Making gypsy moth history in Washington

by Karla Salp
Communications

For WSDA entomologists, August has been an exciting month.

Trap with 14 male gypsy moths

On July 31, record numbers of gypsy moths started showing up in traps in the Graham/Puyallup area. From two traps with two moths each to a trap with 6 moths, then 8, then 14. In all, 37 male gypsy moths were caught in that area on a single day.

By comparison, we found 25 moths total during three months of trapping last year across the whole state.

But for the entomologists and trappers in our Pest Program, the high point was still to come.

An extraordinary find 

Female gypsy moths laying egg masses hidden by a shrub

Given the unusually high number of catches, our gypsy moth team went to inspect the area Aug. 1 to find the source of the moths. Ground zero turned out to be a tree and some bushes in a residential neighborhood, where, for the first time in the program’s 40-year existence, entomologists found live female gypsy moths, actively laying eggs.

The first two team members to arrive had only an empty food carton from Taco Bell, but they quickly put it to use collecting live females. Because European gypsy moth females don’t fly, they were relatively easy to pick up and contain. Male moths tried to fly off, but they were caught mid-air and didn’t get far.

Eventually, more team members arrived with better collection equipment. By the end of the day, 71 female moths were found, several male moths, numerous egg masses, viable pupae, empty pupal casings, shed caterpillar skins and lots of caterpillar frass (poop.)

On follow up visits, about 30 additional females were found, until the bushes were removed on Aug. 4. In total, approximately 100 female gypsy moths were collected.

Processing the material

Part of the collected specimens after being sorted by WSDA entomologists 

But the work wasn’t done. All the moths, pupae and other materials collected had to be brought back to WSDA’s labs to be frozen and sorted, with entomologists sifting through the materials to tally the number of moths. Potentially useful specimens will be used for displays taken to public education and outreach events. The rest will be destroyed to ensure no gypsy moths survive or escape.

An invasive species scavenger hunt

WSDA entomologist collects two more female gypsy moths

While finding live females in infested areas like New England is relatively easy because of their high numbers, that is not the case in Washington where the pest is not established. Because the females don’t fly, finding the one tree or bush where a new infestation is starting is extremely difficult. There are very few clues to point you to where a female gypsy moth may be hiding. So how did WSDA find the infestation this year?

High numbers of male gypsy moth catches alerted WSDA to the problem. The team was able to focus their search in the area of the highest catches. The team also looked for vegetation that showed damage from caterpillar feeding earlier this spring. But adding to the challenge, females aren’t always located on vegetation. They can lay their eggs anywhere – such as outdoor patio furniture, the underside of a brick on a house or inside an old tire, for example – so other surfaces had to be examined as well.

This just-emerged female's abdomen is full of eggs

In the end, it was skill and luck that resulted in the discovery of the live moths.

A trapper hung a trap on the tree that morning. By noon, three male moths were already trapped in it. Inspection of the tree showed it had extensive caterpillar feeding on the leaves. When the team member pulled back the bushes at the base of the tree, the infestation was discovered on the concealed base of the tree and within the bushes themselves.

It was a truly exceptional find.

The program works

WSDA inspects tree and removes infested bushes

One of the takeaways from this experience is confirmation that WSDA’s gypsy moth program is working.

Last year, two male moths were caught less than a mile from the Graham/Puyallup site where the females were found this month. Because of that catch, a high-density grid of 64 traps per square mile was established in the area. The grid enabled the team to target their search more effectively, which led to finding the actively reproducing population.

Trapping continues this year through September, by which time moths will no longer be flying. Because of the work that our gypsy moth program has been doing for decades, WSDA has prevented gypsy moths from becoming established in Washington for more than 40 years.

This discovery is another example of the great work the pest program does to protect our neighborhoods, farms and environment from potentially devastating invasive pests.