Lethal and sublethal effects of stored grains insects after the exposure to diatomaceous earth treated grains

Abstract

The management of stored grain pests is still highly dependent on the use of synthetic pesticides. However, concerns about possible contamination and the emergence of insect resistance are encouraging the search for safer control alternatives. Among these alternatives, diatomaceous earth (DE) has been drawing attention lately for causing various effects on pest insects, thus reducing the economic losses caused by these organisms in storage units. Different species of pest insects are negatively affected when exposed to DE, and a better understanding of the action of DE on different insects (e.g., susceptibility differences and behavioral differences) is necessary in order to establish and apply appropriate management strategies. Given the above, the present study takes an approach with investigations aimed at better understanding the differences in the lethal and sublethal effects of DE in two important stored pests, Sitophilus zeamais (M.) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae). In the first chapter we examined different effects of insects when exposed to DE-treated maize grains. Our results showed that survival, population growth rate and other factors (e.g., walking behavior, preference, grain intake, oviposition, etc.) are affected by exposure to DE. In addition, we verified differences in susceptibility of the studied species in which DE is more effective in controlling S. zeamais. In the second chapter we intensified the study of S. zeamais and S. oryzae exposure to DE now using treated rice grains and also evaluated the effect of sublethal exposure in male and female as well as the persistence of DE action. In addition to causing mortality and walking impairments, we observed that sublethal exposure to DE can cause harm to offspring and that sublethally exposed females appear to be more affected. Again, the S. zeamais species was more susceptible to DE. Thus, in the third chapter we sought to examine possible differences in the morphology, location, distribution and abundance of sensilla associated with the antennae and legs of S. zeamais and S. oryzae males and females. Some differences in sensilla length were observed for sex and species. Moreover, important interspecific differences were found for certain types of sensillae that were more abundant in S. oryzae and often were also more present in males. Overall, the results showed that DE is an efficient alternative for controlling Sitophilus spp., not only causing satisfactory weevil mortality,but also affecting other behaviors (e.g., walking, feeding, reproductive behavior, etc.). damage to the activity and development of these pests. Despite the effects on both species and although more experimentation is required, the most efficient results of DE in S. zeamais may be due to several factors such as the morphological differences found in the sensilla of the different species of Sitophilus spp. studied here, differences in responses and behavior of these species. Keywords: inert dust; grain storage; integrated pest management.