Exposure to clothianidin and predators increases mortality for heptageniidae

https://doi.org/10.1016/j.aquatox.2022.106146Get rights and content

Highlights

  • Stenacron and Stenonema mayflies are sensitive to neonicotinoids like clothianidin.

  • Coexposure to clothianidin and invertebrate and vertebrate predators increased mortality of mayflies.

  • Predators and clothianidin exposure had a synergistic effect on mortality.

  • Sublethal exposure to clothianidin increased predation in mayflies.

Abstract

Neonicotinoids are a class of insecticide with global impacts on natural environments. Due to their high solubility, they are frequently found in stream ecosystems where they have the potential to impact non-target biota. While environmental concentrations are generally below lethal levels for most organisms, there are concerns that sublethal exposures can impact aquatic insects, particularly mayflies, which are highly sensitive to neonicotinoids. Because sublethal doses of neonicotinoids can reduce mobility in mayflies, exposure could indirectly increase mortality due to predation by impairing their ability to avoid initial detection or escape predators. We examined whether exposure to the neonicotinoid clothianidin at a concentration below the 96-h EC50 (7.5 µg/L), would increase the predation risk of Stenacron and Stenonema mayfly nymphs by larval southern two-lined salamanders (Eurycea cirrigera) or eastern dobsonfly nymphs (Corydalus cornutus) using a controlled laboratory experiment. For Stenacron, we found significant interactive effects between pesticide and dobsonfly exposure that increased the hazard ratio (HR). The HR assesses risk relative to a control population, in this case mayflies in similar experimental conditions but without exposure to neonicotinoids or predators. With the addition of clothianidin, the HR of mayflies exposed to a dobsonfly nymph significantly increased from 1.8 to 6.2 while the HR for those exposed to salamanders increased from 7.6 to 12.5. For Stenonema, the HR initially decreased due to dobsonfly exposure (1 to 0.3) but increased when clothianidin and dobsonflies were combined (0.3 to 1.6). Our study shows that aquatic exposure to clothianidin can increase mortality for aquatic insects through predator pressure. Such indirect effects associated with neonicotinoid exposure warrant further investigation to expand our understanding of pesticide impacts to aquatic systems.

Introduction

In the 30 years since their introduction, neonicotinoid insecticides have become the second most used type of pesticide (Jeschke et al., 2011). Due to their widespread application as a seed treatment for common crops such as corn and soybeans (Douglas and Tooker, 2015) and greater insect-specificity over previous insecticides (Simon-Delso et al., 2015), neonicotinoids have the potential to heavily imparct nontarget insect populations. While the full environmental consequences of neonicotinoid use remain unknown, studies have shown that they can be frequently found in aquatic ecosystems due to their high solubility (Finnegan et al., 2017; Morrissey et al., 2015; van Dijk et al., 2013). Most vertebrates are resistant to neonicotinoids due to their limited number of nicotinic acetylcholine receptors; however, insects and some crustaceans are susceptible to concentrations in the parts per billion range (Miles et al., 2017; Morrissey et al., 2015). Neonicotinoids stay fixed in the insect neural receptors upon binding and cause synapses to continuously fire, which results in muscle spasms, paralysis, and eventual death (Yamamoto et al., 1995). Imidacloprid was the first neonicotinoid developed in the 1980s with thiamethoxam, clothianidin, and many others following shortly after (Goulson, 2013; Jeschke et al., 2011). It is estimated that neonicotinoids are applied to over 115 million hectares in North America and are used extensively on other continents (Krupke and Long, 2015; van der Sluijs et al., 2015). Because of these factors, there are concerns over the potential ecological risk posed to streams in these agricultural areas (Cavallaro et al., 2019; Hladik et al., 2018, 2014; Nowell et al., 2018).

Macroinvertebrates show a range of sensitivities to neonicotinoids (Miles et al., 2017). The 48-h EC50 for crustaceans exposed to imidacloprid range from 43,000 µg/L for Daphnia magna to 570 µg/L for Ceriodaphnia dubia (Hayasaka et al., 2012). Meanwhile aquatic insects also show a wide range in sensitivity to clothianidin, with reported 48-h LC50s for Lestes unguiculatus (Odonata), Hesperocorixa atopodonta (Hemiptera), and Graphoderus fascicollis (Coleoptera) at 1200 µg/L, 600 µg/L, and 2.0 µg/L, respectively (Miles et al., 2017). For stream insects, some of the most sensitive species to the six neonicotinoids commonly found in streams come from the order Ephemeroptera (mayflies), with a mean 24–96-h EC50 of 3.9 µg/L (Morrissey et al., 2015). In general, mayflies are considered a highly vulnerable taxa in streams because they are sensitive to a variety of human pollutants including chemical contaminants, changes in dissolved oxygen levels or temperature, and excessive sedimentation. Mayflies are also important members of aquatic ecosystems, as they are key consumers of detritus and biofilms as well as prey items for larger invertebrates, fish, amphibians, and birds (Kraus, 2019). Thus, threats to this group can have significant community and ecosystem-level effects, both at higher and lower trophic levels (Cowan and Peckarsky, 1994; Schulz and Dabrowski, 2001).

