on group survival. Social insects, in particular, have evolved a number of pheromonal compounds specifically to signal alarm. There is predicted to be little selection for interspecific variation in alarm cues because individuals may benefit from recognizing interspecific as well as conspecific cues and, consequently, alarm cues are not normally thought to be used for species or nestmate recognition. Here, we examine the composition of the alarm pheromones of seven species of fungus-growing ants (Attini), including both basal and derived species and examine the behavioral responses to alarm pheromone of Acromyrmex leaf-cutting ants, the sister genus to the highly studied Atta leaf-cutting ants. We find surprisingly high interspecific variation in alarm pheromone composition across the attine phylogeny. Interestingly, the active component of the alarm pheromone was different between the two leaf-cutting ant genera. Furthermore, in contrast to previous studies on Atta, we found no differences among morphological castes in their responses to alarm pheromone in Acromyrmex but we did find differences in responses among putative age classes. The results suggest that the evolution of alarm communication and signaling within social insect clades can be unexpectedly complex and that further work is warranted to understand whether the evolution of different alarm pheromone compounds is adaptive.     

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.     

Mandibular gland allomones ofDasymutilla occidentalis and other mutillid wasps

The mandibular gland secretion of the mutillid wasp,Dasymutilla occidentalis, possesses three short-chained ketones-4-methyl-3-heptanone (4MH), 4,6-dimethyl-3-nonanone (4,6DMN), 4,6-dimethyl-3-octanone (4,6DMO)—and several unidentified compounds. This is the first report of 4,6DMN as a natural product and its synthesis is described. These ketones, which are either known to be ant alarm pheromones or are structurally very similar to ant alarm pheromones, appear to function as allomones against ants, major potential predators of mutillid wasps. The major secretory component, 4-methyl-3-heptanone, which was identified in females and/ or males of the species analyzed within the generaDasymutilla, Timulla, Traumatomutilla, andPappognatha, appears to constitute a chemical character of the defensive secretions of these genera.     

Trail Pheromone Disruption of Argentine Ant Trail Formation and Foraging

Trail pheromone disruption of invasive ants is a novel tactic that builds on the development of pheromone-based pest management in other insects. Argentine ant trail pheromone, (Z)-9-hexadecenal, was formulated as a micro-encapsulated sprayable particle and applied against Argentine ant populations in 400 m² field plots in Hawai‘i Volcanoes National Park. A widely dispersed point source strategy for trail pheromone disruption was used. Traffic rates of ants in bioassays of treated filter paper, protected from rainfall and sunlight, indicated the presence of behaviorally significant quantities of pheromone being released from the formulation for up to 59 days. The proportion of plots, under trade wind conditions (2–3 m s⁻¹), with visible trails was reduced for up to 14 days following treatment, and the number of foraging ants at randomly placed tuna-bait cards was similarly reduced. The success of these trail pheromone disruption trials in a natural ecosystem highlights the potential of this method for control of invasive ant species in this and other environments.     

Identification of trail pheromone of the antTetramorium caespitum L. (Hymenoptera: Myrmicinae)

The trail pheromone of the antTetramorium caespitum L. is a 7030 mixture of 2,5-dimethylpyrazine and 3-ethyl-2, 5-dimethylpyrazine. The average total amount of the two pyrazines present in the poison vesicle was found to be 3.9 ng per ant, of which 2.7 ± 0.4 ng is 2,5-dimethylpyrazine and 1.15 ±0.25 ng is 3-ethyl-2,5-dimethylpyrazine. The pyrazines constitute only 0.03% of the volume of the poison vesicle but account for the whole of the trail-following activity. A 7030 mixture of the respective pyrazines evoked the highest activity in artificial trail-following tests.     

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.     

Cross-reaction to skin extract between two gobies,Asterropteryx semipunctatus andBrachygobius sabanus

Two gobies that possess alarm pheromones were tested for cross-reactions to water extracts of injured members of the other species in the first such cross-reaction test conducted in the Family Gobiidae.A. semipunctatus reacted to extract from injuredBrachygobius sabanus with the same bobbing and reduction in activity as it shows in response to conspecific extract. However,B. sabanus showed a feeding response, including increased activity, to extract from injuredA. semipunctatus. Even a one-way cross-reaction suggests some degree of homology between the alarm pheromone systems of the two species.     

