Atrazine exposure increases time until cannibalistic response in the widow skimmer dragonfly (Libellula luctuosa)

Abstract

Agricultural runoff containing herbicide is known to have adverse effects on freshwater organisms. Aquatic insects are particularly susceptible, and herbicide runoff has the potential to affect behavior in this group. Here we examine the effects of short-term exposure to the herbicide atrazine on cannibalistic behavior in larvae of the widow skimmer dragonfly (Libellula luctuosa Burmeister, 1839). Large larvae (>12 mm length) were exposed to concentrations of 0, 1, 10, or 100 μg/L atrazine for 96 h. A smaller (<8 mm) conspecific was then placed with the large larva and the behavior of the large larvae was observed for 30 min. Time until initiation of stalking and time until strike were determined. After the initial 30 min, each pair was checked at 2, 4, 6, 24, and 48 h. Time of consumption and amount consumed were determined. The number of larvae that engaged in cannibalistic activity within the initial 30 min observation period was significantly higher for controls compared with all experimental treatments. When stalking, striking, and consumption times were examined together (a measure of overall response time), concentration had a significant effect with the 10 μg/L group taking significantly longer to cannibalize than the control group. Cannibalism is a particularly important behavior in dragonfly larvae populations, and this study confirms that this interaction is altered by exposure to atrazine, with the potential to affect ecological relationships.