BEHAVIOR, CHEMICAL ECOLOGY Volatiles Emitted From Eight Wound-Isolated Bacteria Differentially Attract Gravid Screwworms (Diptera: Calliphoridae) to Oviposit

Bovine blood inoculated with bacteria isolated from screwworm [Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae)]-infested animal wounds was tested as an attractant for oviposition for gravid screwworms. Eight species of gram-negative coliform (Enterobacteriaceae) bacteria mixed with bovine blood singly or all species combined and incubated for various times produced volatiles that attracted gravid ßies in a cage bioassay in varying numbers. In 15-min duration tests, volatiles from Þve species of bacteria (Klebsiella oxytoca, Proteus mirabilis, Proteus vulgaris, Providencia rettgeri, and Providencia stuartii) attractedmore females than volatiles of the three species (Enterobacter cloacae, Enterobacter sakazakii, and Serratia liquefaciens). In 1-h duration oviposition tests, volatiles from the substrate using the same Þve species of bacteria attracted more females to oviposit than the other three species. Volatiles from 24-h incubation period elicited least attraction andovipositionwhereasvolatiles fromthe48and72-h incubationperiod resulted in signiÞcantlymore attractionandoviposition.Attractionandovipositiondecreased signiÞcantlywhen the substrateswere incubated for 96 h. Volatiles from substrate with all species of bacteria combined attracted a significantly higher percentage of ßies to land and oviposit than those from substrates prepared with single species. It is possible thatmultiple active chemicals present in volatiles of the all-species substratemay act as synergists resulting in greater response than those observed with volatiles from single-species substrate. Before oviposition ßies took a bloodmeal from the oviposition substrate. It is possible that the oviposition is moderated by two different factors in screwwormÑÞrst, by using a chemical cue to land on a potential oviposition site and second, by using a bloodmeal to stimulate oviposition.