MEXICAN BEAN BEETLE

A, leaves skeletonized by bean beetle feeding. a, Egg cluster; b, larva; c, pupa with larval skin still attached; d, adult. (All about twice natural size.)

MEXICAN BEAN BEETLE

Mexican bean beetles overwinter in the adult or beetle stage, usually in woodlands near bean fields. They leave their winter quarters in the spring, and the female beetles lay their eggs on the under side of the bean leaves. These eggs hatch in 5 to 14 days into larvae that feed principally on the under side of the bean leaves. The larvae grow rapidly, passing through four stages. Each stage is larger than the preceding one. They reach full growth in 20 to 35 days. The full-grown larva attaches itself to the under surface of the leaf on which it has been feeding or to some nearby plant or object, and changes to the pupa, or inactive stage. After 10 days or so the adult beetle emerges from the pupa. Within 2 weeks the female beetle is ready to deposit eggs for another brood.

Control: Spray or dust with derris, cube, or cryolite. Any of the following insecticides applied to the beans so as to cover the under side of the leaves thoroughly will protect the plants. (Spraying has given better results than dusting.)

To prepare a derris or cube spray, use finely ground derris or cube root (4 percent rotenone content) at the rate of one-half ounce (3 level tablespoonfuls) to 1 gallon of water; or 1 1/2 pounds to 50 gallons.

To prepare a cryolite spray, use 1 ounce (3 level tablespoonfuls) of cryolite to 1 gallon of water; or 3 pounds to 50 gallons. To prepare a derris or cube dust, containing 0.5 percent of rotenone, use 10 ounces of finely ground derris or cube root (4 percent rotenone content) to 4 pounds 6 ounces of diluent (finely ground talc, clay, sulfur, tobacco, gypsum, or other powder, except lime); or 12 1/2 pounds to 87 1/2 pounds of the diluent.

To prepare a cryolite dust, use 3 pounds of cryolite to 2 pounds of diluent (finely ground talc or sulfur); or 60 pounds of cryolite to 40 pounds of the diluent. cryolite should not be applied to beans after the pods begin to form.

The first application of insecticide (spray or dust) should be made when Mexican bean beetles are found in the field when eggs become numerous on the under side of the leaves. Repeat every week or 10 days if the insects are numerous.