Effects of the cyanobacterial toxin, Microcystin-LR, on the morphology and development of the amber-winged spreadwing damselfly, Lestes eurinus (Odonata: Lestidae)

Cyanobacterial blooms produce significant amounts of hepatotoxins, which are major concerns for eutrophic and hypereutrophic systems. Toxicity studies have shown aquatic insects to be affected by these toxins, however the lethal range exceeds typical bloom concentrations. We examined the effects of Microcystin-LR on the Amber-Winged Spread Wing Damselfly, Lestes eurinus. 120 nymphs were divided evenly into six groups and then placed individually into 100ml of water containing different 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. In addition, half of the nymphs were given food that had been previously exposed to Microcystin-LR, the other half were given food that had never been exposed. Treatments lasted for 6 wk. We looked at three developmental aspects: Survivability, Developmental Time, and Fluctuating Asymmetry (FA). Survivability was significantly affected by the immersed concentration, with an LC50 of 40.1 μg L-1, however no differences in survivability occurred based on the food treatment. Mortality did not occur before the 5th instar and a significant proportion of mortality, approximately 77%, occurred within the final instar. Developmental time was not affected by the immersed concentrations but nymphs that received treated food took on average 10 days longer to reach final instar and 11 days longer to reach emergence. Finally, no significant differences in FA occurred based on either treatment. These data indicate that typical bloom conditions have high enough concentrations of extracellular microcystin to induce mortality in these large bodied aquatic insects.