Acute Exposure to Worst-Case Concentrations of Amitraz Does Not Affect Honey Bee Learning, Short-Term Memory, or Hemolymph Octopamine Levels.

Amitraz, an acaricide used to treat Varroa destructor Anderson & Trueman, is one of the most commonly detected pesticides in honey bee (Apis mellifera L.) hives. Acaricides sometimes negatively impact honey bee cognition, but potential effects of amitraz on honey bee learning have been rarely studied. We topically exposed foragers to 95th percentile field-relevant levels of amitraz and, 24 h later, tested the ability of bees to associate a sucrose reward with a conditioned odor (learning response) using the proboscis extension response (PER). We then tested the ability of the bees to retain this memory 1 h and 2 h post-conditioning. Because amitraz is thought to affect octopamine metabolism in honey bees, and because octopamine is directly related to honey bee learning and memory, we also examined effects of exposure to amitraz on octopamine levels in honey bee hemolymph. We found that acute exposure to 95th percentile doses of amitraz had no impact on honey bee learning or short-term memory as measured by PER. Concentrations of octopamine in hemolymph from our low amitraz treatment were 1.4-fold higher than control levels, but other treatments had no effect. Our results from worst-case acute exposure experiments with worker bees in the laboratory suggest that typical field-relevant (within hive) exposures to amitraz probably have little effect on honey bee learning and memory.

A field study examining the effects of exposure to neonicotinoid seed-treated corn on commercial bumble bee colonies.

Neonicotinoid insecticides have been studied as possible contributors to bumble bee declines in North America and Europe. This has potential significance in corn agro-ecosystems since this crop is frequently treated with neonicotinoids and dominates much of the agricultural landscape in North America and Europe where bumble bees and other pollinators are commonplace. We conducted an experiment where commercial bumble bee (Bombus impatiens) hives were placed during pollen shed next to corn (Zea mays) fields that were grown from "conventional" seed that was treated with neonicotinoids, or "organic" seed that was not treated with pesticides. Samples of pollen were collected from corn plants for neonicotinoid residue analysis, pollen types carried by worker bees returning to hives were determined, and in autumn hives were dissected to measure various endpoints that serve as markers of colony vigor. Clothianidin was detected (0.1-0.8 ng/g) in pollen collected from all conventional fields, but was not detected in pollen from organic fields. Corn pollen was only rarely collected from bumble bee foragers and the vast majority of pollen was from wild plants around the corn fields. All hives appeared healthy and neonicotinoid seed treatments had no effect on any hive endpoints measured, except the number of workers, where significantly fewer workers were recovered from hives placed next to conventional fields (96 ± 15 workers per hive) compared to organic fields (127 ± 17 workers per hive). The results suggest that exposure during pollen shed to corn grown from neonicotinoid-treated shed poses low risk to B. impatiens.

Green peach aphid, Myzus persicae (Hemiptera: Aphididae), reproduction during exposure to sublethal concentrations of imidacloprid and azadirachtin.

BACKGROUND: Resurgence of insect pests following insecticide applications is often attributed to natural enemy disturbance, but hormesis could be an alternative or additional mechanism. Green peach aphid, Myzus persicae (Sulzer), is an important insect pest of many crops worldwide that may be exposed to sublethal insecticide concentrations over time. Here, the hypothesis that exposure to low concentrations of imidacloprid and azadirachtin can induce hormetic responses in M. persicae is tested in the laboratory. RESULTS: When insects were exposed to potato leaf discs dipped in sublethal concentrations of insecticide, almost all measured endpoints-adult longevity, F1 production, F1 survival and F2 production-were affected, and a statistically significant (P < 0.05) stimulatory response was recorded for F2 production following exposure to imidacloprid. No other measures for hormesis were statistically significant, but other trends of hormetic response were consistently observed. CONCLUSIONS: Given that variable distribution and degradation of insecticides in the field would result in a wide range of concentrations over time and space, these laboratory experiments suggest that exposure to sublethal concentrations of imidacloprid and azadirachtin could stimulate reproduction in M. persicae.