Response of flea beetles,Phyllotreta spp., to mustard oils and nitriles in field trapping experiments

Trapping experiments were carried out near Winnipeg, Canada, in the spring of 1987 and 1988 to test attraction of crucifer-feeding flea beetles to volatile glucosinolate (GS) hydrolysis products released from glass vials. Nine isothiocyanates (IC) or mustard oils and three nitriles (CN) were tested. The pattern of attraction was the same for both flea beetle species,Phyllotreta cruciferae, andP. striolata. Captures in traps baited with allyl IC increased as release rates increased from 0.04 mg/day to 40 mg/day. The lowest rate that attracted large numbers of beetles was 4 mg/day; therefore this rate was used for further experiments. More beetles were captured in traps baited with allyl IC than with any other compound. In 1988 only, four IC in addition to allyl IC were attractive to both species; namely, benzyl IC, ethyl IC, and a mixture of ethyl and methyl 4-isothiocyanatobutyrate (ICB). When captures of the two species were pooled, 3-methylthiopropyl IC, methyl ICB, andn-butyl IC were also found to be significantly attractive. Nitriles were the least attractive compounds. The high release rates of mustard oils required to attract flea beetles indicate that fields ofBrassica crops would release sufficient quantities of IC to attract flea beetles from a distance but individual or small groups of plants normally would not. It is concluded thatBrassica varietal resistance to flea beetles is unlikely to be affected by manipulating IC release.