Once considered a mostly benign backyard insect or occasional pest in certain crops, the European earwig (Forficula auricularia) is now under scrutiny for its role in damaging citrus fruits in California’s orchards. The European earwig has been present in the United States for over a century, first recorded in the early 1900s. Since then, it has spread across most of the country, establishing strong populations in temperate zones, though it’s notably sparse in the far southeastern states. Originally introduced from Europe, this insect is an omnivore, feeding on a wide range of food sources including decaying plant material, soft-bodied insects like aphids, and tender crop tissues. 

In agricultural systems, the earwig’s role revolves around preying on pest insects and offering natural control benefits in crops like lettuce and stone fruits. On the other, it has been observed damaging young shoots, flowers, and fruits. Let’s read further to find some exciting findings on earwigs by notable experts. 

UC Davis Study Brings New Data 

The research, published in February in the Journal of Economic Entomology, was led by retired entomologist Dr. Jay Rosenheim, along with colleagues from the UC Davis Department of Entomology and Nematology. Their goal was to investigate whether earwigs are a significant contributor to early-season citrus damage, and to develop a simple, affordable method for monitoring their activity in commercial orchards.  

Over a two-year period, the team studied earwig behaviour in 93 commercial citrus blocks across California’s Central Valley, a region that produces a significant portion of the nation’s oranges, mandarins, and lemons. They found that earwigs begin feeding on citrus fruits much earlier in the season than previously expected, often before flower petals have even fallen from the trees. However, one of the most surprising findings was that the number of earwigs present did not directly correlate with fruit damage levels. In orchards with high earwig populations, damage varied significantly from block to block. This suggests that other factors, such as weather conditions, tree architecture, or fruit variety, may be influencing how much damage actually occurs. 

A Cheap and Effective Monitoring Method 

After testing four different methods, they found that flat wooden boards, each costing under $2, were the most effective at capturing earwigs. Placed under the tree canopy, the boards provided shelter during the day, allowing researchers to count and collect earwigs with ease. 

This low-cost sampling tool offers a practical solution for growers looking to track local earwig populations without investing in expensive monitoring systems. The boards proved more efficient than other traps commonly used in entomological fieldwork. 

Sticky Barriers  

In addition to sampling, the researchers also experimented with sticky barriers wrapped around tree trunks. These barriers were used to prevent earwigs from climbing up into the canopy to feed on the developing fruits. When applied early enough in the season, the barriers were highly effective at blocking insect movement, supporting findings from earlier studies that had shown a 50% reduction in fruit damage using this technique. 

Still, the movement of earwigs up and down tree trunks, and the triggers for such behaviour, remains somewhat of a mystery. “They’re clearly active in the trees before damage begins, but they don’t always cause visible harm,” Rosenheim explained. “It’s a behavioural puzzle we’re still trying to piece together.” 

Implications for Growers 

For citrus producers in California, this research offers both clarity and complexity. While earwigs can and do feed on citrus, their presence does not always equate to economic damage. Growers may need to take a more nuanced approach to earwig management, focusing on early season monitoring and non-chemical control measures like sticky barriers. 

References 

• The European Earwig Could Be a New Serious Citrus Pest
• The European earwig Forficula auricularia (Dermaptera: Forficulidae) in California citrus: a sampling method, population surveys, and description of earwig movement into the tree canopy 
• Kahl-et-al.-2022-Journal-of-Economic-Entomology.pdf 

Photo Credit: Shutterstock/Mehes Daniel