Evaluation and possible mechanism of beet armyworm (Spodoptera exigua Hubner) resistance to chlorpyrifos and their sensitivity to neem oil insecticides

The uncontrolled and excessive use of insecticides on Spodoptera exigua can cause resistance. The aim of this study is to test resistance of S. exigua to chlorpyrifos and determine the possible mechanism of resistance to S. exigua. The resistance assay was carried out on chlorpyrifos by determining the level of resistance by the comparison of LC50 between the field samples and the standard samples. The resistivity of S. exigua was correlated with the activity of acetylcholinesterase (AChE), esterase, and glutathione S-transferase (GST) enzymes. The samples of S. exigua were also tested for their sensitivity to neem oil insecticides. The results showed that S. exigua samples from Brebes and Cipanas had a resistance ratio (RR) of 5.50 and 3.26, respectively. The results of the present study indicate that the insensitivity of the AChE and the high activity of the GST play a significant role in the mechanism of S. exigua resistance to chlorpyrifos. However, the esterase has fewer roles in the S. exigua resistance mechanism for both samples. In addition, the results of neem oil insecticides test showed that S. exigua from Brebes and Cipanas samples is sensitive to the insecticide with the RR value less than 1; therefore, this biopesticide has the opportunity to manage resistant pests. A novel mechanism for insecticide resistance by insect was proposed.