2,3-Dimethyl-5-(2-methylpropyl)pyrazine, a trail pheromone component of Eutetramorium mocquerysi Emery (1899) (Hymenoptera: Formicidae)

 The ant Eutetramorium mocquerysi (Myrmicinae) is endemic to the island of Madagascar. During foraging and nest emigration the ants lay recruitment trails with secretions from the poison gland. We identified three pyrazine compounds in the poison gland secretion: 2,3-dimethyl-5-(2-methylpropyl)pyrazine 1, 2,3-dimethyl-5-(3-methylbutyl)pyrazine 3, 2,3-dimethyl-5-(2-methylbutyl)pyrazine 4. Only the first component elicited trail-following behavior in the ants. We were unable to investigate whether the other pyrazine components have a synergistic function. Received: 21 February 2000 / Accepted in revised form: 27 June 2000     

(3R,4S)-Methyl-3-heptanol,the trail pheromone of the ant Leptogenys diminuta

We wish to thank Prof. V. Schurig (Tübingen) for lending us the columns for preliminary studies, and Prof. K. Mori (Tokyo), N. Frighetto and R. T. S. Frighetto (Erlangen) for optically active samples of 4-methyl-3-heptanol. This work was supported by the Deutsche Forschungsgemeinschaft.     

Thelytokous parthenogenesis by queens in the dacetine ant Pyramica membranifera (Hymenoptera: Formicidae)

Thelytokous parthenogenesis in which diploid females are produced from unfertilized eggs, was recently reported for some ant species. Here, we document thelytokous reproduction by queens in the polygynous species Pyramica membranifera. Queens that emerged in the laboratory were kept with or without workers under laboratory conditions. Independent colony founding was successful for a few queens if prey was provided. All artificial colonies, which started with a newly emerged queen and workers produced new workers and some of the colonies also produced female sexuals. Some of the female sexuals shed their wings in the laboratory and started formation of new polygynous colonies. Workers had no ovaries and thus, were obligatorily sterile.     

Pheromone communication and the mushroom body of the ant, Camponotus obscuripes (Hymenoptera: Formicidae)

Communication by means of pheromones plays predominant roles in colony integration by social insects. However, almost nothing is known about pheromone processing in the brains of social insects. In this study, we successfully applied intracellular recording and staining techniques to anatomically and physiologically characterize brain neurons of the ant Camponotus obscuripes. We identified 42 protocerebral neurons that responded to undecane and/or formic acid, components of alarm pheromones that evoke attraction or evasive behavior, respectively. Notably, 30 (71%) of these neurons were efferent (output) or feedback neurons of the mushroom body, and many of these exhibited different responses to formic acid and undecane. Eight of the remaining 12 neurons had arborizations in the lateral and/or medial protocerebrum, which receive terminations of efferent neurons of the mushroom body and from which premotor descending neurons originate. The remaining four neurons were bilateral neurons that connect lateral accessory lobes or dorsal protocerebrums of both hemispheres. We suggest that the mushroom body of the ant participates in the processing of alarm pheromones. Seventeen (40%) of 42 neurons exhibited responses to nonpheromonal odors, indicating that the pheromonal and nonpheromonal signals are not fully segregated when they are processed in the protocerebrum. This may be related to modulatory functions of alarm pheromones, i.e., they change alertness of the ant and change responses to a variety of sensory stimuli.     

A contact sex pheromone component of the emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)

Analyses of the elytral hydrocarbons from male and female emerald ash borer, Agrilus planipennis Fairmaire, that were freshly emerged vs. sexually mature (>10 days old) revealed a female-specific compound, 9-methyl-pentacosane (9-Me-C₂₅), only present in sexually mature females. This material was synthesized by the Wittig reaction of 2-decanone with (n-hexadecyl)-triphenylphosphonium bromide followed by catalytic reduction to yield racemic 9-Me C₂₅, which matched the natural compound by gas chromatography/mass spectrometry (retention time and EI mass spectrum). In field bioassays with freeze-killed sexually mature A. planipennis females, feral males spent significantly more time in contact and attempting copulation with unwashed females than with females that had been washed in n-hexane to remove the cuticular lipids. Hexane-washed females to which 9-Me-C₂₅ had been reapplied elicited similar contact time and percentage of time attempting copulation as unwashed females, indicating that 9-methyl-pentacosane is a contact sex pheromone component of A. planipennis. This is the first contact sex pheromone identified in the Buprestidae.     

