Preliminary study of female-targeted semiochemical baits for the western corn rootworm in Europe

In recent years emphasis of semiochemical research on the western corn rootworm (WCR) (Diabrotica v. virgifera LeConte, Coleoptera, Chrysomelidae) shifted towards the development of more female-specific lures. Through identifying volatile compounds from maize silk, Hammack (J. Chem. Ecol., 27, 2001,1373) claimed that some combinations of the newly identified compounds were more powerful in attracting females than the conventional floral baits (based on 4-methoxycinnamaldehyde). Earlier we found that the newly developed 'hat' trap design (KLP) when baited with the floral bait was especially suitable for the capture of female WCR. Encouraged by this we set out to compare efficiency of female-targeted Diabrotica baits. None of the treatments tested captured females in higher percentage than the conventional WCR floral bait (4-methoxycinnamaldehyde + indole). The combination of beta-ionone + methyl salicylate + beta-caryophyllene (attractant found to be more female-specific in the USA previously) was not more attractive for females than unbaited controls. No other treatment produced significantly higher female percentages than the conventional floral bait. However, the conventional bait caught far more beetles than any of the other treatments. Electroantennographic responses from male or female antennae were very similar, suggesting that all 27 floral compounds tested were perceived similarly by the two sexes. The only exception was beta-ionone, to which females were slightly more responsive. It seemed that among the other compounds none showed potential for the development of a more female-specific lure. In conclusion, so far the most efficient female-targeted trap-bait combination for WCR in Europe is the conventional floral attractant applied in KLP traps.