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. Through time, people of many faiths displayed ivy to symbolize eternal life. Intertwined garlands of holly and ivy have been used since ancient times to represent the dual nature of life, ivy representing the female and holly the male. During the holidays, the Department of Entomology is bedecked in its finest trimmings to celebrate the season. Part of our festive display is wonderful, variegated ivy.
A few weeks ago, our ivy came down with a bad case of the holiday blues. Several leaves turned brown and dropped from the plant while others withered. What Grinch was at work here? Many insect pests make their presence known on houseplants during the holiday season. In previous episodes we visited mealybugs and whiteflies. The little nightmare before Christmas on our holly was one of the pesky thrips, likely the greenhouse thrips, Heliothrips haemorrhoidalis. We met a close relative of this bugger, the Cuban laurel thrips, in a previous episode of Bug of the Week.
Thrips are strange animals with mouthparts that rasp the surface of a leaf then slurp up nutritious juice. Their feeding causes discolored flattened areas or silver streaks on the leaf’s surface. Immature stages of thrips are translucent yellow or light brown and these stages, called nymphs, cannot fly. They molt several times before transforming into winged adults capable of flight. Adults can be yellow to dark brown to almost black. Tiny wings lined with a featherlike fringe of hairs are the source of their Latin name, Thysanoptera, which means “fringe wing”. Female thrips lay scores of eggs during their lifetime. Indoors, where plants are warm and dry during winter months, thrips may complete a generation in roughly 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 leaf and collect on countertops and other surfaces below the plant. How festive! Some suggest that a serious washing with a powerful spray of water can dislodge thrips and provide a modicum of relief. However, the female embeds eggs in the leaf’s 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 might be to release hungry predators with thrips on the menu. Greenhouse growers manage these villains by releasing predatory mites or minute pirate bugs that attack and eat thrips. While a gift of predators might be naughty for your thrips, it would be nice for your ivy. 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.
We thank Jo Ann, Tamma, Bill, and Stephanie 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.