Environmental levels of neonicotinoids reduce prey consumption, mobility and emergence of the damselflyIschnura elegans

Abstract

1. Freshwaters are among the most endangered ecosystems in the world as a result of anthropogenic interference such as pollution. Pollution in the form of neonicotinoids has been intensively studied, but data thus far is often conflicted by contrasting responses between laboratory and field experiments. In addition, toxicity data are scarce and contradictory for insects such as Odonates (dragonflies and damselflies) and a potential risk to them may therefore be overlooked.2. We investigate the potential risk of neonicotinoids to Odonates by exposing nymphs of the blue-tailed damselfly Ischnura elegans to environmentally relevant concentrations of the neonicotinoid thiacloprid. We consider I. elegans as an indicator species for other Odonates as it is an abundant, widespread and eurytopic species. We analyse the effects of thiacloprid on multiple endpoints (survival, consumption, growth, molting, mobility and emergence), using cage-experiments as well as controlled field observations in naturally colonized experimental ditches.In addition, we assess sensitivity by either feeding the damselfly nymphs with lab-cultured prey or by letting them feed freely on natural aquatic invertebrates.3. All sublethal endpoints of I. elegans are affected to some degree, and strongly depend on the food offered; free-feeding nymphs are more sensitive than culturefed nymphs. Environmental relevant concentrations of thiacloprid strongly reduce the emergence of I. elegans and this effect is more substantial in the natural populations compared to the caged damselflies. This is likely explained by exclusion of additional biotic pressures such as predation in the caged experiment. 4. Policy implications. Literature reports that one out of seven Odonates is threatened and 24% of the species have declining populations. Our observations show that current risks of neonicotinoids to Odonates are underestimated in laboratory experiments as the toxicity is governed by multiple biotic factors such as food quantity/quality and predation. Given the widespread abundance of blue-tailed damselfly Ischnura elegans, the observed sensitivity to neonicotinoids and current | 2035 Journal of Applied Ecology BARMENTLO ET AL.

Experimental evidence for neonicotinoid driven decline in aquatic emerging insects

“…The responses of Coleoptera, Ephemeroptera, Trichoptera, and Odonata were all relatively straightforward: fieldrealistic neonicotinoid surface water concentrations reduced their abundance as well as their relative contribution to total emerged biomass. These results for the order of Odonata match the growing body of literature that show the negative effects of fieldrealistic neonicotinoid concentrations on Odonata species (22,41,44,45). Emergence of Coleoptera, Ephemeroptera, and Trichoptera were near absent at our highest test concentration, which is largely in line with results for thiacloprid of single species bioassays within these orders (30,46,47) and results from mesocosm experiments that assessed abundances of insect aquatic life stages (37,48).…”

“…Our results show that field-realistic levels of neonicotinoids in surface water negatively affect abundance and biomass of orders of major emerging insect orders. We provide evidence that more common neonicotinoid surface water concentrations (41) halve the species diversity of the most species-rich freshwater insect family, the Chironomidae. At the highest test concentration, Chironomidae diversity mostly dropped to a single species, while emergence of three other insect orders (Coleoptera, Ephemeroptera, and Trichoptera) was close to nonexistent.…”

Cross‐Ecosystem Fluxes of Pesticides from Prairie Wetlands Mediated by Aquatic Insect Emergence: Implications for Terrestrial Insectivores

“…The range of concentrations observed in the present study (1–572 ng total pesticide g –1 of insect) is similar to the range of neonicotinoid concentrations (114–548 ng g −1 ) in slugs that decreased feeding on them by predatory beetles (Douglas et al 2015). Food avoidance or reduced feeding is a common effect of consuming pesticide‐laden food that can lead to suboptimal outcomes for consumers (Douglas et al 2015; Barmentlo et al 2019; Calvo‐Agudo et al 2019; Eng et al 2019; Korenko et al 2019). However, it is difficult to say what kind of effects the potential exposures found in the present study would affect insectivores, including vertebrates, at our sites.…”

Physiological Effects of Neonicotinoid Insecticides on Non-Target Aquatic Animals—An Updated Review

“…The freely feeding damselfly emerged to be highly sensitive compared to culture fed damselflies. Accordingly, results depict neonicotinoids to perform a central role in the decline of odonate [65].…”