The effectiveness of releasing natural enemies to combat crop pests depends on the landscape surrounding the field, new US research suggests.
Augmentative biocontrol is an emerging strategy for sustainable growers – and popular because it negates the need for expensive and potentially harmful insecticides.
However, a study by a team from Cornell University highlights some of the complexities.
When they released natural predators into crops surrounded by forests and natural areas, it led to fewer pests, less plant damage and increased crop biomass.
However, the results were reversed in crops on farms surrounded by other farms. Despite added predators, there were more pests, more plant damage and reduced crop biomass.
“Landscape composition influences how predator species interact with one another and thereby mediates the potential consequences for biological pest control,” says lead author, Ricardo Perez-Alvarez.
The results of the study, which focused on cabbage crops and cabbage pests, are published in the journal Nature Scientific Reports.
Perez-Alvarez and colleagues set up cabbage plots across 11 farms in central New York, with surrounding natural environments ranging from farms to natural areas and forests.
Each farm had two plots. The first was left alone, exposed to the naturally occurring predators. In the other, they introduced predators such as soldier bugs (Podisus maculiventris) and ladybugs (Coccinellidae).
They then collected a range of data that included surveys of pest and predator abundances, plant damage and final crop yields. They also conducted lab experiments to better understand the relationships between predators and how those interactions impact pest control.
The reasons behind their results are complex, they say, and dependent upon the interactions between local predators and those that are added, which can vary on a case-by-case basis.
However, they do suggest that the amount of food available in complex habitats, such as forests, may be important in providing natural predators with alternative food sources.
At the same time, simple landscapes, such as farms, could increase antagonistic interactions among natural predators, which compete for food.
The researchers acknowledge that their results are system-dependent and the specifics arising from other enemy-pest systems can create idiosyncrasies that demand case-by-case consideration.
However, it’s a start.
“Ultimately, a greater understanding of landscape-moderated interactions between pests and their natural enemies would provide much needed information for pest management practitioners with respect to how and where natural enemy augmentation can be implemented more effectively,” the researchers write.
Amelia Nichele is a science journalist at The Royal Institution of Australia.
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