LARVAL PREPUPATION BEHAVIOR OF DROSOPHILA-PAVANI, DROSOPHILA-GAUCHA AND THEIR RECIPROCAL HYBRIDS

The behavioural mechanisms by which the larvae of the sibling species D. pavani and D. gaucha, and their reciprocal hybrids select pupation sites are described in terms of larval substrate preferences. If the l arval behaviour of the parental species and their reciprocal hybrids d uring pupation leads them to pupate in different substrates, such pref erences could be used to identify environmental factors and genetic me chanisms involved in the evolution of that behaviour. Confronted with dry substrates, interspecific hybrid larvae pupated in the rearing cup , while the parental species pupated both outside and inside the cup. Like the parental species, the hybrids pupated outside, when humid sub strates surrounded the rearing cup. Larvae from D. pavani and D. gauch a showed a broader norm of reaction than the hybrids. D. pavani larvae occupied dry and humid substrates to pupate, while D. gaucha larvae t ended to prefer only humid substrates. Larvae of D. pavani burrowed in to dry sand pupated preferently in the deep layers of the substrate. F ew D. gaucha larvae burrowed; they tended to pupate in the upper layer s of dry sand. D. pavani larvae pupated on the moist sand, while most of D. gaucha larvae burrowed and formed puparia in the upper layers of the substrate. The hybrid larvae showed no burrowing behaviour in eit her dry or moist sand.