The herbicide glyphosate negatively affects midgut bacterial communities and survival of honey bee larvae reared in vitro

Glyphosate, the most heavily used herbicide in the world, targets a specific enzyme found in plants and in some microorganisms, including some bacteria found in bee guts. These bacteria perform a variety of roles in bee guts and can affect bee nutritional status and immune health. Because glyphosate may be collected by foraging bees in pollen, nectar, water, and dusts and brought back to the hive, the researchers set out to test effects of chronic glyphosate exposure on the gut microbiomes, survival, weight, and development rate of honey bee larvae.

Honey bee larvae were reared for 5 days in sterile 48-cell tissue culture plates. On days 3-5 of rearing, at least 16 robust larvae per replicate were assigned to treatment groups fed 0.8, 4, or 20 mg/L of glyphosate in solution, a negative control group, and a positive control consisting of 45 mg/L of the organophosphate insecticide dimethoate. The two lower glyphosate concentrations are within the range of glyphosate concentrations measured in nectar in field studies, with the 20 mg/L concentration selected to mimic direct exposure to a label rate application of glyphosate; this rate is much higher than expected for chronic dietary exposure to glyphosate.

Exposure to glyphosate affected some but not all of the measured endpoints for honey bee larvae, and only at some concentrations. Brood survival was significantly lower for individuals fed diet with 4 mg/L and 20 mg/L glyphosate than for ones fed the negative control diet, and larval weight was significantly lower in the 0.08 and 4 mg/L glyphosate treatments but not the 20 mg/L treatment group. Developmental rate did not differ among treatment groups. The midgut bacterial composition of newly emerged workers fed the 20 mg/L glyphosate diet (measured at the phylum and class level, not to species) differed significantly from other treatment groups. The authors could not distinguish gut bacterial communities between the lower concentration treatment groups.

Authors: 
Dai, P., Z. Yan, S. Ma, Y. Yang, Q. Wang, C. Hou, Y. Wu, Y. Liu, and Q. Diao
Journal: 
Journal of Agricultural and Food Chemistry
Year published: 
2018
DOI: 
10.1021/acs.jafc.8b02212