Insects Are Optimistic With This Warm Spring ...

Insects are coming to life throughout Missouri, and I am noticing the emergence of a native tree defoliator, the eastern tent caterpillar. Tent caterpillars build their tightly webbed tents in the crotch of various trees and shrubs, with their favorites being fruit trees such as wild cherry, plum, apple, and crabapple. They also feed on ornamental trees such as ash, birch, maple, oak and poplar. These insects rest during the day within the tent, and crawl out of the tent at night to chew on leaves and possibly developing fruit.

Aphids are one of the most common insects that can attack home, garden and landscape plants

As each caterpillar leaves the nest, it will spin a strand of silk as it travels, and it is assumed this helps the caterpillar find its way back to the nest. Tent caterpillars over-winter in shiny brown egg masses glued to twigs, and eggs usually emerge at about the same time as tree buds begin to break open. When abundant, tent caterpillars can destroy a substantial number of leaves, and can weaken a tree. Tent caterpillars are usually kept under control by natural enemies, which typically prevent tent caterpillar outbreaks from persisting long enough to cause serious damage. Tent caterpillar larvae and nests can easily be dislodged from trees and destroyed using a broom or heavy water spray. Once caterpillars are knocked off the tree or out of the nest, they usually cannot get back onto the tree and fall easy prey to ground feeding birds such as robins. If tent caterpillars are persistent from year to year, egg masses can be pruned out of the limbs in the fall, which reduces insect numbers the subsequent year.

The elevated temperatures this spring have also promoted an early emergence of aphids. Aphids, sometimes called plant lice, are one of the most common insects that can attack home, garden and landscape plants. They tend to cluster on the new growth of roses, perennials and other plants. Aphids are small, softbodied insects, usually 1/8 inch or less in size, with long legs and antennae; they are usually wingless and their color can vary from green, pink, yellow, tan, gray, white or black. The aphids that I am currently seeing in high numbers in my yard are covered with a white powderlike coating that from a distance, appear to have a covering of mold or white spray paint.

When aphid numbers are high, plants are stressed and therefore less vigorous

Aphids have an extremely high rate of reproduction, which enables insect numbers to build up very rapidly. When aphid numbers are high, plants are stressed and therefore less vigorous. Aphids damage the plant by piercing the leaves, stems and flowers and sucking sap and other fluids, weakening plants and leaving them discolored and stunted. Foliage may look puckered or distorted. Aphids tend to congregate on new plant growth in the early spring and curled, distorted leaves are usually a good indicator that aphids are present. Lush plant growth is very attractive to aphids and it has been noted that high nitrogen fertilizer rates can increase aphid reproduction.

Aphids have many natural enemies that successfully attack them and provide very effective control. They are a favorite diet for ladybird beetles, which eat entire aphids. One ladybird beetle can eat up to 100 aphids per day.

Parasitic wasps are very successful in attacking aphids. The wasp stings the aphid and in doing so, deposits her egg inside the aphid’s body. The wasp egg then hatches into a larva that grows and consumes the aphid’s internal body. The larva pupates inside the aphid and emerges as an adult wasp through a small exit hole it chews through the aphid’s outer skin. After the wasp emerges, the aphid’s corpse is referred to as a mummy. Aphid mummies are a good indicator that parasitic wasps are at work in the garden.

Other predators include lacewings, syrphid flies and assassin bugs. Encourage natural enemies of aphids by using synthetic insecticides as little as possible. Before treating any plants, thoroughly inspect the plant for the presence of natural enemies.

Aphids can be knocked off the plants with a strong jet spray of water. Insecticidal soaps or horticultural oils also work well to control aphids. It is best to not apply insecticidal soups or horticultural oils in direct sunlight as they can have phytotoxic effects on the plant. Heavy aphid infestations can be difficult to control if aphids hunker down in the folds of leaves, flower buds or new growth. Aphid colonies can be reduced by pruning and disposing of aphid infested plant material, and can also be controlled by squishing with fingers.

For more information on web producing insects, refer to MU Extension Guide G7271 ( http://muextension.missouri.edu/xplor/agguides/pests/g07271.htm ), and for information on aphid control, see MU publication M145, Controlling Tree and Shrub Pests, or MU Guide G7274, Aphids, Scales and Mites on Garden and Landscape Plants.

Mary Kroening Dept. of Horticulture 573-882-9633