Mating behaviour in a slave-making ant, Rossomyrmex minuchae (Hymenoptera, Formicidae)

The mating behaviour of the ant Rossomyrmex minuchae, a rare, protected slave-making species in Spain, seems to be significantly affected by its particular life history and patchy habitat. The mating behaviour of the entire genus Rossomyrmex is virtually unknown. We present here the results of a 3-year study of mating behaviour in R. minuchae.Behavioural observations and limited nest excavations revealed that R. minuchae does not produce sexuals every year, the number of sexuals is low, and the sex ratio tends to be female biased. Females typically exhibit two distinct activity periods. The first, the mating period, takes place in early afternoon: the ants call near the natal nest, mate and then return to their nest. The second, the dispersal period takes place in late afternoon: the mated females exit their nest and fly in search of a new, non-parasitized Proformica longiseta host nest. Males are highly active during the mating period, but will remain inactive in the dispersal period even if experimentally presented with virgin females. It appears that females are monogamous, while males are polygamous. When males are late arriving at the female calling site, the females will frequently congregate presumably calling in chorus.The low reproductive efficiency exhibited by R. minuchae, coupled with the postulated low genetic variation in the population, as sisters may mate with the same male, could result in a low survival rate and risk of eventual extinction. The observed decrease in nest density we observed during the 2004 season may be indicative of such a process.     

Intercontinental chemical variation in the invasive ant Wasmannia auropunctata (Roger) (Hymenoptera Formicidae): a key to the invasive success of a tramp species

Unicoloniality emerges as a feature that characterizes successful invasive species. Its underlying mechanism is reduced intraspecific aggression while keeping interspecific competitiveness. To that effect, we present here a comparative behavioural and chemical study of the invasive ant Wasmannia auropunctata in parts of its native and introduced ranges. We tested the hypothesis that introduced populations (New Caledonia archipelago) have reduced intraspecific aggression relative to native populations (e.g., Ilhéus area, Brazil) and that this correlates with reduced variability in cuticular hydrocarbons (CHCs). As predicted, there was high intraspecific aggression in the Brazilian populations, but no intraspecific aggression among the New Caledonian populations. However, New Caledonian worker W. auropunctata remained highly aggressive towards ants of other invasive species. The chemical data corresponded with the behaviour. While CHCs of ants from the regions of Brazil diverged, the profiles of ants from various localities in New Caledonia showed high uniformity. We suggest that in New Caledonia W. auropunctata appears to behave as a single supercolony, whereas in its native range it acts as a multicolonial species. The uniformity of recognition cues in the New Caledonia ants may reflect a process whereby recognition alleles became fixed in the population, but may also be the consequence of a single introduction event and subsequent aggressive invasion of the ecosystem. Chemical uniformity coupled with low intraspecific but high interspecific aggression, lend credence to the latter hypothesis.     

Olfactive detection of fig wasps as prey by the ant<Emphasis Type="Italic"> Crematogaster scutellaris</Emphasis> (Formicidae; Myrmicinae)

In the species-specific and obligate mutualism between the fig (Ficus carica) and its pollinator (the fig wasps Blastophaga psenes), a third participant, the ant Crematogaster scutellaris, is a predator of the wasps. Here, we ask how ant workers can rapidly localise such prey, whose availability is limited in time and space. Using a Y-tube olfactometer, we tested ant response to odours emitted by different types of figs (receptive female, ripe female or male figs) and by fig wasps (pollinators or non-pollinators). We demonstrate that ants were significantly attracted only to odours emitted by pollinators, either alone or associated with odours of male figs (releasing wasps). Detection of prey odour by ants is an important trait that can explain their observed high rate of predation on pollinators, and could have important implications on the stability of the fig/fig wasp mutualism.