Colorado State University Entomologist Predicts Low Numbers for Miller Moths, Increases in Aphids

It will be a below-normal year for miller moths and several species of insects, according to a Colorado State University expert. However, entomologist Whitney Cranshaw is predicting a sharp increase in aphid populations.

Cranshaw, professor in the Department of Bioagricultural Sciences and Pest Management, said low numbers for miller moths are the result of fewer of the caterpillar stage, known as the army cutworm, present last year and fewer eggs likely laid in the fall. Another contributing factor was wet weather during the spring months.

“With all the moisture early this year, there are abundant flowering native plants that will provide an abundance of nectar sources for the moths; they will not aggregate around landscape plantings as occurs in drought years,” Cranshaw said. “Flights will be later than normal and below normal in total number of miller moths. They will continue to dribble through town on their annual trek from the plains to the mountains.”

Decreased numbers for several other insect species are occurring this year. Cranshaw said the numbers of yellowjackets are down due to the cold, wet spring. Honey bees were off to a rough start largely because fall cold snaps cut off winter provisioning and the late spring delayed bloom, causing many colonies to starve. Clover mites, which primarily impact lawns, were way down this spring, according to Cranshaw, due to adequate moisture during the winter months.

However, where moisture has been abundant this spring, populations of aphids, small sap-sucking insects that feast on new growth on various trees, shrubs and flowers, have benefitted from the cool wet spring, according to Cranshaw.

“There has been a sharp uptick in aphids on woody plants and ornamentals in the past week. Furthermore, I’m not seeing a lot of predator activity – lady beetles, lacewings and syrphid flies – so I suspect that the next couple of weeks we will see aphids spiking, then crashing when predators finally catch up and the succulent new growth ceases,” said Cranshaw.

Cranshaw notes the aphid situation is much different in more arid portions of Colorado, especially the southeastern part of the state which has been particularly dry.