In Vitro Studies for the Evaluation of Insecticidal Potential of the Venom of Endoparasitic Wasp Aenasius arizonensis (Girault) (Hymenoptera, Encyrtidae)

Abstract

Aenasius arizonensis (Hymenoptera: Encyrtidae) a nymphal, solitary endoparasitoid is a potent biocontrol agent of cotton mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae). Female wasp injects a blend of secretions in its host during parasitization which alters the host physiology. Insecticidal potential of crude venom of A. arizonensis was evaluated along with its chromatographic fractions by microinjections bioassays in its natural host insect P. solenopsis at 3rd nymphal instars and adult. Host insects were treated with two different volumes of crude venom (0.3 and 0.5 µL) and RP-HPLC fractions of venom, while host insects with saline injections were used as control. Biological activity of the crude venom was also evaluated after heat and protease treatment. Maximum mortality (84.0 ± 2.91) of the host insects was observed at highest dose rate (0.5 µL) of the crude venom; while lowest mortality (71.0 ± 2.31) was recorded at lowest dose (0.3 µL) of venom applied on 3rd instar life stage. On the other hand, significant difference in mortality of four peaks of RP-HPLC venom fractions were recorded against 3rd instar larvae and adult when microinjections containing crude venom and fractionated venom. Our data confirms that crude venom of the wasp induces significant mortality against its host P. solenopsis. Whereas, no significant difference in mortality was observed for heat and protease treated venom, suggesting that bioactive component of the venom secretions of the wasp are proteins in nature, which lost their biological activity upon heat and protease treatments.