Effect of wheat-based intercropping systems on pests and natural enemies: a review with a special focus on China

Intercropping is a farming practice consisting of cultivating at least two plant species simultaneously in the same field, but without necessarily sowing and/or harvesting them at the same time. By increasing plant diversity at the field scale, intercropping may be an efficient method to control insect pests and support natural enemies on the associated crops.
We performed a systematic research of the peer-reviewed literature which studied the effect of intercropping systems on pests and natural enemies, compared to pure stands. The research was restricted to wheat-based systems, as it is an important crop worldwide, and the main one in Northern China.
A total of fifty research papers were obtained from the literature search. Results from a vote-counting analysis, using binomial tests, indicated that pest abundance was significantly reduced in intercropping systems compared with pure stands, but their natural enemies were not particularly favoured (i.e., predators and parasitoids). Among these papers, 23 were studies from China. There, wheat was associated with cotton in relay-intercropping, as well as alfalfa, chili peppers, fava bean, garlic, mung bean, oilseed rape and pea in strip-cropping. Aphids were systematically reduced and natural enemies (i.e., predators and parasitoids) significantly favoured in intercropping systems compared to pure stands.
This study shows that intercropping is a viable practice to biologically control pests, and potentially support natural enemies, especially in China. Therefore it can be seen as a viable method to reduce insecticide use in wheat production systems.