LABORATORY ASSESSMENT OF THE BEHAVIORAL-RESPONSES OF RESIDUAL POPULATIONS OF ORYZAEPHILUS-SURINAMENSIS (L) (COLEOPTERA, SILVANIDAE) TO THE CONTACT INSECTICIDE PIRIMIPHOS-METHYL BY LINEAR LOGISTIC MODELING

The behavioural responses of populations of an insecticide resistant and a susceptible strain of Oryzaephilus surinamensis (L.) to the contact insecticide pirimiphos-methyl were assessed in the laboratory. Adults were confined in insecticide treated (250 mg/m2) and untreated arenas containing a refuge filled with whole or kibbled wheat for a period of 1-7 days. Assessments of mortality/survival and the distribution of insects between refuge and arena was made each day. Results were analysed by a linear logistic modelling approach. This indicated that mortality was best described by logistic lines for each of the eight possible combinations of strain, treatment and diet. Differences between the 8 combinations of factors were quantified by calculating odds ratios for mortality for each day. The presence of food-filled refuges considerably reduced the mortality of both resistant and susceptible strains in insecticide-treated arenas. Mortality was always greater for both strains in treated arenas compared to untreated arenas. Diet was also an important factor in determining mortality/survival in treated and untreated arenas. For both strains whole wheat rather than kibbled wheat was an unfavourable diet in untreated arenas, and also for the susceptible strain in treated arenas. In contrast more resistant insects died in treated arenas containing refuges filled with kibbled wheat. Behavioural avoidance of the toxic arenas was observed with some insects from both strains when kibbled wheat was provided in the refuge and was most evident with the susceptible strain. There was no apparent evidence of avoidance behaviour when whole wheat was provided. These results provided no evidence of a link between physiological resistance and behavioural avoidance. The implications of these results in relation to the residual infestations of 0. surinamensis in grain and food stores are also discussed.