Impact of repeated pulse exposures on damselfly larvae

In this post, Alexander Feckler informs about their recently published paper “Repeated pulse exposures to lambda-cyhalothrin affect the behavior, physiology, and survival of the damselfly larvae Ischnura graellsii (Insecta; Odonata)”.

Damselfly larvae are known to be an important part of the aquatic food web, because of their roles as predators of small invertebrates (e.g., mosquito larvae) and prey for larger organisms. Due to their emergence, these organisms contribute to the energy flow from aquatic to terrestrial systems, where they represent a food source for terrestrial predators such as birds. Alterations in damselflies’ survival, growth, or physiology may thus translate into adverse effects in the food web structure and energy transfer within surface waters and across ecosystem boundaries. Against this background, it is worrying that damselflies’ aquatic habitats are threatened, with pesticides being one potential trigger for projected risks.

Ischnura graellsii larvae during size measurement at the beginning of the experiment (photo by S. Finotello)

Our study investigated sublethal effects on the damselfly Ischnura graellsii, namely changes in its lipid content, fatty acid composition, growth rate, and prey capture behavior (strikes against prey and capture success). Organisms were repeatedly exposed to 3-day pulses of the model pyrethroid insecticide lambda-cyhalothrin, followed by 4-day recovery phases in pesticide-free medium, to simulate frequent pesticide runoff events in the field. This pattern of exposure and recovery was repeated six times over 42 days.

The results showed that the lambda-cyhalothrin treatment did not strongly affect the number of strikes against prey. By contrast, damselflies’ capture success was reduced after exposure to the pesticide – a pattern that was not observed following recovery phases. Interestingly, the non-affected capture success following recovery phases did not seem to counteract the increased energy expenditures due to detoxification and defense mechanisms, since growth and lipid content were reduced upon lambda-cyhalothrin exposure. Furthermore, the content of two essential fatty acids and two of their precursors were negatively affected by lambda-cyhalothrin, possibly explaining the observed growth inhibition.

The present study thus showed that long-term exposure towards pesticide pulses could be seen as a major threat for the behavior and physiology of damselflies during their aquatic larval stage. Given their essential role in food web dynamics and energy transfer, such effects may translate into reduced local population sizes with subsequent bottom-up and top-down directed effects within and across ecosystem boundaries.

The paper authored by Simone Finotello, Alexander Feckler, Mirco Bundschuh and Frank Johansson is published in Ecotoxicology and Environmental Safety.