Management options are limited for the invasive Mexican bromeliad weevil, which is devastating populations of Florida's native bromeliads. The epiphytic habit of the bromeliads and their presence in parks makes chemical control of the weevil in natural areas impractical and undesirable. Moreover, although there is a native species of bromeliad weevil (Metamasius mosieri) in the state, no natural enemies of either are known from Florida.

The solution in a case like this is to utilize a type of biological control (the use of natural enemies to manage pest populations) called classical biological control, which involves the importation of the pest's specialist natural enemies from its native land and subsequent release so that they will become permanently established. Classical biological control is applied to both insect pests and weeds.

In the case of an insect pest, a number of factors in its native environment contribute to natural regulation of its populations at a low level. These are both environmental factors like temperature conditions or limits on food supply, and biological factors. Biological factors include various types of natural enemies (predators, parasites, parasitoids or pathogens) that attack the insect either exclusively (in which case they are called specialist or host-specific natural enemies) or as one of a number of food sources (in which case they are called generalist natural enemies). In the absence of those regulatory factors in the insect's new environment, its population may increase considerably and it may become a serious pest. That is what happened when the Mexican bromeliad weevil entered Florida.

While that mixture of regulatory factors cannot be duplicated in the insect's new environment, the most practical and effective single factor that can be reproduced is that of specialist natural enemies. The host-specific natural enemies from the native homeland of the pest that have the greatest chance of surviving and regulating the pest population in its new environment are imported as biological control agents.

In some cases, biological control agents are better able to regulate the host population in the new place than in the homeland, because their own natural enemies are not imported with them, allowing them to achieve higher population densities. In other cases, however, introduced biological control agents do not adapt to the new environment and do not become established or fail to adequately regulate the pest population. Often, several biological control agents are used together to effect greater regulation.

The biological control agent that is imported is retained in a quarantine facility until it has been determined, through non-target testing (host range trials), that its release would not detrimentally affect native species. The importation and release of biological control agents is regulated to ensure the safety of people and the environment. In natural areas, where the use of chemical controls would be ecologically disruptive, the use of carefully screened biological control agents serves to protect biological diversity by affecting only the pest species.

If successful, classical biological control is a long-term solution. Once the pest's natural enemy becomes established in the area, further introductions are not needed. This type of biological control requires public funding, because it does not produce a marketable product, but after establishment of the biological control agent(s), continued intervention and monetary input are unnecessary. Although results are not immediate (it can take several years for the introduced agent to increase in population enough to effectively reduce the pest population and to spread throughout the pest's range), in a successful case of classical biological control, management of the pest population by the introduced agent continues indefinitely.

Since the idea is to copy a regulatory factor that in the pest's native environment maintains its population at a low level, the goal of classical biological control is not to eradicate the pest population, but to keep its numbers below unsatisfactory levels. In this case, we want to bring down the population of the Mexican bromeliad weevil enough so that its effects on bromeliad populations, particularly reproducing populations, are negligible. We can accept the presence of the weevil, as long as it does not threaten the continued existence of any bromeliad species, just as we do not consider the Florida bromeliad weevil to be a threat and accept its existence within the biota of bromeliads.

The goal of maintaining low populations of both the pest and the biological control agent highlights another advantage of using classical biological control in this situation, where additional related bromeliad pests may potentially enter the state at any time. If the Mexican bromeliad weevil were to be eradicated, the biological control agent would lose its food supply and therefore die out as well. However, if it were able to exist together with the pest weevil at very low population levels, it would continue to be present in the event another bromeliad weevil should immigrate to Florida. If that should happen, it may be able to regulate the population of the new weevil, depending on its degree of host-specificity. The biological control agent for the Mexican bromeliad weevil (Metamasius callizona) that we are currently working with was imported from Honduras, where it attacks the closely related species Metamasius quadrilineatus. M. quadrilineatus is the weevil most likely to gain entrance to Florida in the future, based on USDA-APHIS port interception records. In all, there are 14 species of Metamasius weevils not yet found in Florida that attack bromeliads in Mexico and Central and South America.

Classical biological control usually requires at least several years of research for successful exploration of natural enemies and introduction and establishment of a biological control agent. A great deal of time may be spent on non-target testing to ensure the safety of native species. Often at the start of a project there is little or no prior knowledge of the biology and ecological requirements of the pest or biological control agent.

Those implementing classical biological control must therefore deal with a variety of unknown factors, and there are no guarantees that the introduced biological control agent will become established and effectively regulate the pest population. About one-quarter of the insects introduced into Florida since 1890 as biological control agents against weed and insect pests have become established in the state, with a considerably higher percentage for biological control agents of weeds. However, despite the uncertainty of success, classical biological control remains our best means of reducing the impact of the widely distributed pest weevil in Florida's natural areas with minimal ecological disturbance. The chance of success would be higher if current funding levels for the project were maintained or increased.

In a case like that of the Mexican bromeliad weevil, the benefits of successful biological control in natural areas would extend to homeowners and private bromeliad collectors, who would receive the biological control services as the biological control agent naturally spreads throughout the pest's range. Commercial bromeliad nurseries may receive the benefits as well, depending on the degree of exposure of plants (shadehouses versus greenhouses) and the usage of pesticides in the nursery, which could exclude or kill the agent, respectively. However, the greatest benefit of successful management of the weevil would be shared by all Floridians and the tourists who visit the state's many bromeliad-adorned parks and natural areas.

• Bromeliad Weevil Research in Florida



• Steps to Manage the Weevil Through Classical Biological Control



• Lixophaga sp., Potential Biological Control Agent of the Mexican Bromeliad Weevil



• Progress Reports on Bromeliad Weevil Research