MALLET, J; (1980) A laboratory study of roosting in the gregarious butterfly Heliconius melpomene. University of Newcastle-upon-Tyne: Newcastle-upon-Tyne, UK.

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Abstract

1) The gregarious roosting behaviour of a neotropical butterfly, H. melpomene, was studied under semi-natural conditions in a greenhouse insectary. 2) Some butterflies fly to the roost near sunset and rest, wings downwards, hanging on the tips of fine tendrils or twigs. The female position is slightly different to the male position, but some time after sunset the female position relaxes back to a male-like position. 3) Using videotape, it was determined that flying males and females hover at already roosted individuals of both sexes. Most of these pairwise interactions were of short duration, but males hovered at females for longer periods than found in any other pairwise interactions. In these male-female interactions, the behaviour of both individuals was similar to that in unsuccessful courtship during the day. In many interactions the insects exposed presumed pheromone disseminating structures. No matings were observed on the roost, and the outcomes of these interactions were not determinate. 4) Males and females roosted at similar times, but very young (callow) individuals roosted significantly earlier and interacted less than older individuals. 5) The time of 100% roost occupancy accurately tracked the time of sunset during the year. 6) The variation of the time of 100% roost occupancy around sunset was best explained by differences in light intensity due to changes in cloud cover on different evenings. 7) Near sunset, flying individuals approach dead butterflies or even crude models as well as live, roosted butterflies. It was found that a model that contrasts with its background is approached more readily than a non-contrasting model. 8) Photography showed that the undersides of many Heliconiini reflect ultraviolet light, whereas the uppersides absorb ultraviolet. 9) The adaptive value of the response to light intensity is discussed. 10) A possible mechanism of aggregation in Heliconius is discussed.

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