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1. Emerging investigator series: municipal wastewater as a year-round point source of neonicotinoid insecticides that persist in an effluent-dominated stream

   https://doi.org/10.1039/D1EM00065A  

   Webb, Danielle T. ; Zhi, Hui ; Kolpin, Dana W. ; Klaper, Rebecca D. ; Iwanowicz, Luke R. ; LeFevre, Gregory H. ( May 2021 , Environmental Science: Processes & Impacts)

   null (Ed.)

   Neonicotinoids in aquatic systems have been predominantly associated with agriculture, but some are increasingly being linked to municipal wastewater. Thus, the aim of this work was to understand the municipal wastewater contribution to neonicotinoids in a representative, characterized effluent-dominated temperate-region stream. Our approach was to quantify the spatiotemporal concentrations of imidacloprid, clothianidin, thiamethoxam, and transformation product imidacloprid urea: 0.1 km upstream, the municipal wastewater effluent, and 0.1 and 5.1 km downstream from the wastewater outfall (collected twice-monthly for one year under baseflow conditions). Quantified results demonstrated that wastewater effluent was a point-source of imidacloprid (consistently) and clothianidin (episodically), where chronic invertebrate exposure benchmarks were exceeded for imidacloprid (36/52 samples; 3/52 > acute exposure benchmark) and clothianidin (8/52 samples). Neonicotinoids persisted downstream where mass loads were not significantly different than those in the effluent. The combined analysis of neonicotinoid effluent concentrations, instream seasonality, and registered uses in Iowa all indicate imidacloprid, and seasonally clothianidin, were driven by wastewater effluent, whereas thiamethoxam and imidacloprid urea were primarily from upstream non-point sources (or potential in-stream transformation for imidacloprid urea). This is the first study to quantify neonicotinoid persistence in an effluent-dominated stream throughout the year—implicating wastewater effluent as a point-source for imidacloprid (year-round) and clothianidin (seasonal). These findings suggest possible overlooked neonicotinoid indoor human exposure routes with subsequent implications for instream ecotoxicological exposure. 

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2. Field-realistic exposure to neonicotinoid and sulfoximine insecticides impairs visual and olfactory learning and memory in Polistes paper wasps

   https://doi.org/10.1242/jeb.246083  

   Corcoran, Fiona E. ; Tibbetts, Elizabeth A. ( November 2023 , Journal of Experimental Biology)

   Exposure to insecticides may contribute to global insect declines due to sublethal insecticide effects on non-target species. Thus far, much research on non-target insecticide effects has focused on neonicotinoids in a few bee species. Much less is known about effects on other insect taxa or newer insecticides, such as sulfoxaflor. Here, we studied the effects of an acute insecticide exposure on both olfactory and visual learning in free-moving Polistes fuscatus paper wasps. Wasps were exposed to a single, field realistic oral dose of either low dose imidacloprid, high dose imidacloprid, or sulfoxaflor. Then, visual and olfactory learning and short-term memory were assessed. We found that acute insecticide exposure influenced performance, as sulfoxaflor and high dose imidacloprid exposed wasps made fewer correct choices than control wasps. Notably, both visual and olfactory performance were similarly impaired. Wasps treated with high dose imidacloprid were also less likely to complete the learning assay than wasps from other treatment groups. Instead, wasps remained stationary and unmoving in the testing area, consistent with imidacloprid interfering with motor control. Finally, wasps treated with sulfoxaflor were more likely to die in the week after treatment than wasps in the other treatment groups. Our findings demonstrate that sublethal, field-realistic dosages of both neonicotinoid and sulfoximine-based insecticides impair wasp learning and short-term memory may have additional effects on survival and motor functioning. Insecticides have broadly detrimental effects on diverse non-target insects that may influence foraging effectiveness, pollination services, and ecosystem function.

