Metallothionein level, non-specific esterases, fitness-related traits and integrated biomarker response (IBR) in larvae of Lymantria dispar L. (Lepidoptera) originating from unpolluted and polluted locations after chronic cadmium treatment

Long-term exposure of invertebrate populations to pollution might result in adaptations that must be taken into account when evaluating physiological parameters as biomarkers of contamination. In the present study we investigated whether previous exposure of gypsy moth, Lymantria dispar L. (Lepidoptera), population to pollution affects the sensitivity of larvae to cadmium treatment under laboratory conditions. Our goals in the current study were to compare metallothionein (MT) level and non-specific esterase activity including isoform expression in the midgut and fitness-related traits between caterpillars originating from polluted and unpolluted localities after chronic oral intake (50 and 100 µg Cd/g dry food). Besides being individually assessed as biomarkers of cadmium contamination, the responses of above parameters related to the midgut (MT concentration, specific activity of esterases and midgut mass) were summarized into the integrated biomarker response (IBR). Upon cadmium exposure, MT concentration increased significantly only in larvae originating from the polluted site, whereas non-specific esterase activity decreased in caterpillars from the unpolluted forest. We noticed similar patterns of esterase isoforms in both populations, including isoform number three that appeared only after exposure to the lower cadmium concentration. Midgut mass was reduced only in the group from the unpolluted locality exposed to the higher cadmium concentration. IBR index increased in a concentration-dependent manner in both populations, reflecting higher sensitivity of larvae from the unpolluted locality to the metal. Neither cadmium exposure nor population origin influenced larval survival. While MT concentration could be applied as a biomarker of cadmium exposure in populations that have been previously exposed to pollution for a longer time, non-specific esterase activity could indicate metal presence at unpolluted locations. IBR index and expression of esterase isoform number three could be used universally, regardless of the exposure history, except the latter might be limited to lower cadmium concentrations