Some of the pesticides commonly used by UK growers on pear and apple orchards are harmful to earwigs, which are now known to be natural predators of several top-fruit pests.
Professor Jerry Cross, a research leader at East Malling Research (EMR) in Kent, advised delegates at this year's British Independent Fruit Growers Association annual technical day (31 January) to try to avoid using pesticides that are harmful to earwigs.
Cross said a piece of research carried out by EMR on behalf of the Horticultural Development Company has tested the effects of a range of widely used pesticides on earwig populations.
It showed that some of the products being used by growers are actually reducing earwig numbers. "Equity, Tracer and Calypso were amongst the worst," he said.
Cross explained to delegates that one of the tests saw earwigs on leaves put in a laboratory environment and sprayed with pesticides made up of the same solution rate used in orchards.
"In these tests, chlopyrifos killed the lot," he said. Trials carried out in orchards as part of the same project had similar results.
"Data show that the spray programmes we applied were having adverse effects," Cross told the delegates. "But (our) earwig-friendly programmes allowed earwigs to build up through the season."
He pointed out that the test results were mixed to some extent because some products, including Coragen and Dipel DF, "are safe to use but a lot of the other products are obviously harmful".
Beneficial earwigs - Predators of pear suckers and woolly aphids
Professor Jerry Cross also told delegates that studies over the past decade in Europe and the UK have shown that pear sucker and woolly aphid numbers are insignificant in trees where earwigs are abundant.
He explained that earwigs are omnivores that eat both other insects and plants. "Many other pests, such as codling moths, are significantly reduced. But (earwigs are) very low or absent in a lot of orchards. The lack of earwigs is a contributory cause of several pest problems."
He continued: "There are large variations in earwig populations and the cause of this variation is unknown - (it could be) a lack of food or shelter, or exposure to pesticides.
"We need to look after earwigs. Once upon a time we considered them to be important pests. But they are (only) secondary pests on apples and pears. They enlarge existing holes in the fruit but we know that sound fruit is not attacked.
"However, they are (only) primary pests in peach and strawberry (crops)."