Posttreatment temperature influences toxicity of insect growth regulators in Musca domestica.

Musca domestica is one of the major cosmopolitan pests in livestock facilities because it can be both a nuisance and a vector of pathogens to animals. Currently, treatment of animal manure with insect growth regulator (IGR) insecticides is among major practices to control M. domestica throughout the year over wide-ranging environmental temperatures. Fluctuation in daily or seasonal temperature is one of the most established factors impacting toxicity of insecticides against insect pests. In this study, the effect of posttreatment temperature (range, 20-36 °C) on the toxicity of eight IGRs: five chitin synthesis inhibitors (cyromazine, diflubenzuron, lufenuron, novaluron, triflumuron), two juvenile hormone analogs (methoprene, pyriproxyfen), and one ecdysone agonist (methoxyfenozide), was investigated against M. domestica. The toxicity of lufenuron and novaluron increased by 1.78 times over the range of 20-28 °C, and 2.25 and 1.83 times, respectively, over the range of 28-36 °C, with an overall increase by 4.00 and 3.26 times, respectively (i.e., positive temperature coefficient). In contrast, the toxicity of diflubenzuron, pyriproxyfen, and triflumuron decreased by 1.43, 1.89, and 2.10 times, respectively, over the range of 20-28 °C, and 1.70, 2.00, and 1.95 times, respectively, over the range of 28-36 °C, with an overall decrease by 2.43, 3.78, and 4.10 times, respectively. The toxicity of cyromazine, methoprene, and methoxyfenozide did not change significantly. Overall, these data will help stakeholders to choose appropriate insecticides for M. domestica control depending on the prevailing environmental temperature and to avoid misuse of insecticides that ultimately lead to environmental safety.