Simple Summary
In this study, the impact of dinotefuran (DF) administered via pollen paste to a bee colony damaged by Varroa mites was investigated. Seasonal changes in the number of adult bees (those capped brood) and the mite-prevalence among adult bees were measured through a field experiment over 180 days. It was found that the bee colony collapsed under the intake of a smaller amount of DF due to the synergistic effect of DF and mite-damage. Because the daily pesticide-free sugar-syrup intake per bee in the DF-exposed colony administered via pollen paste was greater than that of the control colony, DF may have an appetite-promoting effect. Since the consumption of DF-containing pollen paste per bee per day showed almost no difference between all colonies, DF seems to have no repellent effect. Mite-prevalence continued to rise and became almost 100% near the time of colony extinction. The inner-temperature-fluctuation-range of the hive-box (Ti) was smaller than that of the ambient temperature (Ta). The inner-temperature-fluctuation-range of the DF-exposed-colony hive-box was larger than that of the control-colony hive-box. If Ta was 30oC or less, Ti became higher than Ta; if Ta was 30o C or more, Ti became lower than Ta.
Abstract
Neonicotinoids, such as dinotefuran (DF), have caused a variety of problems, such as massive loss and winter failure of bee colonies as the price for reducing farm work, as such neonicotinoids continue to maintain high insecticide activity over a long period of time. In this study, a field experiment was conducted over about six months to investigate the effects of DF on bee colonies damaged by Varroa mites. This study examined the long-term changes in the sizes of bee colonies, the intake of sugar syrup (SS), the intake of pollen paste (PP) (which is a vehicle for administering DF), the intake of DF,the mite-prevalence of bees, and the inside and outside temperatures of the hive-boxes. The variation width of the inner temperature of the hive-box was less than that of the ambient temperature (Ta). The inner temperature of the hive-box was adjusted to about 30oC of Ta as the boundary. If Ta was lower than 30oC, the inner temperature of the box was higher than Ta, and if Ta was higher than 30oC, the inner temperature was lower than Ta. The temperature variation width of the DF-exposed colony was greater than that of the control colony. The average intake of SS per bee per day in the DF-exposed colony was greater than that of the control colony. The average intake of PP per bee per day in the DF-exposed colony was almost equal to that of the control colony. These results suggest that bees do not avoid DF and ingest PP without making a distinction between toxic and pesticide-free PP. In the period from the start of DF administration to colony extinction, the intake of DF per colony was about 865 μg/colony, the intake per bee was 14 ng/bee, and the intake per bee per day was less than 0.1 ng/bee/day. These intakes are much lower than the previous ones recorded (60–65 ng/bee, 0.27–2.32 ng/ bee/day). These discrepancies may be because attacks from mites and Japanese giant hornets hastened the colony’s collapse. Seasonal changes in the mite-prevalence of honeybees were approximately the same regardless of the bee colonies. At the end of August (the start of the attacks by Japanese giant hornets), the mite-prevalence increased rapidly. Even if the number of bees damaged by mites decreased, the mite-prevalence continued to increase, approaching 100% before the bee colonies became extinct. In this study, it was found that bee colonies collapse via the intake of a smaller amount of DF due to the synergistic effect of DF and mite-damage. To prevent a bee colony collapse, beyond minimizing the adverse effects to a bee colony from neonicotinoids such as DF with long-term residual effects and high insecticide properties, it is necessary to reduce the damage from mites as much as possible while considering the synergistically adverse effects of neonicotinoids and miticides.
Author(s): Toshiro Yamada