    

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3. Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies

   https://doi.org/10.3390/insects12110999  

   Prouty, Cody ; Barriga, Paola ; Davis, Andrew K. ; Krischik, Vera ; Altizer, Sonia ( November 2021 , Insects)

   Neonicotinoids are the most widely used insecticides in North America. Numerous studies document the negative effects of neonicotinoids on bees, and it remains crucial to demonstrate if neonicotinoids affect other non-target insects, such as butterflies. Here we examine how two neonicotinoids (imidacloprid and clothianidin) affect the development, survival, and flight of monarch butterflies, and how these chemicals interact with the monarch’s milkweed host plant. We first fed caterpillars field-relevant low doses (0.075 and 0.225 ng/g) of neonicotinoids applied to milkweed leaves (Asclepias incarnata), and found no significant reductions in larval development rate, pre-adult survival, or adult flight performance. We next fed larvae higher neonicotinoid doses (4–70 ng/g) and reared them on milkweed species known to produce low, moderate, or high levels of secondary toxins (cardenolides). Monarchs exposed to the highest dose of clothianidin (51–70 ng/g) experienced pupal deformity, low survival to eclosion, smaller body size, and weaker adult grip strength. This effect was most evident for monarchs reared on the lowest cardenolide milkweed (A. incarnata), whereas monarchs reared on the high-cardenolide A. curassavica showed no significant reductions in any variable measured. Our results indicate that monarchs are tolerant to low doses of neonicotinoid, and that negative impacts of neonicotinoids depend on host plant type. Plant toxins may confer protective effects or leaf physical properties may affect chemical retention. Although neonicotinoid residues are ubiquitous on milkweeds in agricultural and ornamental settings, commonly encountered doses below 50 ng/g are unlikely to cause substantial declines in monarch survival or migratory performance. 

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4. Acute exposure to sublethal doses of neonicotinoid insecticides increases heat tolerance in honey bees

   Gonzalez, V.H. ; Hranitz, J.M. ; McGonigle, M.B. ; Manweiler, R.E. ; Smith, D.R. ; & J.F. Barthell ( January 2022 , PloS one)

   The European honey bee, Apis mellifera L., is the single most valuable managed pollinator in the world. Poor colony health or unusually high colony losses of managed honey bees result from a myriad of stressors, which are more harmful in combination. Climate change is expected to accentuate the effects of these stressors, but the physiological and behavioral responses of honey bees to elevated temperatures while under simultaneous influence of one or more stressors remain largely unknown. Here we test the hypothesis that exposure to acute, sublethal doses of neonicotinoid insecticides reduce thermal tolerance in honey bees. We administered to bees oral doses of imidacloprid and acetamiprid at 1/5, 1/20, and1/100 of LD50 and measured their heat tolerance 4 h post- feeding, using both dynamic and static protocols. Contrary to our expectations, acute exposure to sublethal doses of both insecticides resulted in higher thermal tolerance and greater survival rates of bees. Bees that ingested the higher doses of insecticides displayed a critical thermal maximum from 2˚C to 5 ˚C greater than that of the control group, and 67%–87% reduction in mortality. Our study suggests a resilience of honey bees to high temperatures when other stressors are present, which is consistent with studies in other insects. We discuss the implications of these results and hypothesize that this compensatory effect is likely due to induction of heat shock proteins by the insecticides, which provides temporary protection from elevated temperatures 

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5. Neonicotinoids disrupt circadian rhythms and sleep in honey bees

   https://doi.org/10.1038/s41598-020-72041-3  

   Tackenberg, Michael C. ; Giannoni-Guzmán, Manuel A. ; Sanchez-Perez, Erik ; Doll, Caleb A. ; Agosto-Rivera, José L. ; Broadie, Kendal ; Moore, Darrell ; McMahon, Douglas G. ( December 2020 , Scientific Reports)

   Abstract Honey bees are critical pollinators in ecosystems and agriculture, but their numbers have significantly declined. Declines in pollinator populations are thought to be due to multiple factors including habitat loss, climate change, increased vulnerability to disease and parasites, and pesticide use. Neonicotinoid pesticides are agonists of insect nicotinic cholinergic receptors, and sub-lethal exposures are linked to reduced honey bee hive survival. Honey bees are highly dependent on circadian clocks to regulate critical behaviors, such as foraging orientation and navigation, time-memory for food sources, sleep, and learning/memory processes. Because circadian clock neurons in insects receive light input through cholinergic signaling we tested for effects of neonicotinoids on honey bee circadian rhythms and sleep. Neonicotinoid ingestion by feeding over several days results in neonicotinoid accumulation in the bee brain, disrupts circadian rhythmicity in many individual bees, shifts the timing of behavioral circadian rhythms in bees that remain rhythmic, and impairs sleep. Neonicotinoids and light input act synergistically to disrupt bee circadian behavior, and neonicotinoids directly stimulate wake-promoting clock neurons in the fruit fly brain. Neonicotinoids disrupt honey bee circadian rhythms and sleep, likely by aberrant stimulation of clock neurons, to potentially impair honey bee navigation, time-memory, and social communication. 

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