Support biological control of aphids by supporting spiders and carabids in cereal fields

Chemical control of pests is a vital tool in conventional crop production, but the time when insecticides solved all problems with pests seems to be over; Many old insecticides lose their effect when pests develop resistance to them, some particularly environmentally harmful agents can no longer be used in the EU and few new agents enter the market. New approaches to pest problems are therefore desirable.

In organic farming, preventive measures such as good crop rotations and resistant varieties, are the main ways to prevent or mitigate attacks by diseases and pests. There is also an effort to utilize the ecosystem's natural control of pests, by various ways of supporting natural enemies of pests. In order to preserve and promote such biological control on arable land, however, there is a need for a better understanding of how the attacks of pests are influenced by the diversity of natural enemies, such as ground beetles and spiders, and of their prey.

In her doctoral thesis at SLU, Eve Roubinet first made an analysis of what the scientific literature says about this issue. This showed that a greater diversity of predatory arthropods increases the biological control of plant-eating insects.

In order to be able to promote important natural enemies it is important to know more about the relationship between the predators and their prey, i.e. what the food chains look like, and what this means for biological control. In the second part of her thesis Eve Roubinet examined the stomach contents of predators using a newly developed DNA technology, and she was thereby able to show what the predators ate during different parts of the season.

The focus was on ground beetles and spiders that have broad diets (generalists) and who eat aphids in cereal fields. The studies showed that these predators are important natural enemies of aphids, and that they have very broad diets consisting of herbivores, soil fauna and other predators.

"My thesis highlights the importance of understanding the entire food web to be able to better design conservation biological control strategies in agricultural fields", says Eve Roubinet.

It is not only important to focus on the insect pests and their natural enemy species, but also on their predation on alternative prey.

Eve Roubinet also shows that the contribution to biological control by individual species of generalist predators differs during the cropping season and that the community of generalist predators might therefore be complementary in provisioning of biological control.

"It seems that a high diversity of predators provides a more stable biological control, over the whole season", says Eve Roubinet.

Diverse predator communities could be supported by reduced-input crop management, and by practices that support abundant alternative resources for generalist predators over the entire year.

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MSc Eve Roubinet, department of ecology defended her thesis Food webs in agroecosystems – implications for biological control of insect pests at SLU in Uppsala on April 1, 2016. The opponent was Associate Professor Mary Gardiner, The Ohio State University, Wooster, OH, USA.

More information

Eve Roubinet 018-67 23 12, Eve.Roubinet@slu.se

Link to the thesis (pdf)
http://pub.epsilon.slu.se/13146/

Press images (may be published without charge in articles about these findings, please acknowledge the photographer).

• Predator-prey food web in early and late season in a barley field. Fore moe details, see p. 48 in the thesis.
• Pterostichus melanarius - a carabid with aphids in its diet. Photo: Mattias Jonsson