Major hydrocarbons of the post-pharyngeal glands of mated queens of the red imported fire antSolenopsis invicta

Thin layer and column chromatographic analyses showed that hydrocarbons were the major lipoidal components of post-pharyngeal glands of mated queens of the red imported fire ant,Solenopsis invicta. Gas liquid chromatographic analyses on an OV-17 column showed four major hydrocarbons which have been identified and confirmed by synthesis and comparative mass spectral analyses as 13-methylheptacosane, 13,15-dimethylheptacosane, 3-methylheptacosane, and 3,9-dimethylheptacosane. When microgram quantitites of the natural alkanes on filter paper were placed in colonies of ants, the ants clustered on the paper about the sample and proceeded to masticate the paper in the area containing the alkanes.     

Isolation of the trail recruitment pheromone ofSolenopsis invicta

TheSolenopsis invicta trail pheromone is synthesized by the Dufour's gland and is released through the sting apparatus. The recruitment subcategory of theS. invicta trail pheromone was shown to be composed of a mixture of the orientation pheromone, (Z,E)--farnesene and an unidentified homosesquiterpene consisting of three rings and one double bond (C-1). C-1 is present in worker Dufour's glands at only 75 pg per worker equivalent. This is the first report that demonstrates that different exocrine products from the same gland control different subcategories of behavior related to mass recruitment.     

Identification of Chemicals Emitted by Calling Males of the Sapote Fruit Fly, <Emphasis Type="Italic">Anastrepha serpentina</Emphasis>

Emissions from sexually active Anastrepha serpentina males were collected by solid-phase microextraction. Calling behavior of wild-type males showed no clear peak during the day, except that it was evident less frequently immediately after daybreak and just before dark. Calling by laboratory males was highest between 8 and 11 h after onset of the photophase, and mating by wild flies occurred mostly between 6 and 10 h after onset of the photophase. Two major components of male emissions were identified as 2,5-dimethylpyrazine (DMP) and 3,6-dihydro-2,5-dimethylpyrazine (DHDMP). DHDMP was synthesized, and the identity of the natural product confirmed by comparison of gas chromatographic retention times and mass spectrum. Emissions of DMP and DHMP were greatest during peak calling behavior, with males emitting up to 1.8 and 3.3 μg/h of DMP and DHDMP, respectively. A minor component, which did not vary with time of day, was identified as 2,3,5-trimethylpyrazine. To our knowledge, this is the first report of 3,6-dihydro-2,5-dimethylpyrazine in nature. D. C. Robacker and R. J. Bartelt are now retired.     

Queen Sex Pheromone of the Slave-making Ant, Polyergus breviceps

Workers of the slave-making ant, Polyergus breviceps, raid nests of Formica ants and return with Formica pupae that mature into worker ants in the slave-makers’ colony. These Formica workers then tend the Polyergus brood, workers, and reproductives. During raids in the mating season, winged virgin Polyergus queens accompany the workers in the raiding columns. During the raid, the virgin queens release a pheromone that attracts males that quickly mate with the queens. We report the identification, synthesis, and bioassay of the sex attractant pheromone of the queens as an approximately 1:6 ratio of (R)-3-ethyl-4-methylpentan-1-ol and methyl 6-methylsalicylate. The ants produce exclusively the (R)-enantiomer of the alcohol, and the (S)-enantiomer has no biological activity, neither inhibiting nor increasing attraction to blends of methyl 6-methylsalicylate with the (R)-enantiomer.     

