A potential biological control agent for the weevil has been found in Honduras, an undescribed fly species in the genus Lixophaga (Family Tachinidae). It was formerly thought to be in the genus Admontia. Ron Cave found this specialist parasitoid fly attacking the closely related weevil species Metamasius quadrilineatus in bromeliads in a Honduran cloud forest. During 1996-1997, Diego Alvarez, a student at El Zamorano, studied the biology of the Lixophaga sp. fly as part of his thesis research, entitled "Reproductive Biology and Laboratory Rearing Methods of Lixophaga sp. (Diptera: Tachinidae), parasitoid of Metamasius quadrilineatus Champion (Coleoptera: Curculionidae)". Additional observations have been made in Florida during attempts to establish a colony of this fly in quarantine.

The fly attacks the larval (immature) stage of the weevil. Adult female flies larviposit (lay larvae instead of eggs) on the bromeliads at the entrance to weevil tunnels. The fly larvae (maggots) seek out and parasitize the weevil larvae within the tunnels they make in the base of the host plant. The fly maggots must be able to find the weevil larvae within a short period of time, and humidity must be high enough within the weevil tunnel, because the fly maggots are susceptible to drying out during this time. Up to four fly maggots have been observed to emerge from a single weevil larva, but when multiple flies develop in a weevil larva, some or all become small and unhealthy adults as a result of inadequate nutrition.

Under laboratory conditions, the larval stage of the Lixophaga sp. fly was determined to average 18-22 days. When fully developed, the fly larva emerges from the weevil larva and pupates (changes into a pupa, the stage before the adult stage) close to the weevil larva, which dies as a result of the fly larva's emergence. The fly spends the non-active pupal stage within a hard, protective puparium. Fly larvae may leave the weevil larva after the weevil has formed its own protective cocoon in preparation for its pupation. Fly puparia may therefore be found either within the weevil's cocoon or within the stem and leaf tissue close to the newly-killed weevil larva.

After an average of 20-22 days in the pupal stage, the adult flies emerge. They mate during their first few days and females are able to larviposit within two weeks. Adult flies given a choice of healthy bromeliads, weevil-damaged bromeliads, or weevil-damaged bromeliads containing weevil larvae visited damaged and weevil-infested plants significantly more than they visited healthy bromeliads. Typically, parasitoids like the Lixophaga fly search for their hosts (the weevil in this case) by first finding the plant upon which the host feeds. To find plants likely to contain their host, they use chemical cues given off by insect-damaged plants, sometimes together with chemicals emitted from the insect's saliva or frass.

As a result, the fly is unable to successfully find the weevil host larvae when they are openly presented to it. It can only parasitize the weevil host when it is inside a damaged bromeliad. In the fly's cloud forest habitat, percent parasitism of weevil larvae hosts varies by season but has been found to reach 60% in some areas. Highest rates of parasitism have been observed between July and November.

The fly was imported into Florida as part of the biological control program to manage the Mexican bromeliad weevil (Metamasius callizona). It has been found to attack the Mexican bromeliad weevil in Tillandsia utriculata plants at the Florida Department of Agriculture and Consumer Services, Division of Plant Industry's quarantine facility in Gainesville.

If results of host range tests show that the fly does not attack any species other than bromeliad-killing Metamasius weevils, then an application for a release permit will be submitted. If approved, it will allow the fly to be removed from quarantine to be reared and released in nature. Non-target testing begins with the species most closely related to the target pest species. Only two other species of Metamasius weevils are found in Florida, Metamasius hemipterus and Metamasius mosieri. If the fly attacks neither of these, there would be no need for further testing, because it will not attack less related species. However, if it does attack one or both of the other Metamasius species in Florida, additional host testing may be necessary.

To ensure that the biological control agent will find enough weevil hosts in which to reproduce and will be able to disperse adequately, releases must be made in areas where the weevil is found in abundance and where the bromeliad habitat is not so isolated that it prevents dispersion of the fly to surrounding areas. Selected state parks will be targeted for initial releases once a release permit is approved. Field studies are underway to determine the most appropriate locations and seasonal timing of releases.