Biological control of pests can take many forms and be influenced by farmers in different ways. In greenhouses, gardeners can add beneficial organisms, such as Aphidius colemani, a parasite that attacks aphids. In the field, introductions of beneficial organisms are far less effective. The insects often disperse quickly and will only reproduce if they have the appropriate habitat.
German scientists investigated a few ways farmers can reap the benefits of natural pest control by providing habitat for the creatures that attack pests. Certain types of birds, spiders, wasps, flies and beetles and other insects can help farmers by preying upon or parasitizing pests.
The researchers compared aphid numbers on wheat fields adjacent to “semi-natural habitat,” such as meadows, hedgerows and uncultivated areas, to fields on farms with several other types of crops. All of the farms were non-organic.
The scientists were surprised to find that crop diversity appeared to play a greater role in natural pest control than the inclusion of semi-natural habitat. The author states that the “study indicates that at least three functional crop groups (not crop species per se) ought to be cultivated to increase biological control.” That means growing three types of grain or even three types of vegetables won’t necessary have a great effect. They considered separate “crop groups” to include cereals (grain), one- to two-year fallows, sunflowers, other flowers, short-term grass crops, legumes, corn, canola, root crops, other vegetables and industrial crops.
The researchers demonstrated that “crop diversity augments natural enemies and biological control. On small scales below 500 m, an increase from one to three dominating crop types enhanced [biological control of insects] by up to 33 per cent.”
— Janet Wallace
Source: Sarah Redlich, Emily A. Martin and Ingolf Steffan-Dewenter. Landscape- level crop diversity benefits biological pest control. Journal of Applied Ecology. March. 2018.