Trying to improve biocontrol methods to protect the cabbage industry in the US state of New York, worth about $ 60 million a year, scientists came to an interesting conclusion.
When cabbage moth larvae flood the field, modern vegetable growers often try to control pests by releasing a large number of natural pest enemies, such as ladybugs, to avoid costly and potentially environmentally harmful insecticides. However, agrarians sometimes see mixed results.
In a new study by experts at Cornell University of the cabbage industry in the US state of New York, scientists were able to find out that the effectiveness of using natural enemies to control pests depends on the landscape surrounding the field.
“The landscape context can provide information on how best to use this strategy in the field,” says Ricardo Perez-Alvarez, co-author of “The effectiveness of enhancing biological control depends on the landscape context,” published in Scientific Reports.
Scientific work has shown that the production of entomophages leads to a decrease in the number of pests, better plant protection and an increase in the biomass of crops on farms surrounded by more forest and natural areas and fewer agricultural land.
But on farms, mostly surrounded by other farms, there was a reverse picture: despite the release of entomophages, the number of pests did not decrease.
The causes of this phenomenon are complex and depend on a combination of different factors, including the interaction between local entomophages and those that are added.
“Landscaping also affects how predatory insect species interact with each other,” writes Perez-Alvarez.
The scientific work was focused on the cultivation of cabbage, pests of the culture (cabbage whitewash and cabbage moth) and entomophages.
In central New York, 156 native species of predatory insects, including seven parasitoid wasps, prey on these cabbage pests.
Among the entomophages, there are two “universal soldiers” that are popular in biocontrol: a predatory bug from the Podisus maculiventris family of bugs and a ladybug. Usually they complement each other well, because bedbugs feed on larvae, and ladybugs feed on eggs of cabbage butterflies and moths.
In the course of the study, scientists set up experimental plots on 11 cabbage farms in the center of the state, which represented a number of surrounding landscapes from agricultural land to natural areas.
On each farm, two plots were allocated for cabbage: one in the field with the natural number of entomophages, and the second with the addition of an additional number of predatory bugs and ladybugs.
Then scientists collected a wide range of data on the number of pests and predators, plant damage, and total yield. They also conducted laboratory experiments to better understand the relationships between predators and how these interactions affect pest control.
According to the results of the experiments, scientists came to the conclusion that the results of biocontrol vary in each case and largely depend on the interaction between local predators and those that are added to the environment.
It can be assumed that the amount of food available on farms surrounded by natural landscapes, such as forests, is important for providing natural predators with alternative food sources. At the same time, agricultural landscapes, such as farms, can enhance the antagonistic interactions between natural predators, as they have to compete for food.
Ultimately, a deeper understanding of the interactions between pests and their natural enemies, governed by the landscape itself, will give pest control practitioners much-needed information about where and how natural increase in enemy numbers can be implemented more efficiently, the researchers write. ...
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