Insecticidal effect of fungicide-coated maize kernels on larger grain borer, Prostephanus truncatus (Horn)

The effect of fungicides in maize kernels on adult mortality and progeny production of the larger grain borer, Prostephanus truncatus (Horn), was tested in a series of laboratory bioassays. These bioassays were carried out in vials containing different mixtures of untreated and fungicide-treated kernels with metalaxyl and prothioconazole using two populations of P. truncatus which originated from Tanzania and Ghana. The bioassays were carried out at two temperature levels, 25 and 30 °C. In general, the temperatures tested did not play a significant role in insect mortality, while, for both populations, the mortality rate increased with the percentage of coated kernels and the exposure time. For both populations, the progeny production in those vials that containing 50, 80, and 100 % fungicide-coated maize kernels was significantly lower than in the untreated. However, some differences between the tested populations emerged, the population from Tanzania was more susceptible to fungicide-treated kernels than that from Ghana. These results clearly suggest that fungicides can cause a considerable level of mortality on P. truncatus , which important in the case of the protection of maize kernels that are stored for use as seed. • Mortality of P. truncatus increased with percentage of fungicide-coated kernels and exposure time. • The temperatures 25 and 30 °C did not play a significant role in insect mortality. • Progeny from 50, 80, and 100 % fungicide-coated maize kernels was significantly lower than in the untreated. • Population from Tanzania was more susceptible than that from Ghana.