Insecticide Resistance In Diamondback Moth, Plutella Xylostella L. (Lepidoptera: Yponomeuhdae) From Selected Cabbage Farms Associated With Pyrethroid And Organophosphate Use In Southern Ghana

Over dependence on insecticides for the control of diamondback moth (DBM), Plutella xylostella (L ) has resulted in development of resistant strains and health hazards due to toxic residues in cabbage. The present study was undertaken to evaluate resistance in DBM and to assess the contribution of residues of insecticides used for DBM control on resistance development. A preliminary survey conducted in Accra and Mampong-Akuapem, revealed inappropriate agronomic practices as the main cause of resistance development and health hazards due to insecticide residues on cabbage. Three pyrethroids viz lambda-cyhalothnn (pawa), cypermethrin (cypercal) and deltamethrin (deltaplan), an organophosphatechlorpyrifos (dursban) and a biopesticide- Bacillus thuringiensis (B.t.) (dipel) were selected for the study. Wild DBM pupae were sampled from three sites in Accra (Dzorwulu, Airport and Madina) and a site in Mampong-Akuapem. These populations were used to establish a DBM colony, which was reared on potted insecticide-free cabbage in a screen house. Early 4th instar larvae were used for leaf residue bioassays for B.t. and larvae immersion for organophosphate and pyrethroids. Compared to the recommended dosage the L C 9 5 of dursban were 106, 74, 193, 114 fold in DBM populations from Airport, Madina, and Dzorwulu and Mampong respectively. Similarly, for Pawa the LC95 to the recommended dosage were 103, 77, 100, 58 fold for Airport, Madina, Dzorwulu and Mampong respectively. In contrast, only 3-fold tolerance to dipel was recorded in Airport and Madina, 2 fold in Dzorwulu and 4 fold in the Mampong DBM populations The study revealed that most of the field-observed resistance among the conventional insecticides might be attributed to cross and multiple resistance.