Lady Beetles

Another key pest target for predatory insect is the Colorado potato beetle. One of the most ferocious eater of the potato beetle is a cute looking and docile predatory insect the lady(bird) beetle. Lady beetles are readily available commercially in North America and I'm sure throughout the world as well. They are heavily used by the garden industry and by organic growers. Many insecticides especially those used for the Colorado potato beetle are harmful to the predators especially those that feed on aphids such as the green lacewings outlined in last June's column.

Lady Beetles are commercially available BUT the species commonly sold (Hippodamia convergens) is not the preferred lady beetle for effective bio-control of pests. There are over 400 species of lady beetles in North America. The one sold is the convergent lady beetle that is captured while overwintering in migratory hordes, many in California. These beetles are captured and shipped while in a dormant state (diapause) and it takes about a month before they will lay eggs. Also, they tend to disperse away from the field in which they were placed. Improved techniques in pre-feeding lady beetles prior to release has improved egg maturation and earlier deposit. Several sources now sell these "pre-conditioned" beetles but are ten-fold more expensive. It is still recommended to release them only in large fields.

I found a couple of sources, in Indiana and Quebec, of one of the best species of lady beetle, Coleomegilla maculata (pink spotted lady beetle). This species is a particularly voracious egg predator of Colorado potato beetle. They're dark pink to red with lots of large black spots, and are often found in or near alfalfa and grain (esp. Wheat) fields. Populations build up in these fields in late spring and summer. Both adults and larvae eat eggs, and the larvae will eat C. potato beetle larvae, green peach aphid nymphs and adults, and European corn borer eggs. The adults will also feed on nectar, pollen and GPA honeydew.

The seven-spotted lady beetle (Coccinella septempunctata) is another species which is voracious C. potato beetle and green peach aphid predator. It was introduced into the USA from Europe and is found throughout North America. This 7-black spotted orange lady beetle appears in potato fields everywhere and is the best known of the predators. Although not yet commercially available, this species has recently been mass reared.

Life Cycle -- Lady beetles overwinter as adults in debris, fallen leaves, building cracks, under rocks, and in mulch. Some migrate for winter covering at high altitudes as much as 9,000 ft. These include C. maculata (pink spotted), C. septempunctata (seven-spotted) and H. convergens (convergent) lady beetles. During overwintering, they go through a dormant or inactive period as adults called diapause. In spring, as weather warms, they break diapause and become active. Adults resume feeding and begin egg production in crops, especially alfalfa and winter wheat in Nebraska. They will move into potato fields looking for Colorado potato beetle eggs and green peach aphid nymphs. In these fields and near prey, eggs are deposited. Eggs hatch after 3-7 days and the first generation of larvae are eating by the end of May. Although the adult is most recognized as a predator, the larvae are voracious eaters of C. potato beetle eggs and aphid nymphs. Each larva can consume 500 to 1000 green peach aphids during its 2-4 weeks of growth. Pupae are formed in the dining area and, after 5-7 days, the adult emerges to eat and lay eggs. There are 2-5 generations per season and a life cycle lasts about a month.

Appearance -- There are hundreds of species of lady beetles in North America alone. Most are beneficial to potato production eating many insect pests. The two most voracious and common are Coleomegilla maculata (pink spotted) and Coccinella septempunctata (seven-spotted). The adult of the pink spotted ladybeetle's body is oblong and the wing covers are deep pink to red with 12 large black irregular spots that may converge. The seven-spotted ladybeetle adult is round-oval and domed; its wing covers are orange with seven circular black spots. Adults are about ¼ inch long and are found from April to late September. A female will lay 200-1000 eggs. Eggs are spindle-shaped or oblong, yellow to orange-red, and clustered (less than 20) on leaf surfaces. They are usually found near prey, aphids and C. potato beetle. The eggs look similar to C. potato beetle eggs but these are larger, darker red-orange, and are more clustered, 30-50 eggs. Colorado potato beetle eggs are only found on solanaceous plants such as potato and nightshades while ladybeetle eggs will be found there and in other crops (alfalfa, wheat) and weeds, wherever prey is nearby. The ladybeetle larvae are elongated and dark with a slightly pointed rear. Their legs stick out from the side as if they are bow-legged. Their color is gray to black and have spotting of yellow, orange or blue. The pupae are round and hang for the leaf surface attached in the rear. They are dark usually with spots.

Pesticide tolerance by lady beetles to insecticides has not been demonstrated.