Adenium Caterpillar

The Amazing Adenium

• The desert rose's succulent, water-storing branches fan out from a thick base contorted with engorged reptilian humps. The plant’s sparse foliage and five-petaled, white, pink, red or purple blooms sprout from the tips of the twisting, gray-green branches. Despite its lack of thorns, this isn't a kid- or pet-friendly plant. Its defense against predators is a milky sap that tribal hunters in its native African habitat use as arrow poison for felling big game. In the southeastern United States, desert rose shares a common pest with another poisonous plant -- it hosts the oleander caterpillar common on oleander shrubs (Nerium oleander), which are hardy in USDA zones 9 through 11.

Colorful Culprits

• The oleander caterpillar may be the only creature capable of toppling the spider as the Halloween creepy-crawly of choice. It certainly dresses the part, with black bumps all along its bright orange body sprouting tufts of stiff black hairs like the warts on a cartoon witch's chin. The caterpillar outdoes the most enthusiastic trick-or-treater by eating its way from 1/10 inch to 1 1/2 inches long before pupating. That's a nearly 16-fold increase in less than a month for the offspring of the polka-dot wasp moth, an iridescent, blue-green red-tipped insect peppered with white spots.

Feeding Damage

• Newly hatched oleander caterpillars feed in groups on the undersides of leaves. To survive their toxic diet, they nibble precisely between the desert rose's sap-filled veins and stems. Older caterpillars graduate to solitary meals of entire leaves, blocking sap flow by cutting through the stems and defoliating the plant. A desert rose robbed of its foliage doesn't die, but yearly defoliation raises its risk of continual insect attacks.

Defending the Desert Rose

• Oleander caterpillars have numerous insect predators, including red imported fire ants, stink bugs and predatory wasps. If these insects fail to control the pests on your adenium, simply prune shoots infested with young caterpillars, and then seal them in a plastic bag and freeze them for 24 hours. Wear waterproof gloves when cutting and handling the leaves to protect your skin from the poison sap. Handpick and drown larger caterpillars in soapy water.

Using Microbial Control

• If you're hesitant about pruning or hand picking, treat your desert rose with a solution of 4 teaspoons -- or the label's specified amount-- of Bacillus thuringiensis powder in 1 gallon of soft water. Check the undersides of the leaves each day for masses of tiny, creamy-white eggs. When the last mass has hatched, gently but thoroughly spray the caterpillar-infested leaves. It's best not to spray the plant in full sun. Bacillus microbes pass through the pests’ gut walls and kill them with blood poisoning.