Pollen Exposed to Aerial Pesticide Spray Is a Major Exposure Pathway for Stingless Bees

Area of Science:

• Ecology
• Environmental Science
• Toxicology

Background:

• Assessing pesticide exposure routes is crucial for pollinator risk assessment.
• Bacillus thuringiensis israelensis (Bti) is used in Australian mosquito control, applied aerially to coastal habitats.
• Pesticide exposure pathways for stingless bees in these environments are not well understood.

Purpose of the Study:

• To investigate the foraging behavior of stingless bees and their exposure to Bti in coastal mosquito habitats.
• To identify potential exposure routes and quantify Bti presence in bees and their collected resources.
• To develop a Bti detection method for experimental manipulation of insecticide exposure pathways.

Main Methods:

• Sentinel hives of Tetragonula carbonaria were placed in Bti-treated areas.
• Pollen DNA metabarcoding (ITS2) assessed foraging behavior.
• Bti-specific qPCR quantified Bti in pollen loads, hive stores, and bee bodies.

Main Results:

• Stingless bee foragers primarily visited Avicennia marina (grey mangrove) flowers early in the study.
• Bti was detected in 27% of pollen samples and 4% of adult bees.
• Contaminated A. marina pollen was identified as the primary Bti exposure route.

Conclusions:

• The study identified contaminated mangrove pollen as a significant exposure pathway for Bti in stingless bees.
• Detected Bti concentrations were low, likely posing minimal risk to the bees.
• The developed Bti qPCR assay can be used to further investigate insecticide exposure mechanisms in stingless bees.