Effects of heavy metal stress on free amino acids in the haemolymph and proteins in haemolymph and total body tissue of Lymantria dispar larvae parasitized by Glyptapanteles liparidis

Abstract

AbstractHeavy metal contamination of the forest pest insect Lymantria dispar (L.) (Lepidoptera; Lymantriidae), the gypsy moth, can alter its haemolymph composition, as has already been shown for carbohydrates and lipids in recent studies. L. dispar larvae are frequently parasitized by Glyptapanteles liparidis (Bouché) (Hymenoptera; Braconidae) larvae, which can — to some extent — regulate the population size of the pest insect. The parasitoids feed on the haemolymph of L. dispar larvae; hence, a different haemolymph composition of the host alters the trophic situation of the parasitoids. The aim of the present study was to investigate whether metal contamination also affects the concentrations of free amino acids in L. dispar haemolymph, and protein concentrations in their haemolymph and tissue. L. dispar larvae were parasitized on the first day of the second instar and then reared on diets contaminated with Cd, Pb, Cu or Zn at two concentrations each. Haemolymph and total body tissue of the larvae (fourth instar/third day) were analyzed. The concentrations of the free amino acids were elevated in five out of the eight contamination groups (Cd6, Pb4, Cu6, Cu10, Zn60), whereas haemolymph protein concentrations were significantly reduced in all contaminated individuals. The haemolymph protein concentration was 18 mg/ml in the control group and decreased to less than 10 mg/ml due to cadmium and zinc contamination at both concentrations and in the low copper contamination group. In contrast, total body proteins (136 μg/mg dry weight in the control group) were elevated due to heavy metal stress. Analyses of haemolymph protein concentrations during the fourth instar demonstrated an increase of the proteins from day one to day four (followed by a decrease on the fifth day) in the control group and the cadmium contamination group. A steady increase of proteins from the first to the fifth day in the copper and zinc contaminated larvae indicated a retarded development in these groups. Thus, the present study along with other recent studies demonstrated, that heavy metal stress changes the concentrations of all main haemolymph compounds of L. dispar larvae.