Acute toxicity and sublethal effects of Artemisia sieberi Besser on digestive physiology, cold tolerance and reproduction of Trogoderma granarium Everts (Col.: Dermestidae)

Abstract

Trogoderma granarium, the Khapra beetle, is a major pest of cereal grains and nuts. In this research, the lethal and sublethal effects of Artemisia sieberi Besser essential oil (EO) was evaluated against 4th instar larvae of T. granarium under the laboratory conditions. Bioassays showed that the larvae were susceptible to both contact and fumigant toxicity. In contact and fumigant toxicity the calculated LD50 and LC50 were 44.3μg/cm2 and 33.5μL/L air, respectively. To assess the sublethal effects, 4th instar larvae were exposed to A. sieberi EO in contact (LD25 and LD50) and fumigant (LC25 and LC50) action. The larvae that exposed to LD50 of contact toxicity showed the lowest amylolytic activity (0.064±0.007mU/Individual) and intensity of bands. Control larvae had greater weight gain and consuming food compared to treated larvae. Furthermore, the highest and the lowest values of relative consumption rate (RCR) and relative growth rate (RGR) were observed on control (0.50±0.02 and 0.084±0.005mg/mg/day) and LD50 of contact toxicity (0.26±0.02 and 0.052±0.002), respectively. Insects exposed to EO had smaller amounts of protein, glycogen and lipid content than control. Survival rate of EO-treated larvae after exposure to low temperature showed that the potency of contact toxicity was higher than fumigant toxicity for decrease of cold tolerance. Finally, exposure to EO in larval stage reduced the pupal and adults weight, longevity of female, fecundity and fertility. Our findings showed that A. sieberi EO has significant potential for use in controlling T. granarium, in both contact and fumigant applications.