Photo by Joseph Berger, Bugwood.org
The European earwig (Forficula auricularia) has been in the United States for more than a century, thriving in all but the far southeastern states. The omnivorous arthropod has been noted as both a pest and as a beneficial insect, feeding on crops as well as on aphids.
Recently, researchers have found evidence that suggests it also damages citrus groves, both in Europe and the United States. The European earwig has fed on very young, emerging citrus fruit in California, causing fruit scarring, but it’s not known how extensive this damage is. To get an idea, researchers at the University of California, Davis looked at the behavior of earwigs in citrus orchards in California’s Central Valley. Their results, which include a new, farmer-friendly method of collecting earwig samples, were published in February in the Journal of Economic Entomology.
Now-retired entomology professor Jay Rosenheim led the researchers. They found that earwigs begin feeding on budding citrus fruit much earlier in the growing season than expected. However, the density of earwigs seemed to bear no relationship to fruit damage. They determined that the earwigs traveled up and down the trunks of citrus trees during early fruiting season, well before flower petals began falling.
TRAP TESTING
To begin, the researchers had to develop an easy and relatively cheap sampling method. After considering four methods, they found that small wooden boards (costing less than $2 each) were effective as traps for the nocturnal earwigs. Testing 27 such boards, which were laid flat on the ground at the edge of a tree canopy, the researchers found the board traps had many more earwigs per trap than the other methods. The researchers applied a sticky barrier around the tree trunk or no barrier (as a control). They then used the boards to sample insect movements in 93 commercial citrus blocks over two years.
The sticky barriers were effective at halting earwig movement into citrus trees, but only if applied early enough in the season. Other researchers had found that the barriers resulted in a 50% reduction in fruit damage.
MORE RESEARCH NEEDED
The researchers also were trying to develop an estimate of economic damage caused by earwigs. “The economic impact is hard to pin down, because when we see damage, we don’t know if it’s generated by earwigs or by other early-season pests that also chew on tiny fruits — in particular, the fork-tailed bush katydids,” Rosenheim said.
The reasons behind earwig movements in citrus trees, where the insects climb up and down during feeding, are still a bit of a puzzle. “We still don’t fully understand what all that movement was about,” Rosenheim says.
The fact that the team could not find any relationship between earwig population densities and fruit damage underscores the need for more research on the biology of this insect.
Source: Entomology Today
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