Investigation of attraction of raspberry cane midge, Resseliella theobaldi,to volatiles from wounded raspberry primocanes
Abstract: Mated females of raspberry cane midge (Resseliella theobaldi) (Cecidomyiidae) areknown to be strongly attracted to odours from recently split raspberry primocanes. Fresh splitsare preferred over old ones suggesting the attraction is due, at least in part, to volatile chemicalsproduced. Using solid-phase microextraction (SPME) to sample the volatiles in situ it was shownthat a characteristic suite of chemicals was produced after splitting, and these were similar forfive varieties of raspberry. The components were identified and the 18 most abundant wereselected for further study, including six produced by intact stems and 12 produced after splitting.Of these, four elicited EAG responses from the antenna of a female R. theobaldi midge, includingthree from the group produced only after splitting. For field studies exclusion of the leastabundant compounds gave a reduced set of 13 compounds and it was shown that dispensing fourof these from a polyethylene vial and the other nine from a polyethylene sachet gave a reasonableapproximation to the blend observed from raspberry canes after splitting. Field trapping studieswere carried out in Hungary and the UK during 2009 and 2010 and these have given variableresults. In general, numbers of female R. theobaldi trapped were very low, although significantnumbers were caught in the test in Hungary during 2010. At two sites in Hungary and one in theUK during 2009, more males were caught in traps baited with the synthetic cane volatiles than inunbaited traps. At one of these sites numbers caught with the cane volatiles were similar to thosecaught with the sex pheromone. At two other sites in the UK numbers of male R. theobaldicaught with the cane volatiles were significantly less than those caught in unbaited traps. Theformer three sites were all open-field while the latter two were covered and it was thought thatthis factor might be affecting the performance of the synthetic lures. However, these results couldnot be repeated in 2010. Numbers of male R. theobaldi caught in traps baited with the totalvolatile mixture were not greater than those caught in unbaited traps in either Hungary or the UK,although a reduced blend of the four most volatile compounds showed some attraction to malesin the UK. Although considerable progress has been made, further work in both laboratory andfield is required. The development of lures attractive to gravid female R. theobaldi would providepowerful new tools for monitoring and control of this pest.