House flies (Musca domestica L.) are key pests of poultry and are managed
worldwide with a variety of insecticides. However, extensive and injudicious use of
insecticides has led to the development of resistance in many insect pests. Insecticide
mixtures can increase the efficacy of the product and/or delay the development of
resistance, thus making them a useful tool for pest control. In addition to their efficacy
when used alone, mixtures of emamectin benzoate, spinosad or nitenpyram with either
lambda-cyhalothrin or profenofos were assessed against a susceptible strain of house flies
collected from poultry farms. The analysis revealed that combination indices for
lambda-cyhalothrin/emamectin benzoate and lambda-cyhalothrin/spinosad mixtures
were significantly .1, indicating an antagonistic effect. In contrast, the indices for all
the tested ratios of lambda-cyhalothrin/nitenpyram were significantly ,1, suggesting
a synergistic effect. For mixtures containing profenofos, combination indices varied
significantly. For example, synergism was observed in a 1:1 mixture containing
lambda-cyhalothrin and emamectin benzoate, but antagonism occurred when a higher
proportion of the latter insecticide was used. Conversely, synergism in a mixture
containing profenofos and nitenpyram was observed only when a lower proportion of the
second insecticide was used. The present results suggest that ideal insecticide mixtures
must be empirically determined and alternative strategies such as mosaics, rotations and
cultural control should be considered for the management of the house fly.