Mexican bean beetle

Eggs: Eggs are approximately 1.3 mm in length and 0.6 mm in width, and are pale yellow to orange-yellow in color. They are typically found in clusters of 40 to 75 on the undersides of bean leaves.
Larva: The newly-hatched larva is light yellow in color and not over 1.6 mm in length. The body is covered with rows of stout branched spines, arranged in six longitudinal rows on the backs. The spines at first are yellow, but later become darker at the tips and more conspicuous. The larva has a soft body that tapers posteriorly and has an anal segment having a sucker-like apparatus for attachment to feeding surfaces. The mature larva is from 6.0 to 9.5 mm in length, and greenish yellow. The larva molts four times during the time of development. A few hours after molting, the tips of the spines become darker, giving a general greenish or dirty yellow color. Larvae have a tendency to aggregate in considerable numbers for pupation.
Pupa: The larva, when mature, attaches itself by the posterior end of the body to the underside of leaves, stems, or pods of the bean plants and often to parts of nearby plants. In this position, the larva pupates. After attaching, the larval skin is pushed back from the thorax to the abdomen where it remains in a whitish, wrinkled mass. The black tips of the spines remain conspicuous on the cast skin. The pupa is yellow, spineless, and of about the size and shape of the adult.
Adult: The adult is oval in outline, and about 6 to 7 mm in length. The newly emerged adult is of a straw or cream-yellow color. Shortly after emergence, eight black spots of variable size appear on each wing cover, arranged in three longitudinal rows on each wing cover. The adults darken with age until they become an orange-brown with a bronze tinge, at which time the black spots are less conspicuous. The males are slightly smaller than the females. Males can be distinguished from females by having a small notch on the ventral side of the last abdominal segment.
Life Cycle. The adult beetles come out from where they have spent the winter months under brush or leaves, as soon as warm weather arrives. Some may, however, delay their appearance until mid-summer. In mid-May adults tend to search out snap and lima beans, but by late June they begin ovipositing in soybeans. After feeding on the tender young bean plants for one to two weeks, the females lay their eggs, each depositing 500 to 600 of them in batches of 40 to 75 on the underside of the foliage. The eggs are carefully attached at the end so that they all stand vertically. They hatch in a week during warm weather but may require at least two weeks under cooler conditions.
The larvae feed voraciously for two to five weeks, depending upon the temperature. When first hatched, they all feed together. If the leaf is somewhat dry, the first hatched may devour the remaining unhatched eggs. As they grow older, they still retain their gregarious habits but tend to split up into small, scattered groups. When pupating, the larva fastens the tip of the abdomen to a part of the plant and starts to wiggle out of the larval skin, not entirely shedding it but pushing it back until only the tip of the abdomen remains in the skin. The pupal stage lasts for five to ten days, but may drag out much longer in the cool weather of autumn. The adults are strong fliers and travel long distances hunting for new bean fields. The beetles overwinter in moist, protected places, remaining dormant until spring.