Blister Beetle
(Spicauta spp.), Meliodae, COLEOPTERA


DESCRIPTION (several species)

Adult - Blister beetles are slender insects 12 to 19 mm long. They have prominent heads and may be black, gray with black spots, or black and yellow striped. Color plate.

Egg - The yellow, cylindrical eggs are 1.3 to 1.8 mm long.

Larva - Each of the seven larval instars differs in size, shape and color. They can be 2.5 to 13 mm long, slender to plump, and white to yellow or brown. All instars have 3 short pairs of ventral legs and 12 body segments, excluding the head.

Pupa - The white, 10 mm-long pupae darken gradually beginning with the eyes.


BIOLOGY

Distribution - Blister beetles are found throughout the continental United States and the agricultural areas of Canada. Although fairly common in North Carolina, they are not often important pests.

Host Plants - Blister beetles have a wide host range. Some economically important agricultural hosts include alfalfa, sweet clover, soybean, potato, tomato, melon, cotton, and eggplant.

Life History - Blister beetles have an unusual life cycle. They usually overwinter as sixth instar larvae 2.5 to 4 cm deep in the soil. In the spring, resting larvae molt into active, nonfeeding larvae which soon pupate. Adult blister beetles begin to emerge in June. Adults can be found well into September but are most abundant in July. During the summer months, they congregate and feed voraciously on foliage or flowers (depending upon the particular species). Two to three weeks after mating, each female deposits up to six egg masses in the soil. These masses may contain 50 to 300 eggs each. Active larvae hatch from the eggs 1-1/2 to 3 weeks later and search for grasshopper egg cases. A few days after locating and feeding on the eggs, the active larvae molt and become fairly inactive. The grubs continue to feed and molt until they are fat, almost legless, fifth instars. These larvae create oval, hibernating chambers in the soil, molt into sixth instars, and overwinter. Development usually continues the following spring but the larvae may remain inactive for as long as two years. Sometimes the fifth instar larvae molt directly into the pupal stage, bypassing the last two larval instars. As a general rule, however, blister beetles complete one generation each year.


CONTROL

Control of blister beetles in soybeans is seldom necessary. Only when foliage loss exceeds 35 percent prebloom or 15 percent postbloom are controls justified. Spot applications are usually adequate to divert loss. For control recommendations, consult the current North Carolina Agricultural Chemical Manual.