Although numerous studies have examined the acute toxicity of clothianidin to mayflies, less is known about the indirect effects of pesticide exposure. Neonicotinoids have rarely been observed in streams at concentrations near the EC50 values calculated for most mayfly species. In the U.S. corn and soybean regions, the mean concentrations observed in streams are 0.0082 µg/L for clothianidin with maximum concentrations of 0.257 µg/L (Hladik et al., 2014), which remains an order of magnitude below the mean observed EC50 for mayflies (Morrissey et al., 2015). While direct toxicity is probably rare in the environment, neonicotinoids can have chronic effects at concentrations detected in streams. For instance, chronic exposure of the mayfly Neocloeon triangulifer to clothianidin concentrations as low as 0.280 µg/L reduced survival to emergence, the size of egg masses, and adult lifespan (Raby et al., 2018). Mayflies have also been observed to reduce movement prior to paralysis when exposed to low levels of neonicotinoids (Macaulay et al., 2021), which could reduce feeding behaviors and predator avoidance. Declines in growth, emergence, and respiration rates in response to neonicotinoids have been observed in other insect species, indicating similar effects might be present in mayflies (Pestana et al., 2009).

In addition to direct acute or chronic effects of neonicotinoids, there are indirect effects of pesticide exposure on species interactions such as predator-prey relationships (Relyea and Hoverman, 2006). There is growing evidence that pesticides can alter predation risk for invertebrate prey. For instance, imidacloprid exposure reduced predator avoidance behavior in the trichopteran Stericostoma vittatum (Pestana et al., 2009). Following exposure to the insecticides azinphos-methyl or fenvalerate, mayflies have been shown to increase their drift response, which increased predation risk by fish (Schulz and Dabrowski, 2001). This elevated drift response can be triggered in mayflies by imidacloprid within two hours of exposure (Beketov and Liess, 2008). Another study showed that exposure to the neonicotinoid thiacloprid increased predation on the mayfly Baetis rhodani by an amphipod predator Gammarus fossarum, which normally consumes degrading leaves (Englert et al., 2012). Collectively, these studies indicate that sublethal exposure to neonicotinoids can increase predation risk, both by increasing the effectiveness of existing predators and enabling new predators. This could be a mechanism whereby neonicotinoid presence in streams alters aquatic insect communities (Cavallaro et al., 2019).

We investigated whether acute exposure to the neonicotinoid clothianidin altered predation rates on two mayfly species (Stenacron interpunctatum and Stenonema femoratum). These species are considered relatively tolerant to organic pollutants compared to other local mayfly species (Lewis, 1974), and are common throughout the United States Midwest agricultural region, which is heavily impacted by neonicotinoids (Hladik et al., 2014; Nowell et al., 2018). Both mayflies fill a similar niche and can often be found on the same rock in a stream, although, based on our observation with these populations, Stenonema nymphs tend to grow larger than Stenacron nymphs. Our focal predators were larval southern two-lined salamanders (Eurycea cirrigera) and dobsonfly nymphs (Corydalus cornutus). These predators were selected because they co-occur with mayflies and likely have different susceptibility to clothianidin. As vertebrates, two-lined salamanders are likely less susceptible to neonicotinoids although no LC50 tests have been conducted. As a comparison, other amphibians (i.e. Rana), had a 48-h LC50 exceeding 165,000 µg/L for neonicotinoids (Feng et al., 2004; Miles et al., 2017). Dobsonflies (Megaloptera) have a mean 24–96 h EC50 to neonicotinoids of 700 µg/L (Morrissey et al., 2015). We hypothesized that exposure to clothianidin would increase predation risk for mayflies by both vertebrate and invertebrate predators. Because dobsonfly nymphs may also experience pesticide effects due to their greater sensitivity, we predicted that pesticide exposure would result in a smaller increase in hazard for the mayflies exposed to dobsonflies, than for those exposed to salamanders. We further predicted that, although Stenonema are slightly larger, both genera of mayflies would have a similar response to predators and pesticide due to their similar habitat, physiology, and ecological interactions.

Section snippets

Specimen collection

We collected Stenacron interpunctatum and Stenonema femoratum mayfly nymphs and first year predatory eastern dobsonfly nymphs (Corydalus cornutus) from Flint Creek, Indiana, USA (40.340889°, −87.051353°) on 30 August 2019 by picking them off rocks with soft forceps. The southern two-lined salamander larvae (Eurycea cirrigera) were collected as eggs at the same location on 16 May 2019 and raised in the laboratory on a diet of zooplankton and mayflies. The dobsonfly nymphs averaged 20.5 mm in

Results

For the first 2 days, clothianidin exposure without predators had no impact on the mortality of Stenacron mayflies (ANOVA, p = 0.09, Table 1) or for Stenonema (ANOVA p = 0.84, Table 2). At the end of the first 2 days, survival in the control treatments were 83% for Stenacron and 83% for Stenonema. By day 3 survival in the Stenacron control had dipped below 80% and by day 6 the Stenonema controls fell below 80%, possibly due to the starvation conditions of the experiment. At the end of the 14 d

Discussion

We examined the interaction of a common agricultural pesticide, clothianidin, and predators on heptageniid mayflies from a small rocky stream embedded in an agricultural landscape. We found that clothianidin increased mortality for mayflies exposed to predators, even before it had a direct lethal effects on the mayflies. Additionally, we found that the overall hazard associated with salamander larvae was greater than that of dobsonfly nymphs, but contrary to our presumption that dobsonfly

Conclusions

This study indicates that exposure to clothianidin can increase predation risk in mayflies prior to the onset of pesticide-induced mortality. Indirect pesticide effects at these levels indicate that the ecologically impactful concentrations of pesticides may be lower than can be determined by the traditional single-species, single-stressor design of most toxicology experiments (Relyea and Hoverman, 2006). Even below EC50 levels, contaminants can interact with preexisting threats and other

CRediT authorship contribution statement

D. Riley Rackliffe: Conceptualization, Methodology, Investigation, Project administration, Writing – original draft, Formal analysis. Jason T. Hoverman: Conceptualization, Methodology, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Thanks to Purdue's Bindley Bioscience Center for assistance in quantifying pesticide concentrations. We also acknowledge the assistance of two peer reviewers for constructive advice in refining our analysis.

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