Sensitivity to imidacloprid insecticide varies among some social and solitary bee species of agricultural value

Authors: Sampson, Blair; GREGORC, ALES - University Of Maribor, Slovenia; ALBURAKI, MOHAMED - University Of Southern Mississippi; Werle, Christopher; KARIM, SHAHID - University Of Southern Mississippi; Adamczyk, John; KNIGHT, PATRICIA - Mississippi State University

Submitted to: Mississippi Academy of Sciences Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/17/2023
Publication Date: 5/3/2023
Citation: Sampson, B.J., Gregorc, A., Alburaki, M., Werle, C.T., Karim, S., Adamczyk Jr, J.J., Knight, P. 2023. Sensitivity to imidacloprid insecticide varies among some social and solitary bee species of agricultural value. Mississippi Academy of Sciences Proceedings. https://doi.org/10.1371/journal.pone.0285167.
DOI: https://doi.org/10.1371/journal.pone.0285167

Interpretive Summary: Pollinator health risks from long-lasting neonicotinoid insecticides like imidacloprid has primarily focused on commercially managed, cavity-nesting bees in the genera Apis, Bombus, and Osmia. We expand these assessments to include 12 species of native and non-native crop pollinators of differing levels of body size, sociality, and floral specialization. Bees were collected throughout 2016 and 2017 from flowering blueberry, squash, pumpkin, sunflower and okra in south Mississippi, USA. Within 30–60 minutes of capture, bees were installed in bioassay cages made from transparent plastic cups and dark amber jars. Bees were fed via dental wicks saturated with 27% (1.25 M) sugar syrup containing a realistic range of sublethal concentrations of imidacloprid (0, 5, 20, or 100 ppb) that are often found in nectar. Bees displayed no visible tremors or convulsions except for a small sweat bee, Halictus ligatus, and only at 100ppb syrup. Imidacloprid shortened the captive longevities of the solitary bees. Tolerant bee species lived ~10 to 12 days in the bioassays and included two social and one solitary species: Halictus ligatus, Apis mellifera and Ptilothrix bombiformis (rose mallow bees), respectively. No other bee species tolerated imidacloprid as well as honey bees did, which exhibited no appreciable mortality and only modest paralysis across concentration. In contrast, native bees either lived shorter lives, experienced longer paralysis, or endured both. Overall, longevity decreased with concentration linearly for social bees and non-linearly for solitary species. The percentage of a bee’s captive lifespan spent paralyzed increased logarithmically with concentration for all species, although bumble bees suffered longest. Of greatest concern was comparable debilitation of agriculturally valuable solitary bees at both low and high sublethal rates of imidacloprid.

Technical Abstract: Bioassays using Apis and wild non-Apis species with differing natural histories tested the health effects of sublethal concentrations of imidacloprid on bee longevity and paralysis. Species were chosen for their high abundance and differences in sociality, floral specialization, age, and sex. Throughout the year, adult Apis mellifera and 11 species of wild bees were collected from flowering Vaccinium (blueberry), Cucurbita (squash and pumpkin), Helianthus (sunflower), and Abelmoschus (okra). In the laboratory, absorbent dental wicks presented bees with 0, 5, 20, and 100 ppb imidacloprid in 27% (1.25M) sucrose solution. Bees displayed no visible tremors, except for Halictis ligatus, which exhibited brief convulsions and only at 100 ppb imidacloprid. Imidacloprid shortened the lifespans of all tested solitary bees. Adults of H. ligatus, Apis mellifera, Bombus 2 spp., and Ptilothrix bombiformis lived the longest, ~10 to 12 days, which inferred susceptibility to imidacloprid can be independent of body size. Imidacloprid equally reduced lifespans of both sexes of bees, except in Ptilothrix bombiformis, a species with aggressive, territorial males whose longevity perhaps diminishes further with imidacloprid-induced stress. All bee species became paralyzed sooner with increasing concentration. Among the generalist (polylectic) social species tested, bumble bees were the most susceptible to paralysis. In conclusion, bee tolerance to imidacloprid based on mean longevity and paralysis rate was highest in Apis followed by Xenoglossa, Halictus, Trachusa, Ptilothrix, Melissodes 2 spp., Bombus 2spp., Habropoda, Svastra, and Peponapis. Higher sensitivities of solitary oligolectic bees to imidacloprid could diminish yields of crops that serve as these bees’ principal floral hosts.