Don’t let the lady beetle’s adorable appearance fool you. These beetles, both adults and their larvae, are voracious predators and play an important role in controlling rice pests, including leafhoppers and planthoppers.
Lady beetles, also known as “ladybirds” or “ladybugs,” are one of the rare insects that do not seem to have the “ick-factor.” These delightful beetles (Coccinellidae) are a favorite of children and have been turned into toys, trinkets, and motifs. They populate art, literature, TV, and films. One can even find lady beetle-inspired confections.
In living colors
Why they have become celebrities of the insect world is easy to see. Coccinellids, with more than 5,000 known species, can be found in every corner of the planet except the North and South Poles. But, regardless of where they live, the entire family shares a common trait—an outrageous “fashion” sense.
Depending on the species, lady beetles come in shimmering red, yellow, brown, black, or gold. Many have from 2 to more than 22 bold black spots. Black ladybirds may have orange or yellow spots that just scream for attention. Still others, instead of spots, carry what appears to be tiny brush strokes painted frivolously on their oval, domed backs or hardened forewings called elytra.
The bright colors of the lady beetles are not an indication of the cheerful demeanor that has been attributed to them. The loud hues are actually warning colors (aposematism) designed to ward off would-be predators. Lady beetles secrete a bad-tasting fluid from the joints in their legs and their colors “advertise” that they should be left alone.
However, their appearance is not the only factor that makes them a great species to have around. These beetles are voracious predatory insects that feed on mites, mealybugs, leafhoppers, stem borers, thrips, scale insects, and other small soft-bodied insects as well as eggs and larvae or nymphs of these insects. The average adult lady beetle, during its lifespan of about a year, can consume more than 5,000 aphids.
“Lady beetles are good predators of planthoppers, one of the most serious pests of rice,” said Dr. K.L. Heong, an insect ecologist at the International Rice Research Institute (IRRI). “Farmers should welcome their presence.”
Born to kill
Lady beetles are useful long before they become adults. A single beetle can produce as many as several dozen eggs on leaves where their larvae are likely to find sources of food upon hatching. Although their larvae look nothing like the attractive adults (in fact, they are quite ugly at this stage), they are just as useful.
“The larvae are voracious predators, and they feed on nymphs of planthoppers and the larvae of other pests found on rice,” said Dr. Heong. A single lady beetle larva will eat as many as 300 aphids before entering the pupa state. If a single female lady beetle can lay more than 2,000 eggs in her lifetime, do the math and the number of insect pests both larvae and adults consume is staggering and a great help to farmers.
The right way to treat a lady
Legend has it that English Catholic farmers in the Middle Ages believed that lady beetles were sent by the Virgin Mary, in answer to their prayers for help, to eat the aphids that were destroying their crops. Hence, they were called “Our Lady’s Beetle.”
Today, IRRI scientists are encouraging farmers to attract lady beetles, and other predatory insects, to their fields by creating a habitat where they can live and multiply. Lady beetles typically live in dense foliage such as hedges and trees, although others may prefer forests, fields, grasslands, or locations near waterways and wetlands.
For example, in the ecological engineering field at IRRI, these species are observed to feed on the nectar of flowering plants. Planting flowering plants on the bunds of rice fields provides sources of food and shelter for them.
The method known as ecological engineering restores and reinforces the diversity of natural enemies of rice pests to reduce the vulnerability of crops to pest invasions. Reducing the use of pesticides is a big part of the strategy (see Letting nature manage its battles on pages 32-34 of Rice Today Vol. 10, No. 4). At the same time, it also restores floral biodiversity. Minimizing disruptive factors such as withholding early-season insecticide sprays is a big part of the strategy. Insecticides should be used only as a last resort.
Mr. Santiaguel is a writer of Rice Today.