Florida is graced by sixteen native species of bromeliads, few of them found in any other state. Populations of some of them have been devastated by attack by an invasive pest weevil, Metamasius callizona. Eleven native bromeliad species are now threatened by this weevil.
|Metamasius callizona is a weevil of Mexican origin detected by Florida Department of Agriculture and Consumer Services inspectors at a nursery in Broward County, Florida, in 1989. By the time the weevil was detected, there was no hope of eradicating it by use of chemical pesticides - it had become feral and established populations in native bromeliads in Broward County parks. It was widespread and would have been very expensive to eradicate with chemicals, especially since the chemicals would have to be applied by helicopter so that they could hit epiphytic bromeliads. Moreover, the use of chemical pesticides (such as Dursban and Carbamate, which are useful in controlling the weevil in greenhouses, shadehouses, and private collections) is not permitted in parks because of the risk to non-target native insects.||
The Evil Weevil
|By 1991, this weevil was found to occupy parts of four South Florida counties. These were Broward, where it was first detected; Palm Beach, where it probably spread by dispersal; Lee, where it undoubtedly spread by movement of infested bromeliads, perhaps even as an independent introduction from Mexico; and southeastern Miami-Dade, where it likewise must have spread by movement of infested plants. The weevil attacked native tillandsia bromeliads in natural areas.||
Adult M. callizona
note damage from larval mining
Metamasius callizona is one of twenty or more species of pest weevils that are known to attack bromeliads in countries south of the U.S. There is little or nothing about them in books about bromeliads, perhaps because they don't seem very common in their native countries. But M. callizona is now far too common in Florida. By 1991, it had been found in only four Florida counties. By early 1999, it had been found in twelve more. It has invaded the Sebastian, St. Lucie, Loxahatchee, Caloosahatchee, Peace, Myakka, and Manatee river systems. By 1991, M. callizona had been found to attack the most abundant of the larger bromeliads in the areas it occupied: Tillandsia utriculata, T. paucifolia, and T. fasciculata. Bromeliad enthusiast Olan R. Creel has also seen it attack the threatened T. balbisiana and endangered T. flexuosa.
The 'Evil Weevil Targets Florida Bromeliads' table lists native bromeliads and their M. callizona "attack status." Tillandsia utriculata and T. fasciculata (for some reason, not T. paucifolia) were listed as endangered species because of attack by the weevil. Tillandsia fasciculata seems much more resistant to the weevil than is T. utriculata, but still may be killed.
Weevil eggs are laid in the largest bromeliads, and the resultant larvae mine the stems. The largest bromeliads, which take years to grow to that size, are the breeding population. As the breeding plants are killed, the plant population produces fewer and fewer seeds to replace dead plants.
What of Florida's other endangered and threatened species? They, too, probably will be attacked once the weevil reaches the restricted areas in which they grow. (M. callizona has attacked various cultivated Catopsis and Guzmania species in greenhouses). The table lists native bromeliad species which are vulnerable to attack as well as those which probably won't be attacked.
Looking at the distribution map, one can see that M. callizona is now very close to the natural areas that contain listed bromeliads. These plants are already very rare, with their rarity determined in part by their climatic needs. Another determinant of their rarity has been habitat destruction, from which they are not protected by Florida law. In federal and state parks and nature preserves, the plants are protected from developers, but not from the weevil. Florida law does not mandate that anything be done to control an invasive pest such as M. callizona that kills endangered plants. The weevil is now killing bromeliads in the Savannas State Preserve (St. Lucie County) and Highlands Hammock State Park (Highlands County). It is on the verge of the Big Cypress National Preserve and the Fahkahatchee Strand State Preserve (both in Collier County).
The calamity that has befallen T. utriculata and other species in southeastern Florida is likely to be repeated with other species (see table). There is one action that might slow destruction by the weevil and give the bromeliads a chance. That action is biological control.