Sex Attractant Pheromones of Virgin Queens of Sympatric Slave-Making Ant Species in the Genus <Emphasis Type="Italic">Polyergus,</Emphasis> and their Possible Roles in Reproductive Isolation

Species of the ant genus Polyergus are social parasites that steal brood from colonies of their hosts in the closely related genus Formica. Upon emergence as adults in a mixed population, host Formica workers carry out all the normal worker functions within the Polyergus colony, including foraging, feeding, grooming, and rearing brood of the parasitic Polyergus ants. Some unmated Polyergus gynes (queens) run in the raiding columns of their colonies and attract males by releasing a pheromone from their mandibular glands. There are two Polyergus species groups in North America: an eastern P. lucidus group and a western P. breviceps group. One species of each of these groups, P. lucidus Mayr and P. mexicanus Emery, are sympatric in Missouri. In this study, we characterized the sex pheromones of virgin queens of two species of the P. lucidus group (P. lucidus sensu stricto and P. sanwaldi) and one species of the P. breviceps group (P. mexicanus), and compared these with the previously identified sex pheromone of P. topoffi of the P. breviceps group. We then used sex pheromone blends reconstructed from synthesized components of the two groups to test their efficacy at reproductively isolating these species. We found that methyl 6-methylsalicylate is conserved as the major component of the pheromone blends for both Polyergus species groups; however, methyl (R)-3-ethyl-4-methylpentanoate is the species-specific minor component produced by P. lucidus group queens, and (R)-3-ethyl-4-methylpentan-1-ol is the crucial minor component for P. breviceps group queens. The optimal ratio of the major and minor components for P. lucidus group queens was about 100:1 salicylate to ester. In concurrent field trials in Missouri, males of P. lucidus sensu stricto and P. mexicanus (a member of the P. breviceps group) were attracted almost exclusively to their particular blends of sex pheromone components. To our knowledge, this is the first example of a possible sex-pheromone-based reproductive isolating mechanism in ants.     

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.     

Male-Produced Aggregation Pheromone of the Cerambycid Beetle <Emphasis Type="Italic">Rosalia funebris</Emphasis>

We report the identification, synthesis, and field bioassays of a volatile, male-produced aggregation pheromone of a long-horned beetle, the banded alder borer, Rosalia funebris Mots. Headspace collections from males contained a major male-specific compound, (Z)-3-decenyl (E)-2-hexenoate, and several minor components, identified as (Z)-3-decenol, (Z)-3-nonenyl (E)-2-hexenoate, and (Z)-3-decenyl (E)-3-hexenoate. The antennae of both males and females responded strongly to (Z)-3-decenyl (E)-2-hexenoate. We collected significant numbers of adult R. funebris in field bioassays using traps baited with this compound. This pheromone structure is unprecedented in the literature of cerambycid pheromones and distinct from the more common diol/hydroxyketone pheromone motif of many other species of the diverse subfamily Cerambycinae. This is the first pheromone identified for a species in the tribe Rosaliini. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interactions Between Host-plant Volatiles and the Sex Pheromones of the Bird Cherry-oat Aphid, <Emphasis Type="Italic">Rhopalosiphum padi</Emphasis> and the Damson-hop Aphid, <Emphasis Type="Italic">Phorodon humuli</Emphasis>

The bird cherry-oat aphid, Rhopalosiphum padi (L.), and the damson-hop aphid, Phorodon humuli (Schrank), migrate at the same time of year and colonize closely related Prunus spp. as primary hosts, but utilize (1R,4aS,7S,7aR)-nepetalactol and (1RS,4aR,7S,7aS)-nepetalactol, respectively, as sex pheromones. Interactions between these sex pheromones and benzaldehyde and methyl salicylate, plant volatiles common to primary hosts of both species, were investigated to assess whether they confer reproductive isolation between these species. Female autumn migrants (gynoparae) and males of these two species were caught in the field with water traps baited with their respective sex pheromones. Rhopalosiphum padi gynoparae and males also responded positively to benzaldehyde. Release of either benzaldehyde or methyl salicylate with the conspecific sex pheromone increased catches of both species of aphid. However, releasing both plant volatiles with the sex pheromone of R. padi increased catches of gynoparae and males, but reduced those with the sex pheromone of P. humuli. These results support the hypothesis that specific plant volatiles synergize responses of autumn migrating aphids to their sex pheromone. Because these interactions are species-specific, they may be important in allowing males to discriminate between conspecific sexual females (oviparae) and those of other aphid species.