Synergistic and Antagonistic Interactions Between Varroa destructor Mites and Neonicotinoid Insecticides in Male Apis mellifera Honey Bees

Selina Bruckner,Peter Neumann,Geoffrey R Williams,Lars Straub

doi:10.3389/fevo.2021.756027

Selina Bruckner, Peter Neumann + Show 2 more

Open Access

https://doi.org/10.3389/fevo.2021.756027

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Abstract

Pressures from multiple, sometimes interacting, stressors can have negative consequences to important ecosystem-service providing species like the western honey bee (Apis mellifera). The introduced parasite Varroa destructor and the neonicotinoid class of insecticides each represent important, nearly ubiquitous biotic and abiotic stressors to honey bees, respectively. Previous research demonstrated that they can synergistically interact to negatively affect non-reproductive honey bee female workers, but no data exist on how concurrent exposure may affect reproductive honey bee males (drones). This is important, given that the health of reproductive females (queens), possibly because of poor mating, is frequently cited as a major driver of honey bee colony loss. To address this, known age cohorts of drones were obtained from 12 honey bee colonies—seven were exposed to field-relevant concentrations of two neonicotinoids (4.5 ppb thiamethoxam and 1.5 ppb clothianidin) during development via supplementary pollen patties; five colonies received patties not spiked with neonicotinoids. Artificially emerged drones were assessed for natural V. destructor infestation, weighed, and then allocated to the following treatment groups: 1. Control, 2. V. destructor only, 3. Neonicotinoid only, and 4. Combined (both mites and neonicotinoid). Adult drones were maintained in laboratory cages alongside attendant workers (1 drone: 2 worker ratio) until they have reached sexual maturity after 14 days so sperm concentration and viability could be assessed. The data suggest that V. destructor and neonicotinoids interacted synergistically to negatively affect adult drone survival, but that they interacted antagonistically on emergence mass. Although sample sizes were too low to assess the effects of V. destructor and combined exposure on sperm quality, we observed no influence of neonicotinoids on sperm concentration or viability. Our findings highlight the diverse effects of concurrent exposure to stressors on honey bees, and suggest that V. destructor and neonicotinoids can severely affect the number of sexually mature adult drones available for mating.

Highlights

Stressors like habitat loss, climate change, pollution, and invasive species have resulted in widespread anthropogenic effects on ecosystems (Butchart et al, 2010; Geldmann et al, 2014)
The lowest body mass was recorded in V. destructor only drones, which was significantly different from the Control and Combined treatment groups
We investigated the potential effects of simultaneous pressure from neonicotinoid insecticides and V. destructor mites on adult male honey bee emergence mass and survival

Summary

Introduction

Climate change, pollution, and invasive species have resulted in widespread anthropogenic effects on ecosystems (Butchart et al, 2010; Geldmann et al, 2014). It is believed that pressures caused by multiple, possibly interacting, stressors are responsible for consistently high losses of managed western honey bee (Apis mellifera) colonies across the northern hemisphere (Kulhanek et al, 2017; Bruckner et al, 2019; Gray et al, 2019, 2020). Both biotic and abiotic stressors, such as poor nutrition, introduced parasites, heavy metals, and pesticides are blamed (Steinhauer et al, 2018). Diverse effects are observed, ranging from antagonistic parasitic-pesticide interactions to synergistic pesticide-pesticide ones (Straub et al, 2020; Bird et al, 2021; Siviter et al, 2021)

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