Repellency and Reduction of Offspring Emergence Potential of Some Botanical Extracts against Sitophilus zeamais (Coleoptera: Curculionidae) in Stored Maize

Abstract

Simple SummarySitophilus zeamais is an insect popularly known as maize weevil, usually found in corn, rice, wheat, oats, and barley, among other cereals. However, it is the biggest pest of stored grains which causes economic losses annually with a worldwide distribution. To control this insect, synthetic chemical insecticides are used, which, when misused, may be harmful to human health, animals, and the environment, and may cause resistance in these insect pests, making the insecticides lose efficiency. Therefore, studies that seek new control alternatives are important. In this study we investigated the effects of repellency and reduction of emerged insects of aqueous extracts of five plant species, S. terebinthifolius, L. sericea, L. tomentosa, L. longifolia, and L. nervosa on S. zeamais. Aqueous extracts from the leaves of each plant were used to treat corn kernels and thus assess whether they were capable of causing insect repellency. According to our study, the tested species cause repellency of S. zeamais, in addition to reducing the emergence of insects from the grain. However, this study is preliminary, and more studies are needed to verify that these botanical extracts are ecologically safe.Botanical repellents are, usually, considered safe to control Sitophilus zeamais, the main pest of stored maize, as they do not leave toxic residues in food, in addition to having lower costs than chemical insecticides. The aim of this study was to evaluate the repellency potential and the reduction of emerged offspring of botanical extracts, of Schinus terebinthifolius, Ludwigia sericea, L. tomentosa, L. nervosa, L. longifolia, and use them as botanical insecticides for S. zeamais. For the repellency test, arenas were set up, containing 50 g of maize kernels exposed to aqueous extract, besides a control treatment. At the center of each arena, 100 insects were released. After 48 h, the proportion of insects in the treated grains was determined. To test the effects of the extracts on insect mating and egg-laying, free-choice and no-choice tests were performed. Insects in both tests remained for ten days for mating and egg-laying. After this period, insects were removed to evaluate the offspring emergence. Sixty days after grain infestation, the number of emerged insects was counted. All selected botanical extracts demonstrated repellent action against S. zeamais, even after 48 h of application. The L. nervosa aqueous extract significantly reduced the emergence of S. zeamais.