Soil-dwelling Bacillus spp. affect aphid infestation of calabrese and natural enemy responses in a context-specific manner

1 Plant growth-promoting rhizobacteria in the genus Bacillus have been shown to reduce growth and increase parasitism of some aphids, but the generality of these interactions is unknown. All previous studies have taken place in temperate conditions.
2 We studied the effects of seed application of three Bacillus species, singly and in mixture, on three aphid pests and their natural enemies, on field-grown calabrese (green sprouting broccoli) in the subtropical climate of south west India.
3 All three bacteria reduced populations of Brevicoryne brassicae and Myzus persicae, but had no effect on numbers of Lipaphis erysimi. Chewing insects (flea beetles and diamond back moth larvae) were also unaffected by the treatments. However, parasitism rates of aphids were higher on plants treated with the bacteria.
4 We conclude that Bacillus spp. shape above ground interactions in a context-specific manner, directly via altered field infestations of some pests and indirectly via natural enemy responses.