Threecornered Alfalfa Hopper
Egg - The white, oblong-oval egg is 0.9 to 1.3 mm long. It is slightly larger at one end, that end having a rough surface.
Nymph - The straw-colored, wedge-shaped, and heavily spined nymph has white legs, antennae, eyes, and abdomen. The mature nymph is active and about 4.6 mm long.
Distribution - Threecornered alfalfa hoppers occur as far north as Canada, but they are an occasional or potential problem only in the southern United States and in northern Mexico. They are prevalent from southern California to North Carolina, usually in early soybean plantings.
Host Plants - Threecornered alfalfa hoppers prefer leguminous plants such as alfalfa, soybean, bean, cowpea, and sweet clover. Other plants occasionally infested include tomato, melon, wheat, barley, oat, Bermuda grass, and Johnson grass, as well as some trees and shrubs.
Damage - Threecornered alfalfa hoppers girdle stems by their feeding and egg-laying activities. Nymphs and adults weaken the lower stem by piercing it with their needle-like mouthparts and extracting plant juices. As a result, lodging and breaking usually occur weeks after attack. There is some evidence that if damage is randomly scattered and occurs before bloom, in an optimum stand, reduction of at least 25 percent may be necessary to reduce yields. Therefore, these pests rarely cause economic damage.
Life History - Threecornered alfalfa hoppers overwinter as eggs in plant tissues or as adults protected by clumps of grasses. Young nymphs from overwintering eggs and overwintered adults begin feeding on weedy plants along field borders in the spring. During May or June, they migrate to soybean seedlings. Females then deposit 30 to 40 eggs, singly, in host plant stems. Nymphs hatch from the eggs 2 to 6 weeks later. They feed for 3 to 10 weeks before fifth instar nymphs molt into adults. On the average, 50 days elapse between egg deposition and adult emergence. The adults are strong flyers and readily migrate to new fields. Although the biology of this pest has not been studied in North Carolina, there are probably at least two generations each year.
Damaging infestations of the threecornered alfalfa hopper can be avoided by destroying weedy borders around fields and by seeding a little more heavily. The first practice eliminates overwintering sites from which the bugs will migrate to soybeans. The second practice reduces the importance of the loss of a few plants.
For specific chemical control information, consult the current North Carolina Agricultural Chemical Manual.
