UF Researchers test natural predators to control sago palm threat
Chuck Woods (352) 392-0400
GAINESVILLE, Fla. — In a prime example of how an exotic insect can wreak havoc on landscape plants and cause millions of dollars in damage, the Asian cycad scale has invaded South Florida and quickly spread throughout the state.
The tiny pest’s only host is the cycad – also called a sago palm – and experts say the scale is probably the single most important threat to wild cycad populations around the world.
Its rapid spread in Florida suggests that the insect has few effective natural enemies in the state, said Catharine Mannion, an assistant professor of ornamental entomology at UF’s Institute of Food and Agricultural Sciences.
“The insect began attacking the plants in South Florida in the mid-1990s, when the pest was accidentally introduced to the Miami area from Southeast Asia,” she said. “Within a few years, 80 percent of the king and queen sago palms in South Florida were killed, and the pest has killed almost half of the king and queen sago palms in Central Florida. The cycad nursery industry has been devastated, with economic losses in the millions.”
She said two commonly grown cycads – king and queen sagos – are susceptible to attack by the Asian cycad scale. An infestation can coat a medium-sized sago within months and kill it within a year.
“In areas with high infestations, management of the pest will be a continuous and long-term effort,” Mannion said. “If infested cycads go unmanaged, the scale will not only kill the cycad but can be spread to other cycads.”
Researchers at UF’s Tropical Research and Education Center in Homestead have introduced two natural enemies to help combat this pest, but they are not completely effective. The insects were imported from Thailand and released in South Florida in 1997 and 1998.
The natural enemies are a predaceous beetle and a parasitic wasp. The adult beetle feeds primarily on adult female scale. The beetle lays her eggs among the scale eggs underneath the scale armor covering. After hatching, the beetle larva feeds on all stages of the scale. The wasp attacks and kills female scale by laying its egg inside the female scale where the developing wasp larva feeds and grows.
“Both of these natural enemies have become established in many areas of South Florida and contribute to the control of the scale,” said Mannion, who is based at UF’s Homestead center. “However, because of the explosive nature of the scale insect, neither one of these natural enemies can provide complete control.”
Ronald Cave, an assistant professor of entomology at UF’s Indian River Research and Education Center in Fort Pierce, recently went to China and Vietnam to identify parasitoids that could be imported and released in Florida. Two types of parasitic wasps were taken to quarantine facilities in Gainesville and Fort Pierce, where methods are being developed to rear the wasps for research purposes.
Mannion is also evaluating another potential predatory beetle that was introduced into Hawaii many years ago for control of other armored-scale insects and reportedly provides some control of the Asian cycad scale. Small, isolated populations have been found in Florida, but early indications are that it may not be contributing much to the control of this pest, she said.
Horticultural oils and/or insecticides can be used to manage Asian cycad scale, she said. Thorough coverage of the plant is extremely important when applying a spray and repeat applications may be necessary, Mannion said.