Learning impairment in honey bees caused by agricultural spray adjuvants

Open Access
Ciarlo, Timothy Joseph
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 10, 2011
Committee Members:
  • Christopher Albert Mullin, Thesis Advisor
  • associative learning
  • proboscis extension reflex
  • organosilicone
  • adjuvant
  • colony collapse disorder
Spray adjuvants are often applied to crops in conjunction with agricultural pesticides in order to boost the efficacy of the active ingredient(s). The adjuvants themselves are largely assumed to be biologically inert and are therefore subject to minimal scrutiny and toxicological testing by regulatory agencies. Honey bees are exposed to a wide array of pesticides as they conduct normal foraging operations, meaning that they are likely exposed to spray adjuvants as well. It was previously unknown whether these agrochemicals have any deleterious effects on honey bee behavior. The proboscis extension reflex (PER) assay was used to measure the olfactory learning ability of honey bees treated orally with sublethal doses of the most widely used spray adjuvants on almonds in the Central Valley of California. Olfactory learning is important for foraging honey bees because it allows them to exploit the most productive floral resources in an area at any given time. Any impairment of this learning ability may have serious implications for foraging efficiency at the colony level. Several of the most widely used adjuvants from each of three different adjuvant classes (nonionic surfactants, crop oil concentrates, and organosilicone surfactants) were investigated in this study. Learning was impaired after ingestion of 20 µg organosilicone surfactant, indicating harmful effects on honey bees caused by agrochemicals previously believed to be innocuous. Organosilicones were more active than the nonionic adjuvants, while the crop oil concentrates were inactive. Ingestion was required for the tested adjuvant to have an effect on learning, as exposure via antennal contact only induced no level of impairment. A decrease in percent conditioned response after ingestion of organosilicone surfactants, which has been demonstrated here for the first time, may be an indication of severe, colony-level impacts. Organosilicone spray adjuvants may therefore play a vital role in the ongoing losses that characterize Colony Collapse Disorder (CCD).