By Vincent Lazaneo.
She is a killer but everyone likes her. Her good press is the envy of politicians and her image is iconic. But most people know little about her. Even gardeners, who like to see lady beetles—commonly called ladybugs—on plants in their yards, often are not familiar with the insect’s lifecycle and its role in nature.
The most popular lady beetle is the convergent lady beetle, Hippodamia convergens, which is often sold at garden centers. The adult beetles are about ¼-inch long and usually have thirteen black spots on their reddish-orange wing covers. Females lay small yellow eggs on end in clusters of 10-50. They hatch into tiny alligator-shaped larvae (see photo) that are black with orange spots on some body segments. (Some uninformed gardeners think the strange looking larvae are pests and try to kill them.) Mature larvae generally pupate on the upper leaf surface where they transform into the adult lady beetle. The entire life cycle from egg to adult takes between three and six weeks depending on temperature.
Lady beetles are beneficial predators. Adults prefer to eat aphids. The larvae also feed on other soft bodied pests and insect eggs. One larva will eat about 400 medium-sized aphids during its development to the pupal stage. A new adult beetle must eat about 300 aphids before it lays eggs and thereafter needs to eat between three and ten aphids for each egg it produces. During its life, a single adult lady beetle may eat over 5000 aphids.
The convergent lady beetle is a migratory insect. Adults feed and reproduce in the central valley from spring to fall and have up to six generations annually. The beetles store body fat and beginning in mid-May fly to the foothills of the Sierra Nevada where they hibernate in large aggregations through winter. Beginning in late February, they return to the valley.
The aggregating beetles are easy for collectors to capture, store, and sell. Unfortunately for gardeners, nature designed the hibernating lady beetles to fly and disperse, which is what most lady beetles do when people buy and release them in a garden. To slow their departure, follow these tips.
Buy healthy lady beetles stored in refrigeration. They rapidly dehydrate at room temperature.
Lightly mist lady beetles with water at home to give them a drink, then store them in a refrigerator until released. Do not let water puddle in the container.
Release lady beetles in the early evening or at night when the temperature is cool. They will fly away almost immediately if the sun is shining, particularly if the temperature is above 65°F.
Release lady beetles on plants with a good supply of aphids.
Before lady beetles are released, spray plants with a fine mist of water.
Place lady beetles at the base of plants or in the crotches of low plants. They will crawl higher in search of aphids.
Don’t release lady beetles on plants recently treated with an insecticide that has a toxic residue.
Expect most lady beetles to fly away in a few days. About 95% of beetles in a research study flew away in 48 hours and the remainder were gone within five days. Lady beetles are unlikely to lay eggs on the plants they are released on. In one study, to control aphids on one heavily infested rose bush, two applications of 1,500 lady beetles each, spaced a week apart, was required.
The best way to control aphids and other pests in the garden is by protecting and promoting populations of lady beetles and other beneficial insects that already exist in gardens. Tolerate low populations of aphids on some plants so their natural enemies will have prey to feed on. If aphids or other sap feeding pests become too numerous, try washing them off with a forceful spray of water.
When an insecticide is needed, use insecticidal soap, horticultural oil, neem oil, or pyrethrin (derived from the seed pods of Chrysanthemum cinerariaefolium). These insecticides do not harm beneficial insects that contact treated foliage after the spray has dried. To control caterpillars, use a product containing Bacillus thuringiensis (Bt).
Vincent Lazaneo is UC Urban Horticulture Advisor Emeritus. He has a master’s degree in horticulture and a teaching credential in vocational agriculture from UC Davis. In 1983, Vince began the Master Gardener program in San Diego. Vince frequently contributes to the San Diego Union-Tribune and other publications and he enjoys growing specialty plants in his home garden, reading, hiking, and fishing.
Photo credit: Jack Kelly Clark, courtesy University of California Statewide IPM Program