Data for synergistic and antagonistic interactions between Varroa destructor mites and neonicotinoid insecticides in male Apis mellifera honey bees

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 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 effect the number of sexually
mature adult drones available for mating.