By Dr. Ayanava Majumdar
When searching for aphid control measures, turn to nature first. Numerous vendors sell beneficial insects via their websites along with offering plenty of useful information. For example, ARBICO Organics (Arizona), Orcon (California), Gardens Alive (Indiana), and Nature’s Control (Oregon) sell insect predators in large numbers and at least one vendor sells it as a “beneficial insect program” with weekly shipments adjusted to your pest control needs. Note that beneficial insects are slow acting in pest outbreak situations, so use beneficial insects preventively when pests are in low populations and have not overwhelmed the crops you are trying to protect. Follow the release instructions that come with the products, and modify your spray schedule to adjust for the presence of beneficial insects.
Aphid Control: Convergent Lady Beetle
The convergent lady beetle is a very common species of lady beetle among the numerous others present in any crop field. The convergent beetle is common in Alabama and also a very popular beneficial insect sold by companies. The insect name comes from the two white lines seen on the thorax of adult beetles that seem to merge together on the top.
The number of dots can vary from none up to 13, so counting the dots alone is not a good identifier for this beetle. Larvae are black with rows of orange spots. Note that the lady beetle larva have chewing mouthparts and do not have the sickle shaped mandibles of the green lacewing larva. Eggs are elliptical and bright yellow in color; eggs are laid in clusters on plants with over 10 eggs per cluster. Eggs can also be laid in soil or plant debris. Pupae are immobile (non-feeding stage) and may be seen stuck to plant parts.
Adults and larvae feed on aphids. Adult beetles also feed on nectar and pollen. According to industry sources, each adult lady beetle can destroy about 5,000 aphids while the larvae can consume nearly 400 aphids in a week. In the absence of aphids, convergent beetles can also feed on moth eggs and small caterpillars. Female convergent beetles lay up to 1,000 eggs in ideal conditions and have a lifespan of one to three months. Larvae feed for three weeks and adults emerge two to five days after pupation.
Adults do not fly if air temperatures are below 55°F. There can be many generations of this insect every year.
The presence of a large number of lady beetles can indicate the presence of aphids. This insect can be the most abundant predator in cotton fields.
Many suppliers sell lady beetles in the adult stage when they are ready for field release (as shown in photo). The adult beetles can also be stored in their original package for some duration; provide some moisture to the lady beetles by sprinkling water on the packaging before release. Release lady beetles preferably during a cool evening. Lady beetles should be released when pest pressures are low and the beetles have something to feed on. Several weekly releases may be necessary to sustain a high predator pressure in an area. Industry sources recommend the release rate of 4,500 beetles for 2,500 square feet and much larger numbers for large areas. Out migration of adults once prey numbers dwindle is a major cause of loss of these powerful natural control agents.
Routine inundative release of beetles in large numbers can be effective in enclosed structures for aphid control. Remember that parasitoids and pathogens also act in conjunction with predators to provide natural control of pests. Do your own research before purchasing large batches of predators and carefully plan the release for the best effect. Follow the instructions that come with your purchase of beneficial insects.
Providing cover crops or shelter plants during the fall season is a good way to facilitate continuity of predators in an area.
Editor’s Note: This article appeared in the November 2012 issue of Acres U.S.A.
Dr. Ayanava Majumdar (Dr. A) is extension entomologist and state sustainable agricultural research coordinator at Auburn University, Alabama. Join him on the Alabama Vegetable IPM Facebook page for more information on sustainable crop production systems.