‘Trap-and-move’ biological control can make insect villains into heroes

Originally published on Farming Future Food.

Earwigs can be both pest and pest control — but a solution for growers might be simply to move them from where they are causing trouble to where they can prove beneficial.

Over two years, scientists in the US tested mass-trapping European earwigs (Forficula Auricularia) in stone fruit orchards, where they pose a problem through fruit damage, and releasing them in apple and pear orchards, where they are a predator of key pests. The traps consisted of corrugated cardboard strips rolled into cylinders and attached to trees, in which the insects shelter.

Simple solutions can be effective

They found that the release of hundreds of trapped earwigs in the apple and pear orchards significantly reduced numbers of the key pests, the woolly apple aphid (Eriosoma lanigerum) and pear psylla (Psylla pyri). The approach could also help restore populations of the predators in the orchards, where numbers can dwindle due to broad-spectrum pesticide use and soil tillage approaches, coupled with their slow rate of recolonisation when numbers drop.

However, while the benefits for apple and pear growers are clear, the researchers found that removing the insects from the stone fruit orchards through trapping did not bring a significant decrease in earwig abundance or a reduction in fruit damage.

“In other biological control efforts involving moving predators into pest outbreak areas…there is a concern about the ‘robbing Peter to pay Paul’ effect (i.e., moving the predator causes a new outbreak in the area where they are moved from). Sourcing earwigs from stone fruit would avoid this issue,” the scientists explained in the journal Insects.

Carrying out such an approach may be of particular benefit to orchards which are transitioning to organic production and struggling to control pests, they noted.

Successful role-shift

“Our study demonstrates that biocontrol practitioners can make a natural enemy out of a pest using a trap-and-move approach between crops,” they continued.

“Omnivorous and generalist predators have many advantages for biological control, such as feeding on alternative food when prey numbers are low, reducing their dispersal rate and facilitating establishment in the crop.”

Trapping earwigs where they prove a problem could fill a gap not served by commercial breeders due to a lack of demand outside orchard crops and earwigs producing just one generation a year. Despite this lack of supply, earwigs are widely sought by orchard managers, the researchers noted.

Earwigs are not the only omnivorous insect that may be suitable for a trap-and-move strategy, they added. The bug Campylomma verbasci could also be a potential candidate, given its reputation as a pest of apples but a predator of pear psylla.