The specific responses of Acari community to Bt cotton cultivation in agricultural soils in northern China

Transgenic cotton expressing the Bacillus thuringiensis (Bt) insecticidal crystal (Cry1A) protein effectively controls the cotton bollworm and thus has been planted extensively in China. However, the large-scale release of Bt cotton may have undesirable effects on soil fauna due to Bt protein accumulation and the pleiotropic effects of genetic manipulation. A survey of soil mites was carried out monthly for two consecutive years (2009–2010) in Bt and non-Bt cotton fields. The soil mites were extracted using modified Tullgren funnels and were identified to the genus level, when possible. The results suggested that the effects of Bt cotton on soil mite community size were time dependent and taxonomic group specific. The cumulated abundance over a year was always higher in non-Bt fields for Oribatida; this effect was statistically significant in 2010 for Prostigmata and Astigmata. The changes in the community variables tested were similar between Bt and non-Bt cotton fields in 2009, whereas the taxonomic group richness, Shannon–Weaver index and evenness index were significantly different between Bt and non-Bt cotton fields in 2010. Additionally, sharp inter-annual fluctuations in the community composition of the soil mites were found, accompanied with the replacement of some taxonomic groups. Finally, the dominances of some taxonomic groups were significantly different between Bt and non-Bt cotton fields. Bt cotton cultivation fostered Laelapidae populations while inhibited Tectocepheus abundance in 2009. However, Bt cotton cultivation negatively impacted the abundances of Scheloribates and Nothrus in 2010. In conclusion, Bt cotton cultivation exerted specific impacts on soil mites.

► We analyzed the community size, diversity indices and composition of soil mites in Bt and non-Bt cotton fields.
► The impacts of Bt cotton on soil mites are taxonomic group specific.
► Pronounced adverse impacts of Bt cotton on soil mites occurred in October and lasted to May the next year.
► The taxonomic group richness (S), Shannon–Wiener index (H′) and evenness index (J) can demonstrate community composition of soil mites.
► Sharp inter-annual fluctuations in the community composition of the soil mites were found, accompanied with the replacement of some taxonomic groups.