Matthew F. Sledge

Cuticular hydrocarbons and reproductive status in the social wasp Polistes dominulus

Abstract. Most species of social insect are characterized by a reproductive division of labor among morphologically specialized individuals. In contrast, there exist many species where all individuals are morphologically identical and dominance relationships determine which individuals mate and/or reproduce. In newly founded multiple-foundress associations of the social wasp Polistes dominulus, foundresses establish dominance hierarchies where the top-ranked (alpha) female monopolizes egg laying. The possibility that chemical cues are used for recognition of egg-laying individuals has not been explored in this wasp. Using non-destructive techniques, we examined the relationship between ovarian activity and the proportions of cuticular hydrocarbons of three female types (dominant and subordinate foundresses and workers) in 11 colonies. Immediately after nest foundation, no differences were found between alpha and subordinate females. In contrast, at worker emergence, alpha females were statistically distinguishable from both subordinates and workers. We experimentally removed the alpha female in 5 of the original nests and reanalyzed hydrocarbon proportions of the new dominant individual. Replacement individuals were all found to acquire a cuticular signature characteristic of the alpha female. This suggests that cuticular hydrocarbons are used as cues of ovarian activity in P. dominulus, and we discuss our results in terms of a switch from behavioral dominance to chemical signaling in this wasp.

Worker rank, reproductive status and cuticular hydrocarbon signature in the ant, Pachycondyla cf. inversa

Abstract. Workers in de-queened colonies of the neotropical ant, Pachycondyla cf. inversa, form linear or near-linear dominance hierarchies by violent antennation and biting. In these rank orders, social status and ovarian activity are on average highly correlated. Whereas the presence of a fertile queen appears to be sufficient to prevent workers from laying eggs, fertile workers do not completely control reproduction by their nestmates, suggesting that workers are able to differentiate between an egg-laying queen and an egg-laying worker. Here we show that the composition of cuticular hydrocarbons of egg-laying workers is quantitatively and qualitatively different from that of non-laying workers and resembles the hydrocarbon blend of the queen but does not completely match it. Furthermore, using discriminant analysis, it was possible to distinguish workers with four different classes of ovarian development based only on their cuticular hydrocarbon profiles. Fertility-associated changes in cuticular hydrocarbons may play an important role in the behavioural regulation of reproduction in this ant.

Social hackers: integration in the host chemical recognition system by a paper wasp social parasite.

Abstract Obligate social parasites in the social insects have lost the worker caste and the ability to establish nests. As a result, parasites must usurp a host nest, overcome the host recognition system, and depend on the host workers to rear their offspring. We analysed cuticular hydrocarbon profiles of live parasite females of the paper wasp social parasite Polistes sulcifer before and after usurpation of host nests, using the non-destructive technique of solid-phase micro-extraction. Our results reveal that hydrocarbon profiles of parasites change after usurpation of host nests to match the cuticular profile of the host species. Chemical evidence further shows that the parasite queen changes the odour of the nest by the addition of a parasite-specific hydrocarbon. We discuss the possible role of this in the recognition and acceptance of the parasite and its offspring in the host colony.

Use of a simple method for sampling cuticular hydrocarbons from live social wasps

The classical methods of cuticular hydrocarbon extraction in insects involve the use of solvents and therefore the killing of specimens. We describe here a simple and inexpensive method that allows for the sampling of cuticular hydrocarbons from live social insects in the field. We compare the results of our method with those of the classical solvent extraction method, as well as those of solid phase micro-extraction (SPME), and show that the method is both reliable and suitable for use in the natural environment. We describe for the first time the cuticular compounds of the social wasp Polistes nimphus.

Behavioural assays testing the appeasement allomone of Polyergus rufescens queens during host-colony usurpation.

