Another Mode of Action of Temephos Against Aedes aegypti Larvae: A Stomach Poison Investigation

Introduction: Aedes aegypti is a key vector for the spread of several severe arboviral infections. The Indonesian Ministry of Health launched Temephos as a national effort to limit the Aedes aegypti larvae population. The old theory has been passed down for generations that the principle of the mechanism of action of temephos as a neurotoxin. The main aim of this study was to investigate the mechanism of action of temephos as a stomach poison by using histopathology study. Method: There are two treatments with three replications: a container containing only 100 ml of water with tween 20 and a container containing 100 ml of water with 1 ppm of temephos 8G. The 20 third-instar Ae. aegypti larvae in containers containing 100 ml of water with 1 ppm of temephos 8G were compared with those in 100 ml of water containing Tween-20. The experiment was done in three replications. The number of dead larvae was recorded after 24 hours of treatment. Histological sections of the larval midgut were prepared and stained with hematoxylin-eosin (HE). Light microscopy was used to examine changes in the length of the midgut lumen and the epithelium. Data were analyzed using a one-way ANOVA. The appearances of the nucleus of the epithelial cell and the degree of damage were qualitatively observed. Results: The results showed that no dead larvae were found in the control group, however, 100% mortality was found in the temephos group. The changes in midgut lumen length and in the epithelium length were significantly different from those in the control group (p<0.05). Nuclei of epithelial cells were lost and midgut cells were damaged in the temephos group. Conclusions: This study reports the first discovery of the mechanism of action of temephos other than a neurotoxin, namely stomach poison