Abstract
Beekeepers providing pollination services for California almond orchards have reported observing dead or malformed brood during and immediately after almond bloom—effects that they attribute to pesticide exposure. The objective of this study was to test commonly used insecticides and fungicides during almond bloom on honey bee larval development in a laboratory bioassay. In vitro rearing of worker honey bee larvae was performed to test the effect of three insecticides (chlorantraniliprole, diflubenzuron, and methoxyfenozide) and three fungicides (propiconazole, iprodione, and a mixture of boscalid-pyraclostrobin), applied alone or in insecticide-fungicide combinations, on larval development. Young worker larvae were fed diets contaminated with active ingredients at concentration ratios simulating a tank-mix at the maximum label rate. Overall, larvae receiving insecticide and insecticide-fungicide combinations were less likely to survive to adulthood when compared to the control or fungicide-only treatments. The insecticide chlorantraniliprole increased larval mortality when combined with the fungicides propiconazole or iprodione, but not alone; the chlorantraniliprole-propiconazole combination was also found to be highly toxic to adult workers treated topically. Diflubenzuron generally increased larval mortality, but no synergistic effect was observed when combined with fungicides. Neither methoxyfenozide nor any methoxyfenozide-fungicide combination increased mortality. Exposure to insecticides applied during almond bloom has the potential to harm honey bees and this effect may, in certain instances, be more damaging when insecticides are applied in combination with fungicides.
Highlights
IntroductionAlmonds are highly dependent on insect pollination [1] and as a result, growers of California almonds rented 1.48 million colonies of honey bees in 2017 at a cost of over 253 million dollars [2]
The honey bee (Apis mellifera) is heavily relied upon by modern agriculture for pollination services.Almonds are highly dependent on insect pollination [1] and as a result, growers of California almonds rented 1.48 million colonies of honey bees in 2017 at a cost of over 253 million dollars [2]
This study investigates the effects of the sterol biosynthesis-inhibiting (SBI) fungicide propiconazole, as well as other fungicides commonly applied to almonds during bloom, including iprodione (Rovral) and the combination of pyraclostrobin and boscalid (Pristine), on the toxicity of the insecticides chlorantraniliprole, methoxyfenozide, and diflubenzuron to larval honey bees reared using an in vitro method [48]
Summary
Almonds are highly dependent on insect pollination [1] and as a result, growers of California almonds rented 1.48 million colonies of honey bees in 2017 at a cost of over 253 million dollars [2]. A number of honey bee colonies rented for almond pollination in California in 2014 were impacted by honey bee die-offs. 40% of colonies in almond orchards experienced adult honey bee deaths or dead and deformed brood, and 20% of colonies were completely dead [3]. Pesticide use data reported by the California Pesticide Information Portal (CALPIP) [4] indicates that a range of insecticides and fungicides are applied to almond orchards during the blooming period (Figure 1). Insecticides that do not carry label language prohibiting their application when bees are Insects 2019, 10, 20; doi:10.3390/insects10010020 www.mdpi.com/journal/insects
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