Abstract: The co-toxicity co-efficiency (CTC) of a series of mixtures of abamectin as a biological pesticide, and chlorpyrifos as a phosphate insecticide with low toxicity to mammals, were determined with respect to the leafminer Liriomyza sativae. CTC of these mixtures was equal to 165-234 and within a range of marked synergism. According to the maximum and submaximum of proper proportions of chlorpyrifos to abamectin, two synergistically mixed, 30% permeated formulations, WP-1 and WP-2, were manufactured. Field trials showed that both compounds were highly effective in controlling L. sativae larvae. At an application rate of 50g/667 m², the corrected mortalities of WP-1 and WP-2 after 3, 7 and, 11 days were 90.43%-91.71% and 87.09%-90.53% respectively; at 25 g/667 m², the corresponding control effects of WP-1 were 85.96%-88.28%; and at 37.5g/667m², the corrected mortality of WP-2 was 84.01%-85.38%. These synergistic mixtures were fast acting, had good residual performance and were economical to use. In addition, 30% WP-1 was also effective in controlling L. huidobrensis. The advantage of using WP over EC is that less toxic substances are released into the environment.

Key words: Liriomyza spp., control, chlorpyrifos, abamactin, synergism, mixture