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Can Plant Diversity Help Fight Insect Invasions?

The results of a new study could help farmers grow crops with fewer insecticides.

By Nathan Collins


(Photo: John Moore/Getty Images)

For farmers, insecticides have long been viewed as a necessity of the trade. After all, they need something to chase away all the aphids and such plaguing their plants. But a new study suggests there may be a better way to repel insects: growing more diverse crops.

Biodiversity has a number of important benefits, for wild plants, animals, and farms. Broadly speaking, more diverse ecosystems are more resilient. That’s partly because different plants and animals will respond differently to threats like disease, pests, or climate change, but also because if one plant or animal falls victim to such challenges, others will be there to fill the hole left behind, helping to prevent the entire system from collapsing. That’s especially important on farms, since decreasing biodiversity could ultimately threaten our food supply (not that that’s done much to reverse the trend toward growing single crops year after year).

In the midst of this trend, Michigan State University Assistant Professor of Entomology William Wetzel and his colleagues wondered what the loss of farmland biodiversity might do to plant-eating insects. If an insect needs to eat plants with a particular protein density but lives among a diverse group of crops, for example, then it will often get too little or too much protein and might have a harder time surviving.

Do insects see diminishing returns from increases in various plant traits?

More generally, Wetzel and his team point out, if insects get diminishing returns from an increase in a given plant trait—for example, if they get ever-less out of each additional unit of protein—then biodiversity poses an evolutionary challenge.

The question then boils down to this: Do insects see diminishing returns from increases in various plant traits? To investigate, the team reviewed 76 studies published between 1968 and 2014 that looked at the relationship between plant traits and herbivorous insects’ growth or survival.

The result: Most insects experienced diminishing returns from an uptick in the levels of a number of plant nutrients. Overall, that means plant biodiversity could be a fairly effective insect repellent.