Cantharidin analogues and their attractancy for ceretopogonid flies (Diptera: Ceratopogonidae)

Several ceratopogonid flies are attracted to cantharidin and ingest it from both cantharidin-baits and from meloid beetles, one of the few known natural sources for cantharidin. Because meloids are absent in northern Bavaria, and certain canthariphilous flies of the genusAtrichopogon are temporarily associated with certain plants (Apiaceae, Aristolochiaceae), it was suggested that canthariphilous ceratopogonids might be generally attracted by chemically similar plant-derived compounds. At first the seasonal fluctuating attractancy, sex ratio and behaviour ofA. oedemerarum Storå was studied at cantharidin baits. Synthetic cantharidin analogues exhibited an attractancy forA. oedemerarum if the exo,exo-7-oxabicyclo2.2.1]heptane skeleton of cantharidin was associated with a 2,3-dicarboxylic anhydride or a 2,3--lactone. According to structure-activity studies, the analogues seem to fit best into the active site of the receptor if the carbonyl function of the -lacton is in the exo- and 2-position. This is the first report indicating that molecules other than cantharidin are attractive for canthariphilous insects.