Compliance with recommended Varroa destructor treatment regimens improves the survival of honey bee colonies over winter.

The ectoparasitic mite Varroa destructor affects honey bee colony health and survival negatively, thus compelling beekeepers to treat their colonies every year. A broadly used mite control regimen is based on two organic molecules: formic and oxalic acids. To ensure optimal efficiency, several applications of these acids at pre-defined time points are recommended. These recommendations are mainly based on experiments conducted under controlled conditions. Studies evaluating the effectiveness under natural field conditions are lacking. We enrolled 30 beekeepers in a longitudinal study in three cantons in Switzerland and monitored the management and health of their colonies for two years. We assessed compliance with mite control recommendations and measured V. destructor infestation rates, indexes of colony productivity (brood size and honey harvest), and colony mortality in 300 colonies. We observed a 10-fold increased risk of colony death when beekeepers deviated slightly from the recommended treatment regimen compared to compliant beekeepers (odds ratio: 11.9, 95% CI: 2.6-55.2, p = 0.002). The risk of colony death increased 25-fold in apiaries with substantial deviations from the recommendations (odds ratio: 50.4, 95% CI: 9.7-262.5, p < 0.0001). The deviations led to increased levels of V. destructor infestation ahead of wintering, which was likely responsible for colony mortality. After communicating the apparent link between low compliance and poor colony survival at the end of the first year to the beekeepers, we observed better compliance and colony survival in the second year. Our results highlight the positive impact of compliance with the recommended V. destructor treatment regimen on the health of honeybee colonies and the need to better communicate the consequences of deviating from the recommendations to improve compliance. Compliance also occasionally decreased, which hints at concept implementation constraints that could be identified and possibly addressed in detail with the help of social sciences to further promote honey bee health.

Impact of nutritional stress on the honeybee colony health.

Honeybees Apis mellifera are important pollinators of wild plants and commercial crops. For more than a decade, high percentages of honeybee colony losses have been reported worldwide. Nutritional stress due to habitat depletion, infection by different pests and pathogens and pesticide exposure has been proposed as the major causes. In this study we analyzed how nutritional stress affects colony strength and health. Two groups of colonies were set in a Eucalyptus grandis plantation at the beginning of the flowering period (autumn), replicating a natural scenario with a nutritionally poor food source. While both groups of colonies had access to the pollen available in this plantation, one was supplemented with a polyfloral pollen patty during the entire flowering period. In the short-term, colonies under nutritional stress (which consumed mainly E. grandis pollen) showed higher infection level with Nosema spp. and lower brood and adult bee population, compared to supplemented colonies. On the other hand, these supplemented colonies showed higher infection level with RNA viruses although infection levels were low compared to countries were viral infections have negative impacts. Nutritional stress also had long-term colony effects, because bee population did not recover in spring, as in supplemented colonies did. In conclusion, nutritional stress and Nosema spp. infection had a severe impact on colony strength with consequences in both short and long-term.

Elucidating the mechanisms underlying the beneficial health effects of dietary pollen on honey bees (Apis mellifera) infested by Varroa mite ectoparasites.

Parasites and pathogens of the honey bee (Apis mellifera) are key factors underlying colony losses, which are threatening the beekeeping industry and agriculture as a whole. To control the spread and development of pathogen infections within the colony, honey bees use plant resins with antibiotic activity, but little is known about the properties of other substances, that are mainly used as a foodstuff, for controlling possible diseases both at the individual and colony level. In this study, we tested the hypothesis that pollen is beneficial for honey bees challenged with the parasitic mite Varroa destructor associated to the Deformed Wing Virus. First, we studied the effects of pollen on the survival of infested bees, under laboratory and field conditions, and observed that a pollen rich diet can compensate the deleterious effects of mite parasitization. Subsequently, we characterized the pollen compounds responsible for the observed positive effects. Finally, based on the results of a transcriptomic analysis of parasitized bees fed with pollen or not, we developed a comprehensive framework for interpreting the observed effects of pollen on honey bee health, which incorporates the possible effects on cuticle integrity, energetic metabolism and immune response.

