Like the holly we visited last week in Bug of the Week, ivy is another popular plant commemorated in the venerable Christmas carol “The holly and the ivy”. The Romans wore crowns of ivy to celebrate Bacchus, god of wine. Pagans and Christians alike considered ivy a symbol of eternal life. Intertwined garlands of holly and ivy have been used since ancient times to represent the dual nature of life, holly representing the female aspect and ivy representing the male. During the holiday season holly often graces our office as part of the festive decorations. On occasion, our lovely ivy comes down with a bad case of the holiday blues – brown unsightly leaves dropping from the plant. What Grinch was at work here?
Several insect pests make their presence known on houseplants during the holiday season. This holiday surprise is a formidable pest, thrips. Thrips are strange little insects with an unusual name that is both singular and plural as thrips. They have equally strange and formidable mouthparts. A dagger like jaw punctures the leaf and other ingestive contrivances slurp up the nutritious juice. Thirps feeding causes discolored, flattened areas or silver streaks on the surface of a leaf. The immature stages of thrips, called nymphs, are translucent yellow. They cannot fly and molt several times before transforming into winged adults capable of flight. Depending on the species, adults can be yellow to dark brown in color. Their tiny wings, lined with featherlike hairs, are the source of their Latin name, Thysanoptera, which means “feather wing”.
Female thrips can lay scores of eggs. Indoors where plants are warm and dry during winter months, thrips may complete a generation in about two weeks. It is easy to see how just a few thrips on a plant at Halloween can generate thousands by Christmas. In addition to damage caused as they feed, thrips leave behind little gifts in the form of black fecal deposits. These small treasures litter the surface of the leaf and collect on countertops or desks below the plant. How sweet! A vigorous washing with a spray of water may dislodge some of the thrips and provide a modicum of relief. However, the female embeds her eggs into the leaf surface and these are unlikely to be dislodged by a sloshing. Some insecticides are available to kill thrips, but a more natural and entertaining way to manage them is to release hungry predators with a taste for thrips. Greenhouse growers manage these villains by releasing predatory mites or minute pirate bugs that attack and eat thrips while they cavort on the leaves of plants. Just before thrips nymphs molt into a pupa they move to the base of the plant or soil. Here they are susceptible to control with entomopathogenic (insect killing) nematodes. These tiny roundworms can be purchased and sprayed on the plant and soil to kill developing thrips. The nematodes invade the body of the thrips and release a lethal bacterium. While a gift of predators or nematodes might be naughty for your thrips, it would be nice for your house plants. When plants are heavily infested with thrips, sometimes the best strategy is to say goodbye to the old ones, and “gift” yourself a new one.
Before dashing off to find the next meal a thrips takes a moment to groom its tail hairs.
We thank Jo Ann, Tamma, Bill, and Eileen for sharing their ivy and thrips for this episode of Bug of the Week.
For more information on thrips and their control, please visit the following web sites: