Role of cuticular hydrocarbons in the chemical recognition between ant species in the Pachycondyla villosa species complex.

Cuticular hydrocarbons (HCs) play important roles in insect communication but few studies clearly demonstrate the direct link between HCs and nestmate recognition. Therefore, cuticular lipids were extracted from ants, their HC and non-HC fractions as well as the three principal classes of HCs (n-alkanes, branched alkanes and alkenes) were purified and tested using an immobilizing "joust" device which allowed quantification of early pairwise behavioural responses, mandibular opening and antennal retraction, without occurrence of subsequent damages as in classic dyadic encounters. Chemical recognition of ants was studied at three levels of interactions (intra-colonial, intra-specific and inter-specific). Three closely related species already chemically characterized were used: Pachycondyla villosa (Pv), P. inversa (Pi) and P. subversa (Ps). Each species had its own behavioural responses. Moreover, responses of Pi and Ps towards Pv were significantly longer, than they were between themselves whereas Pv ants were equally aggressive towards Pi and Ps. These differences are in agreement with the results of the cluster analysis of the cuticular HCs profiles that place Pi closer to Ps. In support of the idea that components of cuticular lipids profiles are important for recognition, we found that only the HC fraction and its branched subfraction elicited a behavioural response of Ps workers. It is suggested that internally branched methyl- and dimethylalkanes are involved in recognition behaviour.

Hydrocarbon circulation and colonial signature in Pachycondyla villosa.

In ants, both cuticular and postpharyngeal gland (PPG) hydrocarbons (HCs) have been involved in nestmate recognition. However, no detailed comparison is available. A comparative study including also high density lipophorin (HDLp), an internal HC carrier, was therefore undertaken on Pachycondyla villosa. Purified HDLp is an 820 kDa lipoprotein with a density of 1.114 g/ml and two 245 and 80 kDa apo-proteins. Its hydrocarbon profile is very similar with the cuticular one, in agreement with its hydrocarbon carrier function. Conversely, n-alkanes and externally branched monomethylalkanes are markedly decreased in the PPG. According to their physical properties, this suggests that they are involved in waterproofing on the cuticle. The PPG actually contains only internally branched mono-, dimethylalkanes or monomethylalkenes; their greater fluidity is more adequate for chemical communication. The percentages of some of them are statistically not different between the cuticle and PPG. Their mixtures vary with colonies and they may thus be involved in colonial signature. A scheme for hydrocarbon circulation is discussed, involving lipophorin, cuticle, PPG and self-grooming in one individual, a pathway complementary or alternative to the selective delivery by lipophorin in some other insects. HCs are then distributed between nestmates' cuticles through allo-grooming and physical contacts.

Le système reproductif chez une ponérine sans reine: Dinoponera quadriceps santschi.

Thirteen colonies of Dinoponera quadriceps were studied in the field in Brazil. Dissection of all workers showed that each worker has ovaries with 6 ovarioles/ovary and a functional spermatheca. Moreover, the continuity of ovarian physiological states among workers is remarkable. Egg laying is performed by mated worker ( = gamergates) but also by few unmated ones exhibiting completely developed ovaries with numerous oocytes and yellow bodies inclusions. Besides, some gamergates present uncompletely developed ovaries and thus cannot be involved in egg laying until their ovaries reach full development. The role of both insemination and aging process in the differentiation between reproductive and non reproductive status is discussed.

Individual foraging in the antPachycondyla apicalis.

A model of individual foraging in social insects as presented that formalises the dynamics of foraging and concentrates on the collective rather than the individual benefit, quantifying the relationships between a colony's foraging area, number of foragers and foraging energy budget and the food sources' rate of arrival, disappearance and capture. A series of experiments, in which a number of prey were offered to colonies of the individually foraging antPachycondyla (ex-Neoponera) apicalis confirm the hypotheses implicit in the model and measured the rates of capture and competition. 60 days observation of 3P. apicalis colonies' foraging activity are summarised and used in conjunction with the model to obtain estimations of the density and rate of arrival of available prey in the foraging area. We examine how a colony's foraging benefit may be influenced by its foraging area, the number of foragers, and the forager/non-forager ratio and show that a colony's jocial structure strongly limits its potential foraging benefit. Within these limits,P. apicalis does not appear to be an optimal forager.

An automated photographic technique for behavioural investigations of social insects.

We describe a technique based on automatic photography as an alternative to the visual scanning method for behavioural investigations of insect societies. This technique opens up the possibilities for studying poorly-populated colonies over prolonged periods. The reliability of this technique as compared to the direct observational method was demonstrated on the basis of an investigation of the social organization of a neotropical Ponerine ant (Ectatomma ruidum ). The results obtained by the two techniques were very comparable both in regards to the overall behavioural profiles for the colony and as concerns the description of functional groups and sub-castes.