The role of decyl butyrate (the main component of the secretion of Dufours gland in newly-mated queens) during host-colony usurpation was investigated in the European amazon ant Polyergus rufescens. The effect of this ester on the behaviour of workers of the common host species Formica cunicularia was analysed. We used a laboratory aggression test during which workers of the species Camponotus ligniperda, masked with synthetic decyl butyrate, were introduced into colony fragments of F. cunicularia. The results showed that this compound drastically lowers the degree of overt aggression against the introduced ants, and we suggest that it acts as an appeasement allomone. Moreover, pieces of filter-paper soaked with decyl butyrate were more attractive than pieces of paper treated with solvent. The results are discussed in relation to a chemical strategy that likely allows an easier invasion and usurpation of host colonies by queens of this obligatory slave-making ant.

Use of solid-phase microextraction in the investigation of chemical communication in social wasps

Solid-phase microextraction has been used to investigate chemical communication in several social wasp species. Using the technique to analyse exocrine gland secretions, we demonstrate that the results are comparable with those obtained with the more classical methods that use solvents, eliminating, in many cases, the shortcomings of these methods in insect pheromone analysis. As a result of its simplicity this technique is very suitable for research on the chemical ecology of social wasps, and on insect communication in general.

Alarm communication in Ropalidia social wasps

SummaryAlarm pheromones, chemical substances produced by social insects to alert the colony to threat, are the principal means by which colony defence is co-ordinated. We present the results of a study on alarm behaviour in 5 swarming species of wasps belonging to the genus Ropalidia. These species show a remarkably efficient strategy of alarm communication, including visual display and attack synchronization. We show that pheromones released from the venom gland play an important role in alarm recruitment in species belonging to the Ropalidia flavopicta group, but not in Ropalidia sumatrae. We analysed the contents of the venom reservoirs content of four of the studied species by gas chromatography-mass spectrometry. Glands were found to contain a complex mixture of volatile compounds as well as spiroacetals of higher molecular weight. Interestingly, despite all species producing similar chemical compounds from the venom gland, these were found to elicit alarm behaviour in only those species that build nest envelopes, suggesting a link between chemical release of alarm behaviour and the evolution of nest architecture in Ropalidia wasps.

Dufour’s gland contents of queens of the slave-making ant Polyergus rufescens and its host species Formica cunicularia

Dufour’s gland contents of the queens of the slave-making ant species Polyergus rufescens and its host, Formica cunicularia, were analysed by gas chromatography-mass spectrometry. In P. rufescens, the gland contains a mixture of several esters, one of which, decyl isobutyrate, was consistently present in large quantities (constituting more than 80% of glandular contents). Glandular contents in the host species, were found to be different, containing, in addition to two substances also found in P. rufescens, a mixture of acetates and several hydrocarbons. Decyl isobutyrate was not present. We discuss the possible role of these substances in the life history of P. rufescens.

Use of Dufour's gland secretion in nest defence and brood nutrition by hover wasps (Hymenoptera, Stenogastrinae).

Social wasps of the subfamily Stenogastrinae produce an abdominal secretion that is used in two distinct biological contexts. First, the secretion plays an important role in larval nutrition where it serves as a substrate in which food is placed by the adults for eventual consumption by the larvae. Second, in several species, females apply the same secretion to the substrate on which their nests are constructed, where it constitutes a sticky barrier that defends the immature brood from predation by ants. This paper describes for the first time ant guard construction behaviour of three species of stenogastrine wasps belonging to the genera Eustenogaster and Liostenogaster. The identification of compounds making up these secretions was also performed by gas chromatography-mass spectrometry. Ant guards and brood secretions were similar, with saturated and unsaturated long chain hydrocarbons and alcohols as major components. We further confirm that the glandular source of abdominal secretion is the Dufours gland. This gland contains the same hydrocarbons, and in the same proportions as ant guards and brood secretion. We discuss the fundamental importance of Dufours gland secretion in the social life of these wasps by comparing species with and without ant guards within the subfamily.

Epicuticular lipids and fertility in primitively social wasps (Hymenoptera Stenogastrinae)

Abstract.  Lipid cuticular profiles of females of four species belonging to three different genera of stenogastrine wasps are examined in connection with reproductive potential (relative ovarian development). Cuticular lipids may not only represent the cues for nestmate discrimination (already behaviourally ascertained in three of the same species), but also allow discrimination of fertile and non fertile individuals. Comparisons with more socially evolved insects are reported and discussed.