Toxicity and sub-lethal effects of Vitex agnus-castus L. essential oil as a Juvenile hormone analog on Trogoderma granarium Everts (Coleoptera: Dermestidae)

The Khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) is a serious pest of grains such as wheat. In the present study, the lethal and sub-lethal effects of Vitex agnus-castus L. essential oil were studied against T. granarium first instar larvae. To investigate the sub-lethal effects, the first instar larvae were exposed to the LC30 concentration of the essential oil and the biological parameters of the surviving insects were determined. Vitex agnus-castus essential oil had high fumigant toxicity for first-instar larvae of T. granarium (LC50: 132.14 µl/L air). In addition, V. agnus-castus L. had low mortality time (LT50: 17.27 h), indicating rapid effects of the compound. The larval period of individuals who came from first instar larvae exposed to V. agnus-castus essential oil was significantly longer than control. Also, exposure to the sub-lethal concentration of the tested essential oil significantly reduced the survival of the immature stages, adults’ longevity, and reproduction of adult females. The net reproductive rate (R0), intrinsic rate of increase (r), and finite rate of increase (λ) in the population came from larvae exposed to the essential oil of V. agnus-castus essential oil were 4.02 eggs/female, 0.016 day-1 and 1.016 day-1, respectively, that was significantly lower than the control population (27.55 eggs/female, 0.055 day-1 and 1.056 day-1, respectively). Also, the mean generation time of the essential oil-treated population was about 22 days longer than the control population. According to our findings, V. agnus-castus essential oil is highly toxic to T. granarium larvae and appears to contain a Juvenile hormone analog that is useful for effective control of T. granarium populations in storage systems.