   Lady Beetles - June 11, 2003 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Aphids have many natural enemies, which naturally reduce their populations. One important natural enemy of the aphid is the lady beetle (also known as the "lady bug"). Knowing that lady beetles will arrive in your garden helps you tolerate spring aphid populations. Learning to recognize and appreciate lady beetles (and other natural enemies) will decrease your dependence on synthetic pesticides and increase your tolerance of relatively harmless pest insects such as aphids. Lady beetles are true beetles (Order Coleoptera) and in the family Coccinellidae. Most people recognize the adult lady beetle by its shiny, convex, half-dome shape. They are often orange with black spots. However, given over 500 species found north of the Mexican border, there is much variation in color: from bright colors with spots to dark colors with few or no markings. Most lady beetles are predaceous as both larvae and adults and vary in adult body length between 3 to 7 mm. Gardeners should learn to recognize lady beetle egg masses, larvae, and pupae to allow them to monitor populations. Egg masses are small, bright orange ovals laid on end in groups. Larvae are multi-colored, often mostly blue with red or orange markings and resemble little alligators. Larvae of most species go through four instars (stages between molts) looking similar but increasing in size each time. After the larval stage, the larvae pupate for a brief period before emerging as adults. The pupae are often attached to leaves, tree trunks, and structures and look similar to the larvae but are stationary and rounded. Photos of all life stages of the convergent lady beetle can be seen on the web at: www.ipm.ucdavis.edu/PMG/NE/convergent_lady_beetle.html. Lady beetles (and many other predacious insects) are cannibalistic. When larvae hatch from eggs they begin to feed on nearby unhatched eggs and other small larvae. The voracity of small larvae is relatively low. First and second instar larvae kill 2-20 aphids per day. Third and fourth instars feed on more aphids, with fourth instars consuming as many or more aphids than second and third instars combined (also more than adults). Therefore, to maximize aphid control, lady beetle lifecycles should not be interrupted by insecticide applications or other disruptive activities. The eyesight of lady beetles is poor and beetles have to almost touch aphids in order to detect them. Once an aphid is found and consumed, however, the beetle intensively searches the immediate area. In addition, lady beetles respond positively to light and negatively to gravity and intensify search behavior when aphid honeydew is encountered. Since aphids are congregated in colonies in the upper parts of the canopy, this search pattern tends to bring predators in contact with prey. Not all aphids encountered are eaten; however, disturbance by lady beetles may make aphids more vulnerable to attack by other predators. Adults can fly and are fairly resistant to starvation. When aphid populations decline, lady beetles migrate to cooler regions (often mountain tops). Here, they feed on pollen and nectar. As cold weather sets in, they migrate to canyons and aggregate in large numbers. Here, they remain inactive until temperatures start warming up. In the spring, adults fly down from the mountains to valley areas. Commercially available lady beetles are sometimes collected at overwintering sites and can be bought and released. Unfortunately, lady beetles have the tendency to disperse once they are released, even if food is abundant. Although they are extremely important natural enemies of aphids, their tendency to disperse makes it difficult to introduce them to a specific area to control aphids. It is best to simply let them come and do their job where and when aphids are present. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |