Weevils That Eat Bromeliads | Pests of Bromeliads | Bromeliad Biota

Biological Control of Metamasius callizona

Metamasius callizona has devastated populations of Tillandsia utriculata at sites in southeastern Florida. For this reason, at the urging of the Florida Endangered Plant Council, T. utriculata has been declared an endangered species in Florida (Florida Statutes). The weevil causes lesser damage to T. fasciculata, but this species, too, has been declared an endangered species (Florida Statutes). The full range of native species that it will attack in Florida is yet unknown, but does include T. paucifolia, which for some reason has not been declared an endangered species.

What can be done to reduce populations of M. callizona to save populations of T. utriculata - and of other native bromeliads? Use of pesticides is out of the question in natural areas for several reasons: (1) it would be extraordinarily expensive, (2) it would be of questionable effectiveness, and (3) it would not be permitted because of likely non-target effects of the pesticides. The only other way of saving the native bromeliads is by classical biological control, which relies on importation, release, and establishment of one or more specialist natural enemies.

Surveys for Metamasius callizona in southern Mexico in 1992 (Frank & Thomas 1994b) and 1995 (Frank, unpublished) showed that this species is not abundant - its populations do not reach the densities in which they were observed at localities in southeastern Florida. On the other hand, no shortage of host plants was seen in southern Mexico. This strongly suggests that M. callizona populations are limited in their homeland by natural enemies. Although the above-mentioned surveys in Mexico found generalist natural enemies in bromeliads, they found no specialists which could be used as biological control agents. It may be that continued intensive surveys would detect natural enemies in Mexico, but this would take at least months of work for which there are no funds.

Fortunately, work by Ronald Cave in Honduras, funded by the Florida Council of Bromeliad Societies, detected existence of a natural enemy of Metamasius quadrilineatus. This natural enemy is a tachinid fly of the genus Admontia whose larvae (maggots) kill larvae of M. quadrilineatus and may also kill larvae of M. callizona. A research program to develop culture methods for this fly and to investigate its host range is now in progress (Cave 1996), funded by the Florida Council of Bromeliad Societies.

Declaration of a plant as an endangered species in Florida does not confer either state or federal research funds. The project is presently supported with a grant from the Florida Department of Agriculture and Consumer Services/Division of Plant Industry (DOACS/DPI), but research funds are limited.

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