Chemical Insecticides
Adult Wyeomyia mosquitoes fly during daylight hours. They are not affected by insecticidal fogging conducted at dusk and after dark by mosquito control districts against pest mosquitoes in general, and are not even affected by experimental fogging in daylight (3).
In general, reliance on chemical pesticides to kill Wyeomyia mosquito larvae is a poor control strategy. Introduction of chemical pesticides into bromeliad tanks will kill Wyeomyia (and other) larvae and provide temporary relief from the adult mosquitoes that would develop. When the larvae are killed by pesticides, food accumulates, uneaten, in bromeliad tanks until the breakdown of the pesticides. At that time, Wyeomyia (and other) larvae newly hatched from eggs have an abundant food supply, and they can develop rapidly with little or no mortality from starvation, producing adults that are larger than normal. These larger adults are capable of producing more eggs than the typical small adults, so the population size returns to normal in short order.
The only effective chemical control is obtained by repeatedly applying chemicals, causing, in effect a chemical treadmill, at high cost of labor and pesticides. Some improvement may be found in use of slow-release chemicals carried on inert substances, but labor costs are still considerably higher than in application of chemicals in large bodies of water such as ponds and ditches, and the consequence still leads to the resurgence of Wyeomyia numbers after the treatment cycle stops. Such treatments also provide opportunity for the development of Wyeomyia (and other) larvae that are genetically resistant to chemicals. Chemical insecticides applied against scale insects and other pests of bromeliads probably will affect Wyeomyia (and other) larvae because the chemicals will get into the bromeliad leaf axils; if the pesticides are applied at high enough concentration the larvae will die, otherwise these applications may contribute to development of resistance.
Microbial Insecticides
Spore-forming bacteria of the genus Bacillus have been developed as microbial insecticides against mosquito larvae, which the bacteria kill by releasing toxins. Bacillus sphaericus offers advantages over Bacillus thuringiensis israelensis in that it can reproduce in larvae of some mosquito species, and can persist in some aquatic environments for several weeks (29). Laboratory tests showed pathogenicity of Bacillus sphaericus strain 1593 against Wyeomyia mitchellii but not against chironomid midge larvae (1); Bacillus thuringiensis israelensis did not exhibit a pathogenicity against Wyeomyia vanduzeei (2). Bacillus sphaericus strain 1593, sprayed experimentally at 10 spores/ml against Wyeomyia larvae in tank bromeliads, suppressed Wyeomyia populations for up to two months (30). Further field tests of Bacillus sphaericus against Wyeomyia larvae also gave promising results (35).
This microbial insecticide may perhaps be safe to non-target chironomid midge larvae in bromeliad tanks. If so, this selective effect would be beneficial not only because the midge larvae are harmless but also because they may reduce nutrients in bromeliad tanks. Unfortunately, no U.S. company is yet marketing Bacillus sphaericus for this purpose; a large company which investigated the possibility concluded that the potential market was too small to bother with. More recently, however, B. sphaericus is being produced and marketed in Brazil, and there is no good reason why it should not be imported into Florida.
Unfortunately, no strain of Bacillus sphaericus has been found effective against Aedes albopictus larvae. If Bacillus sphaericus were now applied in bromeliads in southern Florida it might allow an increase in numbers of Aedes albopictus by suppressing Wyeomyia larvae. A microbial pesticide suitable for use against Aedes albopictus is needed urgently.
Management
With rare exceptions, larvae of the two Wyeomyia species have been found only in bromeliad tanks. The numbers of these mosquitoes in any given area depend primarily on the number of tank bromeliads in that area, secondarily on the nutrient supply in the bromeliad tanks. Reduction in the number of tank bromeliads will cause a corresponding reduction in the number of Wyeomyia. An effective method of controlling Wyeomyia is to limit the number of bromeliads, and this is a viable option for people who have neither an interest in bromeliads nor the time to maintain them.
For people who have a real interest in bromeliads, and time to care for them, there are alternatives. If the number of Wyeomyia larvae developing depends on the food supply in bromeliad tanks, a reduction in the food supply will cause a reduction in the number of larvae developing. In general, bromeliads grown in glasshouses and shade houses will not receive dead tree leaves and twigs, which form the basis of the food chain on which the mosquito larvae feed. Thus, fewer Wyeomyia should develop under those conditions.
If bromeliads have to be grown under the shade of trees for lack of other shaded sites, then removal of fallen leaves and twigs from the bromeliad tanks should reduce the food available to the mosquito larvae. Pressure from a garden hose with appropriate nozzle can be used to flush the majority of Wyeomyia eggs out of tanks of bromeliads growing on the ground (18) and may be expected to flush out nutrients available to Wyeomyia larvae. This method should be used frequently to cause much suppression of adult mosquito production. Bromeliad tanks can be provided with artificial fertilizers to compensate for natural organic materials removed. Such fertilizers do not provide food for mosquito larvae.
Successful biological control methods against Wyeomyia might eliminate need for any other control method. Integrated pest management for Wyeomyia would use management methods in conjunction with biological control methods. Some research into biological control methods for Wyeomyia has been conducted as described below, but has not yet been brought to a satisfactory conclusion and, as of this writing, there is no research program leading to that objective.
