Factors involved in the aggregation of Harmonia axyridis Pallas

Conference (2012, May 22)

In order to survive cold winters, the invasive multicoloured Asian ladybeetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae) forms large aggregations in dwellings to overwinter. The factors ... [more ▼]

In order to survive cold winters, the invasive multicoloured Asian ladybeetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae) forms large aggregations in dwellings to overwinter. The factors involved in the selection of aggregation sites remain misunderstood. The work presented herein focussed on the study of the chemical compounds involved in this phenomenon. Chemical and behavioural analyses highlighted that long-chain hydrocarbons lead congeners towards aggregation sites and ensure the cohesion of the cluster. Subsequently, physical factors were investigated. We studied the influence of (1) the density of individuals and (2) the quality of available shelters on H. axyridis decision to settle and aggregate under shelters. A binary choice experiment conducted in laboratory showed that the multicoloured Asian ladybeetles present a permanent aggregative behaviour, even during non-wintering conditions. These experiments also highlighted the existence of social interactions between individuals. All these results contribute to improve knowledge of this behaviour in H. axyridis and could be used in the design of species-specific traps in order to control infestations in dwellings. [less ▲]

Role of long-chain hydrocarbons in the aggregation behaviour of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

in Journal of Insect Physiology (2012)

The multicoloured Asian ladybeetles, Harmonia axyridis (Pallas), form large aggregations inside dwellings to survive cold winters, causing annoyances to householders from their number and sometimes the ... [more ▼]

The multicoloured Asian ladybeetles, Harmonia axyridis (Pallas), form large aggregations inside dwellings to survive cold winters, causing annoyances to householders from their number and sometimes the induction of allergic reactions. Migratory flight and macrosite choice of this species is well documented. H. axyridis shows a hypsotactic behaviour and a clear preference for contrasting visual elements. However, how the microsite is selected remains undocumented, although a better understanding of the implicated factors could lead to the development of new control methods for this pest. In this work, we have hypothesized that non-volatile compounds are involved in the microsite choice and the aggregation process of this beetle. Long chain hydrocarbons were identified inside aggregation sites, comprising saturated and unsaturated homologues. An aggregation bioassay was then conducted on overwintering individuals, highlighting the retention capacity of the previously cited compounds on the tested ladybeetles. Additional investigations have shown that H. axyridis males and females, originating from overwintering sites, deposit a similar blend of molecules while walking. A Y-shaped tube assay revealed that this blend is used by male and female congeners as cue, allowing individuals to orientate towards the treated side of the olfactometer. These results suggest the use of two different blends of long chain hydrocarbons by H. axyridis during its aggregative period, the first one to lead conspecifics towards aggregation sites (microsites) and the second to ensure the cohesion of the aggregation. These findings support the potential use of these blends, in association with volatiles, in the design of traps in order to control infestations of this species in dwellings. [less ▲]

Chemical and physical factors involved in the aggregation behaviour of Harmonia axyridis Pallas

Conference (2011, July 27)

Spatio-temporal patterns of preys and wastes moved by ants within the nests

Poster (2010)

Living in society in a restricted and confined nest implies important organisational issues. Ants have to control food supply for the whole colony as well as nest defence but they also have to manage ... [more ▼]

Living in society in a restricted and confined nest implies important organisational issues. Ants have to control food supply for the whole colony as well as nest defence but they also have to manage everyday life tasks such as waste rejection. Within the nest, ants are faced with different items that have to be used or rejected regarding colony needs. We study whether they can discriminate between three types of items (building material, nestmate cadaver or prey) and accordingly adapt the spatio-temporal distribution of these items. Therefore, we used colonies of the ant Myrmica rubra settled in a 2-dimensional space and introduced different items in the nest centre. We show that each item triggers a specific cascade of behaviour. We observed important differences in rejection time: building items were removed within a few minutes and cadavers after a few hours while preys could be kept in the nest for a day or more. Furthermore, the movement of items by ants leads to specific spatio-temporal patterns. Building items were removed with a straight trajectory from the centre to the exit of the nest. Ant cadavers that could bear pathogens showed a trajectory avoiding and moving away from larvae that are potentially more sensitive to diseases. The moving of preys headed an oscillating pattern: these items were alternatively taken on larvae for consumption and then moved away from them, until final rejection. This specific pattern may be due to the coupled effects of groups of ants acting alternatively to feed larvae and reject waste. In the case of cadavers and building items, only undertaking ants may be active. These results suggest that each ant is able to discriminate and interact with each other leading at the collective level to a complex cascade of behaviour. [less ▲]

A new case of consensual decision: collective movement in earthworms

in Ethology (2010), 115