Atividade inseticida de óleos essenciais de Citrus spp. sobre Sitophilus zeamais em milho armazenado

Abstract

Maize (Zea mays L.) is a cereal of great economic and social value. Its production is a world highlight, but there are significant losses caused by insect attacks. Among the insects that affect stored products, the coleopteran Sitophilus zeamais (Curculionidae) stands out, which causes damaging effects to the grain. In view of the indiscriminate use of synthetic insecticides to control insect pests, alternative methods are being increasingly studied, such as the use of plant compounds, particularly essential oils (EOs). The aim of this study was to assess the toxicity of the EOs of bitter orange (Citrus aurantium), sweet orange (Citrus sinensis), mandarin (Citrus reticulata) and bergamot (Citrus bergamia) on Sitophilus zeamais. The tests were carried out by contact and ingestion in order to estimate the lethal concentrations (LC50 and LC90) of each oil. Once the concentrations had been estimated, the repellency test was carried out with the LC50 on the insect. The four EOs were evaluated in the contact and ingestion test using different concentrations (0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 µL/20g) for a period of 48 hours, using 10 insects, 20g of maize, in 5 repetitions. In the repellency test, the lethal concentrations (LC50) of the four EOs were applied alone, using 10 insects, 20g of maize, in 10 repetitions, confined for 48 hours. In the contact and ingestion test, the percentages of insect mortality were counted and in the repellency test the insects attracted, as well as the number of adults that emerged in each treatment. In the contact and ingestion test, significant differences were observed at the lowest concentrations, with the most toxic EOs being bitter orange (C. aurantium) and bergamot (C. bergamia). The Repellency Index (RI) showed that the four EOs used had a repellent effect at all the concentrations tested. There was no significant difference in the emergence of S. zeamais on the treated maize kernels, indicating that they acted as oviposition inhibitors and/or had an ovicidal/larvicidal effect. Therefore, it was found that the EOs were promising for the management of S. zeamais in stored grain.