Time-dependent mortality and behavioral response of Odontotermes obesus (Blattodea: Termitidae) against different dose rates of pesticides for sustainable forest management

Abstract

Termites have become a global concern, and their effective management has remained a challenge since time immemorial. Certain microbial and botanical agents have been used for their management, but their efficacy has been compromised, particularly in field conditions. Hence, the current study was designed to check the efficacy of low doses of different pesticides, such as chlorpyrifos, fipronil, bifenthrin, and chlorantraniliprole, against mortality and behavioral responses of Odontotermes obesus at two different temperatures (16 ± 1 and 26 ± 1°C). The discrete behavioral symptoms included intoxication, ataxia, moribundity, and death. Laboratory-maintained termite workers were exposed to different concentrations of pesticides through a filter paper bioassay. All tested pesticides and their concentrations differed significantly regarding their lethal time (LT 50 ) values compared to the mortality of termite workers. Moreover, the LT 50 values of pesticides gradually decreased with increased pesticidal concentrations. Temperature also had a significant effect on the efficacy of tested pesticides as all pesticides showed better results at higher temperatures. At both tested temperatures, chlorantraniliprole (5 ppm) proved to be the most effective pesticide against termite workers. Similarly, the behavioral symptoms also varied depending on pesticides and their administered concentrations and existed for a relatively longer time span at lower temperatures. In most cases, the order of responses was moribundity, followed by intoxication and ataxia. Moribundity and intoxication were the most frequently observed symptoms for chlorpyriphos and bifenthrin-treated termite workers. In the case of fipronil, intoxication was the most pronounced symptom. Similarly, the maximum value of ataxia was recorded in the case of chlorantraniliprole. However, moribund symptoms lasted longer in all tested concentrations of chlorantraniliprole, followed by ataxia and intoxication. The overall order of toxicity was chlorantraniliprole > bifenthrin > fipronil > chlorpyrifos. These pesticides, at their low doses, did not exhibit any repellent action and were not detected by the foraging termite workers. Moreover, their slow action mechanism makes them a suitable candidate for infecting whole colonies away from treated surfaces. Therefore, these pesticides can be successfully incorporated into different integrated termite management programs to keep the plantation free from threatening underground pests.