Late Spring Shifts Activities of Miller Moths and Other Insects

This year’s cool spring has put many insects off their normal track, causing them to show up late or cut their season short. Numbers of miller moths trekking across Colorado’s Eastern Plains and Front Range are up slightly from last year, according to Colorado State University entomologist Whitney Cranshaw. However, a cooler than normal spring slowed the growth of the caterpillar stage, known as the army cutworm, and cool nights later retarded the flights of the moths.     

"The migration of moths in many areas of eastern Colorado is peaking in July, which is later than it has been for at least two decades," Cranshaw said. "Because of this, they have largely missed the boat regarding the flowering plants that they seek while on their annual pilgrimage to the mountains, and they will linger little in yards and gardens. As a result, migration flights are moving rapidly through eastern Colorado on the way to summering sites in the mountains."

Miller moths aren’t the only insect impacted. Cranshaw said the surge of aphids, which feast on new growth on various trees, shrubs and flowers, has been about two weeks late in many places. "We are now seeing an increase in lady beetles and other insects that normally feed on aphids. Other yard and garden insects, such as wood borers and flea beetles, have also been late."

The cool spring has also hit some insects hard. Yellowjackets have not fared well. "The cool and often wet spring weather came at a critical time when the overwintered queens try to establish new colonies," Cranshaw said. The late start also will limit how large yellowjackets colonies will get by late summer, reducing nuisance problems with these common stinging insects. Other insects, such as boxelder bugs and squash bugs, also may get caught short with the late start unless fall weather is unusually mild.

However, spring weather has little effect on insects that migrate into the region from warmer areas to the south. Painted lady butterflies, which have been scarce for the past two years, moved into the state in early May on winds that pushed them from wintering grounds to the southwest. This year, tomatoes and potatoes are being colonized by the potato/tomato psyllid, a migrant from Texas and Mexico that was nearly absent for the past couple of seasons.

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