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Living With Houseplants and Their Insect Relatives

FOR IMMEDIATE RELEASE
November 15, 2012

"Insect relations" often accompany the plants that are brought indoors, and they never seem to leave, said a University of Illinois Extension horticulture educator.

"Sometimes even our best attempts aren't enough," said Richard Hentschel. "You wake up some morning a few weeks after your houseplants have been inside and see something that is not quite right on the plants or maybe in the window trying to get out. The insects are not always closely associated with our houseplants but happened to be on the plants at the time they were brought in."

Such insects are unlikely to be a problem. They do not feed on the plants, and without food and in the wrong environment, they will die on the window sill.

For example, boxelder bugs wander around the home, living on the food they have stored up in their bodies and will not survive. They leave behind little black spots of the food they digested, so it is better to deal with them immediately to avoid having to do a cleanup later.

"The insects that are troublesome outside are the ones that will cause the problems on the inside as well," Hentschel said. "Outdoors there are natural predators that keep the populations in check and weather events such as rainstorms that help reduce the number of insects on the houseplants. Inside the house, we don't have rain events, and without natural predators, the populations of offending insects will quicly grow in number, living on the houseplants."

Two of the more common houseplant insects during the winter months are spider mites and scale insects. Spider mites, which come in several colors, do not have chewing mouthparts. They scratch the plant tissue and feed on the sap that oozes out. Mites can also spread digestive juices in their feeding area, destroying more tissue for consumption.

"Mite damage will sneak up on you. Insects start out on the underside of the leaves and in low numbers," Hentschel explained. "Later, as their numbers explode, you will see them by the thousands near the vegetative growing points and flower buds among very fine webbing. When you find them this way, you know you have an outbreak needing immediate attention."

Rinse off the nymphs and adults with strong streams of water, such as the sink attachment in the kitchen, or give them a shower in the bathroom if the plant is too big for the kitchen sink. Plan to do this again after a few days because the leftover eggs will hatch and restart the cycle. A month or more of treatments may be needed. The goal is to break the life cycle and not let an adult lay any more eggs.

The second common houseplant insect that can survive indoors, and is hard to get rid of before bringing the plants indoors, is the scale insect. They live and feed on the houseplants and will increase in number indoors. They leave a clear sticky material on the leaves or a sticky mess on the floor below the plant on the hardwood or carpet.

"Scale insects insert their feeding tube into plant tissue and begin to remove the plant sap to feed on," he said. "As they feed on the sap, the excess is expelled and drips downward where we see it as that shiny, sticky surface."

The adult scale is firmly attached and protected on the plant stems. The offspring is a very small, fleshy insect resembling an aphid that can be dislodged. The adults take a lot more effort as they are protected by their scale. Getting rid of scale insects is a lot more work than spider mites. An insecticide labeled for use on houseplants may be needed.

These two common insects are above-ground insects. Other animals can live in the pot itself, such as pillbugs, also called roly-poly bugs (because they roll up into a ball), which love humidity and feed on organic matter. Watering the houseplant will temporarily force them out of the pot. Watering well also forces out earwigs, which are common in potting soil. Be sure to do this in an area where the bugs can be rinsed away.

On occasion, there can be an outbreak of even the common aphid indoors. Aphids give live birth, so using the rinse nozzle on the kitchen sink or the bathroom shower will usually take care of the problem.

"An added benefit of all that plant rinsing is that plants that are not covered with household dust will have higher rates of photosynthesis and be healthier," he said. "One of the better things we can do during any holiday season is to separate the holiday gift plants from the general population of houseplants. This helps guarantee that houseplants remain insect-free."

Source: Richard Hentschel, Extension Educator, Horticulture, hentsche@uiuc.edu