Metamasius callizona and its close allies just don't seem very common in their native countries. One possibility that may account for this is the existence of specialized natural enemies (insect parasitoids - perhaps tiny wasp larvae or fly larvae) that kill some development stage of the weevil. It should be no surprise that nobody has made a survey of such natural enemies, because the weevils are of little consequence in their native countries. And to make a thorough survey would be expensive, because of the need for extensive travel to find not just the weevils (which are not common), but to find weevils under attack by natural enemies, and then one must devise methods to rear and study the natural enemies. Even identification could be difficult because of the probability that such insects would be new species (unknown to science).
Dr. Ronald Cave (El Zamorano, Honduras) is an entomologist who teaches at an agricultural college and likes to collect and study insects, especially beetles, in his spare time. Weevils are one of the families of beetles. [See Dr. Frank's website for more general information about weevils.] Dr. Cave collected larvae of the weevil Metamasius quadrilineatus in bromeliads in Honduras, and that species is very closely related to M. callizona, and has very similar habits, including a diet restricted to bromeliads. Some of the live weevil larvae that he collected died, and from their corpses emerged fly larvae, the cause of death.
The fly found in Honduras by Dr. Cave belongs to the genus Admontia, and is an undescribed species new to science. Admontia belongs to the fly family TACHINIDAE, all of whose species, in their larval stage, attack other insects. Many of these tachinid flies are highly specialized, each attacking only one (host) species of insect, or a few species that are very closely related. So, there is a possibility that it can also attack M. callizona and perhaps other bromeliad-eating Metamasius weevils. There also is a possibility that it could, if introduced, establish a population in Florida, reduce M. callizona populations, and save Florida's native bromeliads from destruction. There is a possibility that it may be found harmless to all other insects - having no non-target effects. All of these possibilities need detailed research.
Most of the costs of the research that has been done to date on M. callizona in Florida and on the undescribed Admontia fly in Honduras has been supported by the Florida Council of Bromeliad Societies (FCBS). Members of FCBS have held sales of ornamental, non-native bromeliads and have donated the proceeds to pay for the cost of travel, supplies, and student labor.
The Florida State Legislature approved an increase to $30 million for funds to combat invasive plants that threaten Florida's native plants and natural areas. But there is no state funding program to combat invasive insects that threaten Florida's native plants. Minimally, a full-time post-doctoral researcher is needed now to work on biological control of M. callizona, but there are no funds to pay for this.
FCBS members are concerned about Florida's native bromeliads, and have been generous. But, far from the research being nearly finished, it must now expand to discover whether biological control possibilities are real and, if they are real, to produce large numbers of the flies for release in Florida. More research funds are needed to pay for temporary personnel, and costs will be far more than FCBS can support.
M. callizona is poised to attack the rarest of the native bromeliads. Research is urgent as results are needed now.
ABOUT THE AUTHOR: Dr. Frank is a professor at the University of Florida and has a Ph.D in entomology from Oxford University, England. Seventy percent (70%) of his time is dedicated to research into biological controls of pest insects, using parasitoids, predators, or pathogens. He is the author of three books, 110 refereed papers, and dozens of other publications. You can contact him at the Entomology & Nematology Department, University of Florida
Probably will be attacked by M. callizona:
Tillandsia pruinosa - fuzzywuzzy airplant - endangered
Tillandsia variabilis - leatherleaf airplant - threatened
Guzmania monostachia - West Indian tufted airplant - endangered
Catopsis berteroniana - powdery strap airplant - endangered
Catopsis floribunda - Florida strap airplant - endangered
Catopsis nutans - nodding strap airplant - endangered
Probably will not be attacked by M. callizona:
Tillandsia bartramii - Bartram's airplant
Tillandsia setacea - southern needleleaf
Tillandsia simulata - no vernacular name
Tillandsia recurvata - ball moss
Tillandsia usneoides - Spanish moss
NOTE: These five Florida native bromeliads are unlikely to be attacked by M. callizona because they seem to be too small to be mined by the larvae.
Common names of the bromeliads listed above are taken from Richard P. Wunderlin's Guide to the Vascular Plants of Florida (University Press of Florida, 1997). Listed status (endangered/threatened) is as listed in the 1998 Florida Administrative Code under authority of the Florida Statutes.