Bimodal cue complex signifies suitable oviposition sites to gravid females of the common green bottle fly

Gravid females of the common green bottle fly,Lucilia sericataMeigen (Diptera:Calliphoridae), readily locate recently deceased vertebrates as oviposition sites, particularly when these animals have been injured. We investigated semiochemical and visual cues that mediate attraction of gravid females to fresh rat carrion. Female flies were more strongly attracted to incised rat carrion than to intact carrion. They were also attracted to Porapak Q headspace volatile (HSV) extract of incised rat carrion. Analyzing aliquots of Porapak QHSVextract by gas chromatographic‐electroantennographic detection revealed nine components [phenol,para‐ and/ormeta‐cresol (could not be separated), guaiacol, dimethyl trisulfide (DMTS), phenylacetaldehyde, (E)‐2‐octenal, nonanal, and tetramethyl pyrazine] that consistently elicited responses from blow fly antennae. In laboratory experiments, a synthetic blend of these nine components was as attractive to gravid females as Porapak QHSVextract, but blend attractiveness was due entirely toDMTS. In both laboratory and field experiments, increasing doses ofDMTSattracted increasingly more flies. Coupled withDMTS, carrion‐type color cues (dark red, black) were more effective than bright color cues (white, yellow) in attracting flies. In field experiments, dark traps baited withDMTScaptured a total of 214 calliphorid flies (200L. sericata, 10Lucilia illustrisMeigen, threeCalliphora vicinaRobineau‐Desvoidy, oneCalliphora vomitoriaL.), all of which were gravid females. These results support the conclusion thatDMTSand dark color represent a bimodal cue complex that signifies suitable oviposition sites to gravid calliphorid females, particularlyL. sericata.