Rachid Hamidi

Dispersal strategies in the highly polygynous ant crematogaster (orthocrema) pygmaea forel (formicidae: Myrmicinae)

In ants, dispersal strategies and morphology of female sexuals are generally linked to the mode of colony founding. In species using long-range dispersal tactics, queen/worker dimorphism is generally high and young queens are able to initiate new colonies by themselves, using their metabolic reserves. By contrast, in species using short-range dispersal strategies, queen/worker dimorphism is generally low and, due to their limited metabolic reserves, queens have lost the capacity to raise their brood alone and to found their colony independently. Moreover, polygyny is also often associated with short-range dispersal strategies, although the relationship between the number of queens and the dispersal strategy in ants is not clear-cut. Here, dispersal strategies were investigated in C. pygmaea, a highly polygynous and polydomous ant species from northeastern Brazil. Field observations and laboratory experiments show that this ant exhibits a suite of traits that are more commonly associated with long-range dispersal and independent colony foundation: functional wings in both males and females, high queen/worker dimorphism, strong weight loss in mature queens, nuptial flights and, in the lab, ability of young queens to found new colonies in haplometrotic conditions. On the other hand, this species shows a high degree of polygyny with a strong seasonal component, and, at least under laboratory conditions, mature queens seem able to develop propagules if they are accompanied by at least 10 workers. These features strongly suggest that (1) some of the gynes do not engage in a long-range dispersal but become new queens in their mother colony and (2) that budding events are possible in this species. We therefore speculate that C. pygmaea has a dual dispersal strategy probably related to environmental conditions: some gynes engage in long-range dispersal followed by independent colony foundation at the beginning of rainy season, while others mate in the parental colony and are re-adopted leading to high polygyny. During the rainy season, budding events can lead to colony extension and increased polydomy. Polydomy is commonly thought to improve resource discovery and exploitation through decentralized foraging behavior, a significant advantage during the rainy season when food ressources (mainly floral/extrafloral nectaries and hemipteran honeydew) are more abundant and when colony needs for food supplies are highest.

Oviposition behaviour in Paysandisia archon (Lepidoptera: Castniidae)

Summary Paysandisia archon (Burmeister, 1880) (Lepidoptera: Castniidae) is a South American insect developing on palms and recently introduced in Europe where it damages most palm species. Understanding the oviposition behaviour would be decisive for risk assessment and pest management but key points on oviposition behaviour are missing. Using wind tunnel and field experiments, we investigated the oviposition timing, the attraction behaviour of mated females to palms and the different steps of oviposition behaviour. Results showed that oviposition behaviour occurred between 3 pm and 6 pm. In the field, gravid females were significantly more attracted by the palm crown than virgin females. The ovipositing females exhibited distinctive steps before ovipositing. Subsequent to alighting on the crown, pre-oviposition behaviour was characterized by two main behavioural steps: walking and probing the surface with antennae and ovipositor. After the choice of oviposition place, the gravid female remains motionless and the extendible ovipositor is deeply introduced into the upper fibrous part of the crown. About 10 eggs can be lays at the same place. Finally, the female starts to walk again and reinitiates the same behavioural sequences. This paper supports the hypothesis that odours from the crown may play a key role in gravid female attraction. The study assessed that P. archon lays on the palm crown, the part of the palm that should be treated for population monitoring.