This project seeks to elucidate the multiple pathways by which wild bees may be impacted by neonicotinoid pesticide residues in soils that are used for nesting material. While significant progress has been made with regards to our understanding of the impact of neonicotinoid pesticides on honeybees and dietary exposure to residue in pollen and water, little is known about other exposure pathways which may exist for wild bees which use a variety of materials beyond pollen and nectar to complete their life cycles. Use of mud by mason bees (Osmia spp.) is thought to be a potential source of exposure to pesticide residue which has not been examined. This project represents the first attempt to look at nesting materials as a potential exposure pathway for mason bees to neonicotinoid pesticides.
Objective 1: To determine how adult female mason bee nest establishment is affected by imidacloprid soil drench treatments when treated mud is used for nesting.
Objective 2: To determine how offspring which develop within nests with treated soil are affected, in terms of survivorship and sublethal effects such as size, weight, and sex ratio.
Objective 3: To determine if female mason bees will detect or choose soils with lower residual concentrations of neonicotinoid.
Eleven hundred Osmia lignaria (eastern subspecies) adult cocoons were obtained from a commercial source (Mason Bee Company, Deweyville, UT) in February 2019 and have been kept in cold storage at 4◦ Celsius until ready for emergence. Three hundred cocoons were emerged in the laboratory between March 11 and March 14, which included 120 females and 180 males. The females were individually marked and treated with contact exposure to soil for one hour in petri dishes at four different concentrations (< 1, 50, 500 and 1000 parts per billion (ppb)), then released into six 20 x 20 x 7 foot flight cages each enclosing 5 to 6 flowering blueberry bushes at Durham horticulture research farm in Watkinsville, Georgia. Each tent contains a Styrofoam nest block with 36 nesting holes filled with paper tubes. Five females at each treatment level were released in each tent, for a total of 20 females per tent, and 30 untreated males were released per tent. Males were not treated in order to isolate the effects to females which contact the soil regularly for nest building. Bees were released in the flight cages on March 20, 2019 and behavior is being observed daily for 20 minutes per cage to ascertain effects on nesting behavior, including nest recognition, mud collection, pollen collection, and nest building progress. When nesting is completed, nest tubes will be removed and examined with an otoscope to determine number of cells in each tube, then incubated in the lab for the remainder of the spring and summer. In fall, cocoons will be extracted from the paper tubes, weighed, measured, and examined for holes (indicating potential parasitism). The following spring, adults will be emerged, counted, sexed, measured, and weighed. In addition, twenty blueberry racemes were tagged in each tent, terminal buds were counted and marked on the tag, and additional twenty racemes were tagged on blueberry bushes adjacent to each tent to assess fruit set. Blueberries on marked racemes will be counted, harvested, weighed and dissected to determine seed set.
Another group of 180 adult male and female O. lignaria were exposed to treated soil in petri dishes at the same four concentrations (< 1, 50, 500 and 1000 ppb) and released into twelve insect dorms [24 x 12 x12 inches] on March 25th, 2019. Seven females and eight males were released each dorm, and mortality is being assessed daily and will continue for ten days. This experiment will be repeated two more times, and a subset of these individuals will be dissected to determine effects on ovary and testes development.
To determine effects on larval development, 25 reeds filled with O. lignaria larval instars were obtained on March 27th from a professional bee producer in Florida. A total of 200 larvae have been grafted onto eight 24-well plates. Four well plates contain pollen injected with various concentrations of imidacloprid (0, 10, 50, 100, 500, 1000, 3000 and 5000 ppb in solution, 10 μl of the solution injected into each pollen ball), and four well plates contain soil treated at the same levels as above (< 1, 50, 500 and 1000 ppb). This method will isolate the effects of treated soil used for nesting material vs. dietary exposure, and will also give us an LD50 for larval dietary exposure to pollen. Another set of 25 reeds are expected later in April and the experiment will be repeated. Endpoints assessed will include mortality, development/growth including time at each instar, cocoon size/ weight (initial), successful emergence in the following spring, size and weight of adults, egg maturation of females (oocyte development after pollen meal or juvenile hormone (JH) exposure), and testes development of males after emergence.
A laboratory choice experiment will also occur in April, 2019. For this experiment, mated and fed four-day-old females will be placed in choice arenas in the following soil treatments: choice of 0 and 50, 0 and 500, 0 and 1000, 50 and 500, 50 and 1000, 500 and 1000 ppb, with a full spectrum light source over the choice arena. Thirty females per treatment will be observed in choice chambers and time spent in each choice chamber will be logged.
Data obtained All treated soil and pollen will be sent to Dr. Anthony Lagalante, professor of chemistry at Villanova University for residue analysis to confirm the treatment levels.
Data from the above studies will be used to create an agent based model and risk assessment, and subsequent development of best management practices
All experiments are currently running and thus results have not yet been assessed.
Educational & Outreach Activities
I have developed a curriculum to teach groups how to recognize, promote, and keep wild bees, including mason bees, leafcutter bees and bumble bees, and have conducted outreach to the following groups:
· Gwinett County Beekeepers Association, August 2018 – approximately 35 beekeepers
· Lee Arrendale State Prison, beekeeping class, September 2018 – approximately 15 inmates
· Tri-county Beekeepers Association, October 2018 – approximately 20 beekeepers
· Northeast Georgia Mountain Beekeepers Association, Jan 10, 2019 – approximately 30 beekeepers
Guest Lecturer, Athens Academy High School Honors and AP Biology classes, April 2019 – approximately 120 students
Trees Atlanta, ‘trees for bees’ workshop, July 2019 – number of attendees tbd