Catching hope: Possible ally in fight against harmful fruit fly discovered in Asian giant hornet trap

Karla Salp
Communications

Leptopilina japonica
Photo credit: Warren H. L. Wong,
University of British Columbia, Canada 

The benefits of the Washington State Department of Agriculture’s Asian giant hornet program just keep coming. Not only did they find and eradicate the first Asian giant hornet nest this fall, but now entomologists have found a very promising sign in the hornet traps: the first-known detection of Leptopilina japonica in the United States.

Leptopilina japonica is a tiny parasitic wasp that kills spotted wing drosophila (SWD,) which has been causing extensive damage to fruit crops in Washington for both farmers and gardeners. The wasp larvae consume the inside of the SWD larvae, eventually killing the fly. This exciting find, made in collaboration with the Systematic Entomology Laboratory (ARS-USDA) in Washington, DC, may lead to the development of biological control programs to potentially help manage SWD.

The wasp was found in WSDA’s Asian giant hornet traps. Traps sometimes catch bugs that are not the target pest. In this case, the orange juice and cooking rice wine bait was evidently very attractive to SWD, capturing countless numbers of the detested pests in addition to the wasp that entomologists discovered.

Leptopilina japonica laying eggs
in SWD larvae in a raspberry
Photo credit: Warren H. L. Wong, 
University of British Columbia, Canada

Finding better ways to manage spotted wind drosophila has been a challenge for farmers and researchers alike. First found in California in 2008, it was discovered in Washington in 2009. Unlike most fruit flies that lay their eggs in overripe or damaged fruit, SWD will lay eggs very early in the ripening process and in undamaged fruit. This means that ripe fruit could have SWD larvae in it. So far the only successful defense against SWD has been to apply pesticides when they are detected; a biological control would be a welcome management tool.

While a first for the U.S., the wasp was also recently discovered in British Columbia in the fall of 2019. Further research indicated that it may have been in Canada as early as 2016.

WSDA’s entomology lab still has thousands of Asian giant hornet trap contents to examine, but once their work and analysis is complete, the data on what was found in the traps will be made publicly available.

Leptopilina japonica
Photo credit: Warren H. L. Wong, 
University of British Columbia, Canada