Botanical gardens have always had difficulty keeping plant viruses out of their orchid collections. While working at the U.S. Botanical Garden in Washington, D.C., Carol Allen often noticed small indentations or notches on the aerial roots of orchids in the conservatory. One evening, she saw cockroaches crawling over the roots. Could they be the culprits spreading viruses between contaminated plants and newly arrived virus-free plants? Always before, virus transmission between plants had been attributed to pruning tools or sucking insects such as aphids.
Allen, the 2009 recipient of the Francis R. Gouin Undergraduate Research Grant at the University of Maryland in College Park, has discovered that cockroaches can spread viruses from infected plants to healthy virus-free plants. With the Undergraduate Research Grant funded by my writing, she initiated a rather large experiment in cages using virus-free orchid plants with domestic and Australian cockroaches that had been allowed to feed on infected orchids. Four separate cages guaranteed accuracy.
The cockroaches were allowed to feed on the plants for five weeks. Evidence of feeding could be seen in injury to the roots and flowers. The virus-free plants were tested at monthly intervals. After 18 weeks, they were contaminated with viruses.
Allen’s findings were so spectacular that she was invited to present the results at the International Orchid Symposium in Taiwan in January. Her recommendations are that it is just as important to control cockroaches in greenhouses as it is to control plant-sucking insects in order to keep orchids free of viruses.