Seed oil from Syagrus coronata has contact toxicity and reduces population growth of Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract

The maize weevil, Sitophilus zeamais, is one of the main primary pests of stored grains in the world. Synthetic insecticides are the main means of controlling this pest, but environmental and health issues have been associated with their use. Therefore, natural insecticides have been sought to control pests like this. The objective of this work was to evaluate the insecticidal activity of fixed oil from S. coronata seeds (FOSc) against S. zeamais through ingestion and contact toxicity tests, influence on population growth rate and assessment of residual effect. The main compounds of FOSc were lauric acid (59.88%), myristic acid (13.13%) and capric acid (9.61%). FOSc presented ingestion toxicity with lethal concentrations for 50% (LC50) and 90% (LC90) of insects of 2.58 μL/g and 8.15 μL/g, respectively. The oil was able to inhibit in vitro α-amylase activity from gut extract. In the contact toxicity, LC50 and LC90 were 2.99 μL/g and 6.21 μL/g, respectively. Treating the grains with oil reduced the emergence of insects, reducing the population growth rate. However, FOSc showed low residual effect against the insect under study, being active only for 24 h after its application. In conclusion, S. coronata fixed oil can be used as an alternative to synthetic insecticides to control S. zeamais through ingestion and contact pathways.