Application of synthetic sex pheromone for management of diamondback moth,Plutella xylostella, in cabbage

Over a 2-year period field trials were conducted to assess the potential to disrupt mating ofPlutella xylostella (L.) using a commercial rope formulat ion of a 70:30 mixture of (Z)-11-hexadecenal and (Z)-11-hexadecenyl acetate , two components of the sex pheromone of the female. Screened field cages w ere placed into blocks of cabbage which were either treated with the pherom one or left untreated. Different densities of P. xylostella pupae were plac ed into each cage and then larval and pupal counts were made of the subsequ ent generation. In addition, sentinel females at mating stations were place d in each cage to assess the influence of the pheromone on the ability of m ales to locate and mate with females. Likewise, we used pheromone traps to assess whether the pheromone treatment influenced the ability of males to l ocate a pheromone source. In both years larval and pupal populations, produ ced as a result of the original inoculation, did not differ between pheromo ne-treated and untreated fields. The effect of pheromone treatment on larva l and pupal numbers did not change with changes in inoculated P. xylostella density, however, the density of P. xylostella released caused significant differences in the density of the subsequent generation. No significant di fferences were detected between the number of sentinel female adult P. xylo stella that successfully mated in pheromone-treated fields compared with un treated fields. Significant differences in the numbers of male P. xylostell a caught in pheromone-baited traps occurred between pheromone-treated and u ntreated fields in the first trial of 1993, and in the first trial in 1994 but not in the second trial. Such differences are often thought of as indic ations of mating disruption, although our other data presented in this stud y and reports from other studies indicate this is not always the case. Prev ious studies on mating disruption of P. xylostella in larger scale field te sts have been performed but the results have been variable and often ambigu ous. Overall, our results indicate that mating disruption of P. xylostella with the present technology does not appear to work even under the very con trolled situations which we utilized to eliminate insect movement between p lots.