Effects of Gibberellic Acid (GA3) on Biological Parameters and Hemolymph Metabolites of the Pupal Endoparasitoid Pimpla turionellae (Hymenoptera: Ichneumonidae) and its Host Galleria mellonella (Lepidoptera: Pyralidae)

Abstract

The non-target effects of the plant growth regulator gibberellic acid (GA₃) on host and parasitoid pre-adult development along with adult parasitoid longevity and size were examined using the endoparasitoid Pimpla turionellae (Hymenoptera: Ichneumonidae) reared on its host Galleria mellonella (Lepidoptera: Pyralidae) treated with different doses of the GA₃ in diet. Total protein, carbohydrate, and lipid content of hemolymph from parasitoid and host larvae were also evaluated with respect to GA₃ doses. Host development from egg to adult took 86-112 d. However, adult completed pre-adult development at an average of 34 d earlier than controls at the highest dose of 5,000 ppm. GA₃ treatment had the most significant effect on the egg-larval developmental time of host with more than 35% decrease at doses >1,000 ppm. GA₃ treatment did not affect the adult emergence time of parasitoids reared on hosts exposed to different doses. Adult longevity of wasps increased at 50, 100, and 200 ppm, whereas a decrease in longevity was apparent at 2,000 ppm with respect to controls. GA₃ treatment did not affect the adult length of wasps at doses ≤200 ppm however, a decrease in length was observed beyond 200 ppm but not at the highest dose 5,000 ppm. Hemolymph lipid at all and carbohydrate at most of the doses decreased in host larvae upon exposure to GA₃. The increase in hemolymph protein content of host larvae is likely to indicate a physiological adaptability to compensate for GA₃-induced stress. Total protein of wasp larvae fluctuated among treatment doses, was significantly lower at all doses except for the insignificant decrease at 2,000 ppm and increases at 50 and 200 ppm. Total lipid content of GA₃ treated groups increased significantly at only 100 ppm. Except for 100 ppm, there appeared insignificant decreases at doses ≤500 ppm and increases at doses >500 ppm. Total carbohydrate of wasp larvae increased at 100 and 1,000 ppm but decreased at 200 and 5,000 ppm. The potential significance of GA₃ on pest species and its natural enemy which may be used in Integrated Pest Management programs is discussed.