Amelia Litz, 2016

Humboldt State University

Developing an approach for testing systemic pesticides on solitary bees: Effects of sulfoxaflor on Megachile rotundata

Systemic pesticide application has proved effective against a wide range of pests as it persists in and is absorbed by plant tissues, including tissues developing after initial application. This poses a risk to non-target organisms that rely on pesticide-containing, non-target plant tissue, for food. Testing for systemic pesticide effects on pollinators primarily focuses on Apis mellifera, the honeybee, which differs from solitary nesting pollinators in a variety of important life history traits. Preliminary testing is generally performed in laboratory studies, which may not reflect the interacting ecosystem dynamics that could intensify sublethal effects related to pesticide exposure. Sulfoxaflor is a new systemic insecticide acting on the insect nervous system, similar to neonicotinoids. We performed experiments to determine any lethal or sublethal effects of sulfoxaflor on Megachile rotundata, the alfalfa leafcutter bee. After application of different levels of sulfoxaflor to caged plots, floral resources, larval survival and development, and adult survival were monitored and analyzed. Sulfoxaflor concentrations were found in larval provisions for two-three weeks after treatment application, depending on initial concentration. All adult females died in treatments using both the manufacturer’s maximum and minimum recommended doses within the first two days after treatment. Larval survival was inconclusive, as there were no larvae to observe for the first few days post application in the highest experiments due to adult mortality. An unexpected effect of Sulfoxaflor treatment was the lengthening of flowering duration in the highest treatments. While lengthened flowering times could enhance female productivity once levels are safe for adults, until the fatal level of sulfoxaflor for larvae is known the safety of sulfoxaflor during the first week after application is still undetermined.

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