The spotted lady beetle (Coleomegilla maculata) preys on aphids, spider mites, and other plant-damaging pests, making it a possible biocontrol agent — an organism that is used to control pest organisms. However, there has never been an easy way to raise these lady beetles, until now perhaps.
The USDA’s Agricultural Research Service has developed new technology that allows users to harvest thousands of eggs daily. Entomologist Meg Allen devised a jar-like cage to safely collect the eggs of Coleomegilla maculata for her research on the genetics of this helpful ladybug species. The new system is easy to use and less messy than traditional systems.
“One of the shortcomings of lady beetles for biological control is they can fly!” Allen said. “When they’re sold as adults, they don’t stay on the plants in your garden. If they were sold as eggs, they would hatch and the larvae would walk on the plants and eat pests before maturing.”
ARS is interested in the spotted lady beetle because of its potential for use in biocontrol programs. Native to the United States, it’s a generalist predator that hunts for prey in many economically important crops, including wheat, corn, cotton, alfalfa, soybean, pea, and tomato, among others. Unlike the multicolored Asian lady beetle (Harmonia axyridis), the spotted lady beetle doesn’t invade homes during the winter and become a nuisance. It can also survive on pollen when prey is scarce, adding to its versatility as a biocontrol agent that could diminish the need for insecticides.
Prior to conducting her genetics studies, Allen searched for an easy-to-use, standardized method of collecting eggs from laboratory colonies of the ladybug. Finding none, she custom-built a system from scratch using off-the-shelf supplies.
The system comprises a squat jar and mesh-screen lid fitted with several strips where female ladybugs can deposit their eggs. In designing it, Allen considered both her need for a steady supply of eggs from which to extract DNA for genetic analysis and the ladybug’s own behavior, particularly its egg-laying preferences. For example, the beetles chose textured strips instead of smooth, waxy ones — perhaps because, in nature, females prefer plants with tiny surface hairs, called “trichomes.” Laboratory experiments (co-reported with ARS entomologist Eric Riddick in January 2012 in the journal Psyche: A Journal of Entomology) confirmed the observation. On average, females deposited 150 percent more egg masses on textured strips than on smooth ones.
Hanging the strips from the jar’s center also reduces cannibalism and ensures that the eggs can be quickly and safely removed as needed. For large-scale egg collection, Allen uses a six-jar configuration that houses 10-20 female ladybugs each and enables collection of a couple hundred to a few thousand of egg masses a day.
“I hope this system will be adopted throughout insect-rearing facilities,” she said. “It can be scaled up and there are all sorts of ways it can be adjusted for different species and quantities.”