Prey-specific contact kairomones exploited by adult and larval Teretrius nigrescens: A behavioural comparison across different stored-product pests and different pest substrates

Prostephanus truncatus is a serious exotic beetle pest of stored maize and cassava in Africa. Teretrius nigrescens is a classical biological control predator of this pest that was released into Africa in 1991. In previous work it was shown that adult T. nigrescens are arrested in the presence of dust and frass produced by P. truncatus feeding on maize, and both adult and larval T. nigrescens are arrested by solvent extracts of this dust/frass when presented on filter paper. The current study used these two complementary bioassay approaches to test crude dust/frass and then solvent extracts of the same materials. Results demonstrate that T. nigrescens adults are arrested more strongly by the dust/frass of P. truncatus than the dust/frass of six other beetle pests of stored grain. Similar behaviours are observed for responses of both adults and larvae to solvent extracts. However, extract of dust/frass from Sitophilus zeamais is repellent to adults and larvae of T. nigrescens. Collections of dust/frass from P. truncatus cultured on maize, cassava and an artificial maize substrate previously stripped of all hexane extractable compounds, are all shown to arrest adult T. nigrescens when presented in their crude form and to arrest both adults and larvae when presented as solvent extracts. These experiments demonstrate that P. truncatus produces a species-specific kairomone that is independent of the food or tunnelling substrate. Findings are discussed in the context of prey location, particularly in natural habitats.