Influence of Indole-3-Acetic Acid on Cellular Immune Responses of Galleria mellonella L. (Lepidoptera: Pyralidae) and Pimpla turionellae L. (Hymenoptera: Ichneumonidae) in a host-parasitoid system

Abstract

The dietary effects of the well-known auxin member plant growth regulator, indole-3-acetic acid (IAA), on hemocyte counts and behavior of the model insect Galleria mellonella L. (Lepidoptera: Pyralidae) and its parasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) were examined. In vivo and in vitro experiments involved five treatments applied to larvae with doses of 50, 500, 1000, 5000, and 10000 ppm IAA and the controls. Total hemocyte counts increased at all applied IAA doses in G. mellonella whereas no effect was observed in P. turionellae. According to acridine orange-ethidium bromide double staining, none of the IAA doses affected the ratio of apoptotic and mitotic cells in vivo however a decrease in the number of late apoptotic cells at 1000 and 5000 ppm was observed at in vitro experiments in G. mellonella. An increase in the percentage of early apoptotic hemocytes at 1000 ppm and late apoptotic hemocytes at 500 ppm were determined in P. turionellae larvae. IAA also increased the ratio of mitotic hemocytes in the circulation of P. turionellae larvae at 50, 1000, and 10000 ppm. Changes in the encapsulation rate of Sephadex A-25 beads were not significant however the increase at 5000 ppm at 4th hour in non-melanized hemocytes was recorded as compared to the control. A strong decrease in melanization at 50 ppm and an increase at 50 and 1000 ppm in non-melanized bead count at 24 h were also observed. It can be concluded that IAA is inappropriate to use in combination with microbial control agents in IPM programs due to elevated hemocyte counts of the pest.