Aphids to thin out by end of week

Smokey-winged ash aphids congregate, lay eggs this time of year


Entomologist Richard Zack explains that the concentration of aphids on campus will thin out by the end of the week.

LINH NGUYEN, Evergreen reporter

Swarming about, and into the faces of those on campus, are masses of aphids searching for a place to lay their eggs.

These smokey-winged ash aphids are what WSU entomology professor Richard Zack calls a pest.

“They don’t cause any problems, they don’t bite or do anything like that,” he said. “They’re not a damaging species.”

This means that these particular aphids are not harmful to plants or humans, Zack said, but rather a minor inconvenience for those walking around campus.

Zack said the smoky-winged ash aphids are one of 4,000 species of aphids, with this specific type of aphid located in the inland Northwest.

“Aphids are basically small little insect bags that feed on plant sap,” Zack said. “They stick their mouth parts down into a plant and suck the sap out.”

Zack said they are a “two-host” insect — they inhabit and lay eggs in two different locations, or in this case, trees.

The aphids survive as wingless creatures in the summer and feed underground at the roots of conifer trees, Zack said.

“In the fall, [the aphids] actually produce a generation of aphids that has wings,” Zack said.

This is when most people are seeing the aphids, as the females leave conifer trees to find a new host: ash trees.

The female aphids do so by flying in groups to ensure safety from predators such as ladybugs and birds, before safely laying their eggs on their second host.

“So in the summer, the conifers are the host,” Zack said. “And then in the winter, the ash is the host.”

However, the majority of the aphids never end up finding a host, and generally die before doing so, Zack said. The lifetime of these aphids is roughly 10 days to two weeks.

Once the new generation of aphids hatches in the spring, the process reoccurs, Zack said, as a wingless set of aphids will feed at the roots of the ash trees before developing a winged generation to fly back to conifer trees before the beginning of summer.

Due to the cooling fall temperatures, the aphids around Pullman will likely disappear by the end of the week, Zack said.

“This is probably going to be the end of them,” he said.