Delphastus pusillus is a small native ladybird beetle from Florida with a wide distribution across the central and southern U.S. It is also found in Central America, the Caribbean and in South America as far south as Peru. D. pusillus attacks all species and stages of whiteflies, but prefers eggs and nymphs.
The adults are small (1/16 inch), shiny, black beetles. They are strong fliers that will immigrate into areas that contain high densities of whiteflies. D. pusillus responds to odors emitted by immature whiteflies, so it can find congregations of them easily among the foliage. The beetles tend to fly around more on overcast days.
Female beetles live for about 2 months, during which time they lay 3 to 4 eggs per day. (Male beetles live for 1½ months.) They generally lay their eggs within clusters of whitefly eggs, which makes it easier for the young larvae to find a food source. The eggs are 0.2 mm long, clear and twice as long as they are wide. The elongate larvae are pale yellow. Each instar lasts 1½-3 days. D. pusillus pupates on lower leaves, in leaf litter, or in other protected locations, often in groups. The pupal stage lasts approximately 6 days. Newly emerged adults are pale-brown to almost white. They eventually turn black with a brown head. Development from egg to adult takes approximately 3 weeks at 80-85ºF.
Both larvae and adults are active predators that can consume numerous eggs or nymphs each day. An adult Delphastus takes no longer than half a minute to handle a whitefly egg, and devours up to 160 eggs or 12 large nymphs daily. A larva consumes 1000 whitefly eggs (less if it also eats whitefly nymphs) during its entire development. Adults and larvae feed by piercing the insect with their mouthparts and alternately sucking and regurgitating the internal contents to digest and consume it. Adult females feed more on eggs and first instars than on later stages.
D. pusillus performs best at temperatures between 65 and 90ºF and when relative humidity is above 70%. Beetle searching, feeding, and egg laying may be inhibited by plants with dense trichomes (hairs). Therefore this natural enemy may not be suitable for use against whiteflies on some plants, such as many varieties of tomato. In addition, adult movement is inhibited by excessive amounts of honeydew produced by the whiteflies. Beetles are slowed down or trapped in the sticky exudate.
D. pusillus has the potential to decimate large populations of whiteflies in the greenhouse since a single beetle can consume 10,000 whitefly eggs in its lifetime. However, since adult female beetles must feed on over 200 eggs per day in order to reproduce; these beetles are unlikely to persist when whitefly numbers are low.
D. pusillus can be used in conjunction with other biological control organisms. Both adult and larval beetles avoid feeding on whitefly nymphs parasitized by wasps such as Encarsia formosa and Eretmocerus eremicus when the wasps are in later stages of development. In some experiments whitefly control was better when the beetle was released simultaneously with a wasp, than when the natural enemies were released alone.
D. pusillus, which is commercially available, is normally shipped as adults, often in a tube filled with shredded paper or other cushioning material. Upon arrival, these predators should be released immediately, although the beetle can be stored briefly at 59-68ºF. Releases should be made in the early morning or evening (dusk) near areas of high whitefly populations.
D. pusillus is most effective at high whitefly densities, so it may be of limited benefit in greenhouses where whitefly populations are kept at low population levels by other means. But even in these situations it can be useful as a rescue treatment to help suppress "hot spots" where whitefly colonies are increasing.
- Raymond A. Cloyd, University of Illinois
|Return to Contents Menu Vol. VI No. 10|
Go To Index