Determination, distribution, and environmental fate of Bacillus thuringiensis spores in various honeybee matrices after field application as plant protection product

Abstract

The increasing use of Bacillus thuringiensis (Bt)–based plant protection products (PPPs) has recently raised some concerns regarding their environmental accumulation and possible chronic exposure of non-target species, including pollinators, to higher than expected doses. The exposure level of such microbial PPPs in bee’s matrices under field conditions has not yet been described. Therefore, the current study aims at evaluating the realistic exposure level and comparing the distributions and persistence of Bt spores under field conditions. A field trial with spray application in oilseed rape (Brassica napus) as a representative bee-attractive crop was conducted. During the experimental period, different matrices, including honeybee-collected and -stored matrices as well as bee larvae and dead bees, were collected and analyzed using newly established methods. The concentration of Bt spores in the various matrices was quantified. The results show high levels of Bt spores in honey sac and pollen pellets with reduction over time but no reduction of Bt spores in the stored matrices within the colony, i.e., nectar and bee bread, over time. Our results show for the first time the exposure level of bees to Bt spores under realistic field conditions and are fundamentally important for assessing potential exposure and risks for pollinators.

Bacillus thuringiensisbioinsecticide influencesDrosophilaoviposition decision

“…[80,83] Very recently, doses close to 10 8 CFU/g have been measured in honey bee matrices and flowers after the field application of the maximum recommended Bt bioinsecticide dose and concentrations up to 10 7 CFU/g still persisted two days after application. [84] Expression of behavioural avoidance toward Btk bioinsecticide was observed with the regular suspension, as well as with the dialyzed suspension and each of its fractions independently. This excludes a role in the avoidance of small molecular weight compounds of the formulation, [85] , and suggests that of spores, toxins, or residual bacterial fragments.…”

“…[80,83] Very recently, doses close to 10 8 CFU/g have been measured in honey bee matrices and flowers after the field application of the maximum recommended Bt bioinsecticide dose and concentrations up to 10 7 CFU/g still persisted two days after application. [84]…”

Purified cytosolic crystals from Bacillus thuringiensis as a novel active pharmaceutical ingredient (API)

“…There are also increasing environmental concerns with using live spores, e . g ., Bt spore accumulation in non-target beneficial insects (25). For these and other reasons, using live Bt spore crystal lysates would be challenging from a regulatory and therapeutic vantage point as ingested anthelmintics ( e .…”

“…As such, in some places there are limits in terms of acceptable residual levels of Bt spores on foods sold (23,24). There are also increasing environmental concerns with using live spores, e.g., Bt spore accumulation in non-target beneficial insects (25). For these and other reasons, using live Bt spore crystal lysates would be challenging from a regulatory and therapeutic vantage point as ingested anthelmintics (e.g., oral cures for intestinal nematodes) (14).…”

Efficient and Scalable Process to Produce Novel and Highly Bioactive Purified Cytosolic Crystals from Bacillus thuringiensis

“…As such, in some places such as Europe, there are limits in terms of acceptable residual levels of Bt spores on foods sold ( 23 , 24 ). There are also increasing environmental concerns with using live spores, e.g., Bt spore accumulation in nontarget beneficial insects ( 25 ). For these and other reasons, using live Bt spore crystal lysates would be challenging from regulatory and therapeutic vantage points as ingested anthelmintics (e.g., oral cures for intestinal nematodes) ( 14 ).…”