There are many species of coccinellids and a big number of these are predators of other insects. In these species, both the larvae and the adults are predators, feeding on aphids, mites, whiteflies, small insects, insect eggs, etc.
There are also a number of coccinellids that feed on plants. For example Epilachna spp. feed on plants and can sometimes become pests in eggplant or other crops.
Description and life cycle
Adult coccinellids are small beetles, round to oval in shape. Many species have black spots on red, orange or yellow forewings. Different species have a different color or a different pattern of markings and they range in length from about 1 mm to over 10 mm. Females on average are larger than males.
Many coccinellids prefer to feed on aphids, but when no aphids are available they will switch to other prey. Also cannibalism of eggs, larvae and pupae is common, especially when prey is scarce.
Adult females lay 200 to more than 1000 eggs in a few months time. Often they are deposited in small groups together. The number depends on the availability of food. If more prey is available they will lay more eggs, which allows them to keep up with the size of the pest population. Usually they will deposit their eggs on leaves and stems of the plant near prey, such as a colony of aphids. The eggs are small (about 1mm), cream, yellow or orange in color.
The larvae are very mobile and can travel big distances in search of prey. They don’t resemble the adults, but look a bit like an alligator with 3 pairs of legs. Larvae are usually dark with variable color markings depending on the species and in some species they are protected by waxy secretions. Usually there are 4 larval instars.
The last larval instar pupates attached to a leaf or other surface. Pupae are dark or yellow-orange in color and are not protected by a cocoon. Before pupating, larvae often wander some distance from the feeding sites to avoid the risk of cannibalism. The pupal stage lasts 3 to 12 days, depending on the species and the temperature.
Adults live several months up to a year. Ladybirds can have several generations each year.
Both adults and larvae are voracious feeders. During its development through four instars, the larvae will eat between 200 and 300 aphids. An adult may eat up to 50 aphids per day. Especially when pest populations are high they are very effective as predators, but when populations are low they are considered less effective. Depending on the type of crop there may be some crop damage before lady beetles have an impact on the pest population.
Because of their ability to survive on different types of prey or on pollen when there are not so many aphids present, lady beetles are very valuable.
Lady beetles can be mass-reared for use against aphids or other pests. The Department of Agricultural Extension (DOAE) in Thailand has developed rearing facilities and makes lady beetles available to farmers for field releases.
Lady beetles and most other natural enemies are easily killed by broad-spectrum pesticides. Therefore use of these pesticides should be avoided as much as possible.
Lady beetles benefit from shelter for protection from adverse weather conditions and for refuge when crops are harvested. This shelter could be provided by having some other plants around the field.