Histopathological damage to the external gills and midgut epithelial tissues spreadwing damselfly nymphs (Odonata: Lestidae) in response to the cyanobacterial toxin, microcystin

Cyanobacterial blooms produce a variety of toxins. These toxins can accumulate and become a major concerns for eutrophic and hypereutrophic systems. Toxicity studies have shown aquatic insects to be affected by these toxins. I examined the histopathological effects of Microcystin-LR on the epithelial tissues of the mid gut and the external gills of Amberwing Spreadwing Damselfly, Lestes eurinus nymphs (Odonata:Lestidae), as well as retention of the toxin within nymph tissues. Nymphs were exposed to six concentrations of Microcystin-LR, 0 μg L-1, 1 μg L-1, 10 μg L-1, 20 μg L-1, 35 μg L-1, 60 μg L-1. Exposure lasted 5 weeks. Half of the nymphs were examined for histopathological damage and stained using standard H&E staining. Histological slides were first digitized. The gut lining and external gills were examined for cell lyses and the percent tissue damage was compared to the exposure concentration. Regression analyses were run to determine the effects of increasing amount of the toxin on these two types of tissues. Nymphs were also analyzed using HPLC for amounts of Microcystin-LR that were taken up into the nymph’s tissues. These concentrations were compared to the exposure concentrations.