Cool wet weather affects insect populations
The cool, wet weather this spring and summer is responsible for a rapid growth of some pest insect populations and the decrease of others, explained Mary Roduner, SDSU Extension consumer horticulture field specialist. He talked about pests found in horticulture but ones that are also problems in field crops.
"The extra moisture, with cooler temperatures is encouraging lush green plant growth later in the season than is normal for many areas of the state. This lush growth is encouraging the rapid growth of some pest insects. While at the same time, the wet weather is decreasing other insect populations," Roduner said.
Due to their reproduction habits, the saturated soils and excessive moisture has been devastating to populations of pests like, grasshoppers, cutworms and spider mites. However, because of their feeding habits, for other pests like, aphids and plant bugs who are attracted to lush foliage, weather conditions have resulted in a population boom.
More about the pests & insects
Grasshoppers, family Orthoptera, are a pest that becomes a serious problem in hot, dry weather. However, because female hoppers lay their eggs in soil mainly during the fall months, Roduner said this year, when the soil is cool and water saturated coming out of the winter, eggs will develop fungal infections and rot before they hatch. The result is greatly reduced grasshopper populations.
"Young grasshopper nymphs are also very susceptible to fungal infections and will avoid areas that remain wet or have high humidity. There will always be a few but the numbers are not high enough to do serious damage," she said.
Cut worms, family Noctuidae. Cut worms are the caterpillars that cut tomato and pepper seedlings off at ground level during the night hours. "This year's weather will cause many overwintering larvae or pupa to drown. This can reduce the population for several years," Roduner said.
The adult moths are often referred to as "miller moths." In warm, dry years the numbers can be very large, causing incredible amounts of damage to field and garden crops. Control is difficult, Roduner explained, because the larvae spend the day below the ground and targeting sprays are rarely successful. For the home gardener, a paper collar around the new transplant will prevent the larvae from reaching the plant stem.
Spider mites, order Acari, are a hot dry weather pest. While not an insect, but a spider relative, spider mites cause so much damage that most people lump them with insect pests. Two main varieties are found in gardens. Red spider mites make dense, fine webbing on plants and will cover plants completely. Two-spotted spider mites do not make much webbing but are far more destructive to plants.