Intercropping oilseed rape with wheat and releasing Harmonia axyridis sex pheromone in Northern China failed to attract and support natural enemies of aphids

Abstract

Description of the subject. Increasing plant diversity with flowering plants and releasing semiochemicals did not attract and support natural enemies of insect pests for biological control. Objectives. We tested the effect of intercropping oilseed rape with wheat, and releasing the sex pheromone of the ladybeetle Harmonia axyridis, on the abundance of aphids’ natural enemies. Method. Four treatments repeated three times were compared in an experimental field in Langfang (Hebei, China): (i) oilseed rape–wheat intercropping + sex pheromone release, (ii) oilseed rape–wheat intercropping solely, (iii) pure-stand wheat and (iv) pure-stand oilseed rape. Ladybeetles, hoverflies, lacewings and parasitoids were pan-trapped during nine weeks in spring 2016 in each treatment. Results. A diversity of natural enemy species was trapped. However, intercropping and the release of the sex pheromone did not significantly increase their abundance compared to pure-stands. Conclusions. The results are discussed in regard to technical issues to improve the experimental protocol for future research in China.