Farm scale management of natural enemy resources and the effect on insect biological control across a semi natural habitat gradient

Abstract

Agricultural land use and its disruption of natural landscapes threatens the provision of ecosystem services, such as biological control by natural enemies because of habitat simplification and management intensification. The notion that surrounding non-crop habitat may improve biological control of crop pests by beneficial natural enemies (eg., predators and parasitoids) has emerged as a paradigm for conservation biocontrol. However most studies that evaluate the effect of local management practices rarely identify and include other important predictors such as landscape compositional values of habitat which can have great repercussions for nectar provision. We here study the effect of in-farm flower strip use on the control of aphids in a semi natural habitat (SNH) gradient. The mean number of aphids per plant varied among farms, with significantly more aphids on farms without flower strips. The % SNH negatively affected the mean number of aphids per farm. The proportion of parasitized aphids per plant was significantly affected by the landscape predictor as well as the treatment, with greater mummification rates with flowers and greater % SNH. Predators did not respond to either the treatment or the % of SNH surrounding the farms. Flower strips of faba beans and buckwheat in the field positively affected Diaeretiella rapae, as has been shown before laboratory studies, being independent of the landscape context here considered, and could be an important management strategy to decrease Brevicoryne brassicae in brassica crops in the field.