Food Shortage Amplifies Negative Sublethal Impacts of Low-Level Exposure to the Neonicotinoid Insecticide Imidacloprid on Stream Mayfly Nymphs

Julia G Hunn,Christoph D Matthaei,Samuel J Macaulay

doi:10.3390/w11102142

Abstract

Interactions of pesticides with biotic or anthropogenic stressors affecting stream invertebrates are still poorly understood. In a three-factor laboratory experiment, we investigated effects of the neonicotinoid imidacloprid, food availability, and population density on the New Zealand mayfly Deleatidium spp. (Leptophlebiidae). Larval mayflies (10 or 20 individuals) were exposed to environmentally realistic concentrations of imidacloprid (controls, 0.97 and 2.67 μg L−1) for nine days following five days during which individuals were either starved or fed with stream algae. Imidacloprid exposure had severe lethal and sublethal effects on Deleatidium, with effects of the lower concentration occurring later in the experiment. The starvation period had delayed interactive effects, with prior starvation amplifying imidacloprid-induced increases in mayfly impairment (inability to swim or right themselves) and immobility (no signs of movement besides twitching appendages). Few studies have investigated interactions with other stressors that may worsen neonicotinoid impacts on non-target freshwater organisms, and experiments manipulating food availability or density-dependent processes are especially rare. Therefore, we encourage longer-term multiple-stressor experiments that build on our study, including mesocosm experiments involving realistic stream food webs.

Highlights

Neonicotinoids have become the most commonly used insecticides worldwide [1,2]
The pesticides bind to the postsynaptic nicotinic acetylcholine receptors, resulting in continuous nervous system stimulation, which is lethal at sufficient concentrations [14,15]
Improving the ecological realism of ecotoxicological studies is crucial for providing the scientific knowledge needed to regulate pesticide use more safely in the future

Summary

Introduction

Neonicotinoids have become the most commonly used insecticides worldwide [1,2] Because they persist in soil for many months and are highly water-soluble [3], they enter freshwaters predominantly by leaching into groundwater and surface runoff after rain, with the latter causing high-concentration pulses in surface waters [4,5,6]. Neonicotinoids are neuro-active compounds that are highly specific to invertebrates, insects [13] This means they have been perceived as relatively safe for vertebrate wildlife, human consumers of treated crops and operators applying these pesticides to crops or seeds. This specificity means neonicotinoids pose a risk to non-target invertebrates.

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Conclusion