Prothoracicotropic hormone-producing neurosecretory neurons and antioxidative defense in midgut of Lymantria dispar in trophic stress

Abstract

As a very invasive insect species, Lymantria dispar is adaptable and sensitive to a changing environment. In insects the neuroendocrine system first reacts to stress by production of prothoracicotropic neurohormones (PTTH) that control ecdysteroid synthesis (morphogenetic and stress hormones). In this article, we report changes in the L2' brain neurosecretory neurons that synthesize PTTH in L. dispar larvae after feeding on locust tree leaves (Robinia pseudoacacia), an unsuitable host plant. Groups of larvae (n = 20 per experimental group) were offered this in comparison with oak leaves (Quercus robur), a suitable control diet, for 3 days after molting into the fourth instar. L2' neurons and their nuclei were enlarged and the amount of neurosecretory product in the cytoplasm was increased (15.5\%) after consumption of locust tree leaves in comparison to the control. Furthermore, activities of the following antioxidative defense components were estimated: superoxide dismutase (SOD), catalase (CAT), and amount of glutathione in the midgut. Higher SOD activity (13.85 +/- 0.9 U/mg prot.) and glutathione amount (0.56 +/- 0.06 mu MGSH/g tissue) but unchanged CAT activity was found in the midgut of larvae offered locust tree leaves when compared to the control.