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

Abdulrahim T Alkassab,Martina Janke,Jens Pistorius,Hannes Beims

doi:10.1007/s11356-022-19414-5

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.

Highlights

Nowadays, the growing world population requires constant high crop yields
The commercial formulations based on different isolates of Bacillus thuringiensis (Bt) subsp. kurstaki (Btk) and Bt subsp. aizawai (Bta) to control lepidopteran larvae are the most sprayed bioinsecticides in organic and conventional farming (Bravo et al 2011)
The current study aims at (1) evaluating the realistic exposure level under field conditions after spray application in oilseed rape as a representative bee-attractive crop and (2) comparing the distributions and persistence of Bt spores in different bee-collected and -stored matrices

Summary

Introduction

The growing world population requires constant high crop yields. To avoid losses caused by weeds, pests, and diseases, which can reach 37% of all potential crops (Pimentel 1997), farmers follow several approaches. Integrated pest management (IPM) is a general approach, including chemical plant protection products (PPPs) to suppress pest populations below the economic threshold (Peshin et al 2009). Aizawai (Bta) to control lepidopteran larvae are the most sprayed bioinsecticides in organic and conventional farming (Bravo et al 2011). These products are recommended to be sprayed repeatedly within a short interval (3–8 days) due to the sensitivity of toxin crystals or spores to abiotic conditions like UV (EFSA Biohaz Panel (EFSA Panel on Biological Hazards), 2016). The formulations contain different compounds to protect spores and toxin crystals (Brar et al 2006). Previous studies reported that Btk can persist on the leaves’ surface over 72 h after application, decreasing within 28 days to the environmental background level (Bizzarri and Bishop, 2008; Raymond et al 2010)

Methods

Results

Conclusion