Tiny Game Hunting

Environmentally Healthy Ways to Trap and Kill the Pests in Your House and Garden

Hilary Dole Klein and Adrian M. Wenner

There is something very discouraging about a plant infested with whiteflies.
If you shake it, these tiny, mothlike creatures fly up from the undersides of the leaves in great numbers. When they settle back down, they select an even fresher and more tender leaf than before.

Only about one-sixteenth of an inch long, covered with a powdery wax, and sometimes called "flying dandruff," whiteflies reproduce fast (generally in a month or less), can build up in great numbers, and are known for developing quick immunities to pesticides. Each whitefly lays twenty to twenty-five practically invisible eggs in a circle around herself. These hatch into scalelike larvae or nymphs, which move around for a few days before picking a spot and settling in.

A new whitefly pest recently reached Southern California, the giant whitefly (though it is minuscule by our standards and is known elsewhere as the spiraling whitefly). It infests more than a hundred species of plants, including many of the exotic varieties that California gardeners love, such as hibiscus, banana, canna lilies, cherimoya, and citrus. The female giant whitefly lays a spiral of eggs on the underside of a leaf. As the nymphs develop, they spin out hairs, until the leaf appears to have a white beard. These hairs prevent significant penetration of any sprays directed toward them. A parasitoid, Incarsia sp., may eventually prove effective, but for now few controls exist against this new pest.

An abundant whitefly infestation can cause a plant to wilt, fade, droop, and die. The honeydew they secrete nourishes a sooty mold, which grows and also damages plants.

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Control
Yellow sticky traps are quite effective with whiteflies, which are drawn to this color. Place traps on a stick or hang them slightly above the plant; the whiteflies' tendency to fly upward and to land on yellow will do them in.

You can buy sticky traps or make your own from pieces of yellow plastic, stiff paper, or cans, coated with a sticky substance. In addition to commercial sticky substances such as Stikem Special and Tanglefoot, people have used vegetable oil from a spray can, mineral oil, molasses, and petroleum jelly.

One gardener we know uses a two-by-three-foot sheet of stiff, sticky yellow paper nailed to a stake. She plants it in the ground behind the plant, then lightly sprays the plant with water from the opposite side, forcing the whiteflies off the plant and onto the trap.

Sprays can reduce whitefly populations, but they have to be applied fairly frequently--every four or five days for several weeks. Effective sprays include homemade soap spray, insecticidal soap spray, horticultural oil, and alcohol/soap spray. Use pyrethrum only as a last resort. Don't neglect the undersides of leaves.

There is a good chance that phosphorus- or magnesium-deficient plants play host to these pests. Try to adjust the soil chemistry to include these nutrients. Plant marigolds and nasturtiums.

You can also suck up these pests with a portable vacuum cleaner. Shake the plant to disturb the whiteflies. To make the job even easier, wrap the end of the vacuum cleaner tube with bright yellow electrical tape. The whiteflies will fly toward the yellow end and you can suck them right up. As with handpicking, this method works well on cool early mornings, when the insects are sluggish. Put the vacuum cleaner bag in the freezer to kill the bugs. Do this once a day for several weeks.

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Natural Enemies
Ladybird beetles and lacewings eat whitefly larvae, but the best control for this pest is Encarsia formosa, a minute parasitic wasp, also known as the whitefly parasite, which lays its eggs in the whitefly nymphs. In greenhouses, this wasp can control the population of whiteflies to the point where damage is negligible.

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