Interactions between natural populations of spiders and pests in cotton and their importance to cotton production in southeastern Queensland.

Abstract

A range of pest species taken as prey by four species of spider in S.E. Queensland cotton was established from field observational studies. A direct numerical relationship was established between two spiders ('Chiracanthium diversum' L. Koch and 'Oxyopes mundulus' L. Koch) and larval 'Heliothis' spp. and these were expressed as exponential functions. Similarly a direct numerical relationship between the other two spiders ['Achaearanea veruculata' (Urquhart) and 'Araneus theisi' (Walck) was not established between their prey and habitat. The importance of spiders in preventing crop loss was considered by relating the abundance of spiders feeding on 'Heliothis' spp. to fruit damage levels in unsprayed cotton. Damage thresholds were frequently exceeded despite predation by spiders and it was concluded that their predatory role would have to be supplemented to ensure economic yields.