Population changes of spider mites (Acari: Tetranychidae) following insecticide applications in corn

Applications of 2 insecticides, methyl parathion and permethrin, for the control of 1st- and 2nd-generation European corn borer, Ostrinia nubilalis (Hiibner), in corn, Zea mays (L.), were evaluated in 1992, 1993, and 1994 for their effects on the population densities of twospotted spider mites, Tetranychus urticae Koch, Banks grass mites, Oligonychus pratensis (Banks), and selected mite predators such as predatory mites, lady bird beetles, pirate bugs, predatory thrips, lacewings, and spiders. Results indicated that applications of permethrin during the last week of July or early August were associated with a significant increase in the population of twospotted spider mites. However, no consistent increases in the population of Banks grass mites were observed. Predator populations were generally low throughout the study period, and no significant changes in the population of identified predators were observed between pretreatment and posttreatment sampling.