Influence of temperature and relative humidity on the efficacy of thiamethoxam for the control of three stored product beetle species

Abstract

Laboratory bioassays were carried out in order to evaluate the effectiveness of thiamethoxam in different levels of temperature and relative humidity (r.h.) against three major stored-grain beetle species, the lesser grain borer Rhyzopertha dominica (F.), the rice weevil, Sitophilus oryzae (L.) and the confused flour beetle, Tribolium confusum Jacquelin du Val. Adults of the three species were exposed on wheat treated with thiamethoxam at 0.1, 1 and 5 ppm and under six different combinations of temperature (20, 25 and 30 °C) and r.h. levels (55 and 75%). Our study showed that the increase in temperature increased mortality in all insect species, particularly at the lowest concentration. For some of the combinations tested, the low r.h. seemed to play a significant role in thiamethoxam efficacy in the case of R. dominica. Moreover, of the species tested, T. confusum was found to be the least susceptible, while R. dominica the most susceptible. In general, thiamethoxam was found to be effective against all three species, at concentrations that are comparable with most commercially available grain protectants.