The glass is not yet half empty: agitation but not Varroa treatment causes cognitive bias in honey bees.

Honey bees (Apis mellifera) are prone to judge an ambiguous stimulus negatively if they had been agitated through shaking which simulates a predator attack. Such a cognitive bias has been suggested to reflect an internal emotional state analogous to humans who judge more pessimistically when they do not feel well. In order to test cognitive bias experimentally, an animal is conditioned to respond to two different stimuli, where one is punished while the other is rewarded. Subsequently a third, ambiguous stimulus is presented and it is measured whether the subject responds as if it expects a reward or a punishment. Generally, it is assumed that negative experiences lower future expectations, rendering the animals more pessimistic. Here we tested whether a most likely negatively experienced formic acid treatment against the parasitic mite Varroa destructor also affects future expectations of honey bees. We applied an olfactory learning paradigm (i.e., conditioned proboscis extension response) using two odorants and blends of these odorants as the ambiguous stimuli. Unlike agitating honey bees, exposure to formic acid did not significantly change the response to the ambiguous stimuli in comparison with untreated bees. Overall evidence suggests that the commonest treatment against one of the most harmful bee pests has no detrimental effects on cognitive bias in honey bees.

Neonicotinoid-Coated Zea mays Seeds Indirectly Affect Honeybee Performance and Pathogen Susceptibility in Field Trials.

Thirty-two honeybee (Apis mellifera) colonies were studied in order to detect and measure potential in vivo effects of neonicotinoid pesticides used in cornfields (Zea mays spp) on honeybee health. Honeybee colonies were randomly split on four different agricultural cornfield areas located near Quebec City, Canada. Two locations contained cornfields treated with a seed-coated systemic neonicotinoid insecticide while the two others were organic cornfields used as control treatments. Hives were extensively monitored for their performance and health traits over a period of two years. Honeybee viruses (brood queen cell virus BQCV, deformed wing virus DWV, and Israeli acute paralysis virus IAPV) and the brain specific expression of a biomarker of host physiological stress, the Acetylcholinesterase gene AChE, were investigated using RT-qPCR. Liquid chromatography-mass spectrometry (LC-MS) was performed to detect pesticide residues in adult bees, honey, pollen, and corn flowers collected from the studied hives in each location. In addition, general hive conditions were assessed by monitoring colony weight and brood development. Neonicotinoids were only identified in corn flowers at low concentrations. However, honeybee colonies located in neonicotinoid treated cornfields expressed significantly higher pathogen infection than those located in untreated cornfields. AChE levels showed elevated levels among honeybees that collected corn pollen from treated fields. Positive correlations were recorded between pathogens and the treated locations. Our data suggests that neonicotinoids indirectly weaken honeybee health by inducing physiological stress and increasing pathogen loads.

Age-related changes in the behavioural response of honeybees to Apiguard®, a thymol-based treatment used to control the mite Varroa destructor.

The parasitic mite Varroa destructor is responsible for heavy losses in honey bee colonies and represents a major threat to the beekeeping industry. Essential oils offer an attractive alternative to the use of synthetic chemicals for the control of varroa. Amongst them, thymol appears to be particularly promising. However, treatments using thymol as their active substance, such as the gel formulation Apiguard(®), are suspected to have adverse effects on honey bee colonies. In this study, laboratory assays are used to investigate the effects of Apiguard(®) exposure on honey bee behaviour. Our results reveal that honey bee responses to this anti-varroa treatment change with honey bee age. While 2-day-old bees respond neutrally to Apiguard(®), older bees generally avoid the Apiguard(®) gel. Responses of forager bees were particularly striking. Foragers appear to be repelled by Apiguard(®). Touching their antennae with Apiguard(®) induces robust fanning behaviour. Our data suggest, however, that forager bees exposed to Apiguard(®) in the hive can become habituated to this treatment. These results offer interesting new perspectives on the effects of Apiguard(®) on honey bee behaviour and serve to highlight age-related changes in honey bee responses to gustatory, as well as olfactory cues.