September 2003

Bromeliads and Mosquitoes

            First of all, what are bromeliads? Bromeliads, commonly called air plants, are in the family Bromeliaceae which consists of over 2,500 species. Pineapples and spanish moss are well known species in the bromeliad family. Most bromeliads are native to South and Central America, only 16 species are native to Florida.

            Tank bromeliads, species of bromeliads that hold water in their leaf axils, thus the name “tank”, are the bromeliads certain species of mosquitoes have evolved with over the eons of time. Tank bromeliads are popular in central and south Florida and are becoming more common throughout the rest of the state. The reason for their popularity is because of their colorful flowers, attractive foliage, require a minimum amount of care, and grow best in partial or full shade. The tank bromeliads obtain their nutrients from decomposing material (leaves, insects and twigs) that fall into the water-filled “tanks” of the plant. This decomposing organic matter and water also attracts mosquitoes as a place to lay their eggs. Larvae of over 200 different mosquito species have been found in the water held in the tanks of bromeliads in the neotropics. In Florida only 2 native mosquito species are specific to and specialized for existence in tank bromeliads, Wyeomyia vanduzeei and Wyeomyia mitchellii. Adults of these mosquitoes are among the smallest mosquitoes in Florida, light tan in color, blood feed in the late afternoon, prefer shaded locations and do not fly far from the bromeliads they depend on. Females of these Wyeomyia species lay their eggs during daylight hours by hovering over bromeliad tanks and dropping their eggs, one by one, hopefully into the water being held by the bromeliad. If the egg doesn’t land on the water and falls onto a dry surface, the egg can stay stranded and viable for over 3 weeks until washed into a plant’s tank by rainfall. The maximum life span of the adult mosquitoes is about 3 weeks. These two Wyeomyia species are not known to vector any diseases to humans. Because of this, Wyeomyia vanduzeei and Wyeomyia mitchellii are considered simply as pests of man, or more accurately, persistent pests, as long as the tank bromeliads are around.

            The solution to the nuisance that these mosquitoes cause is simple, get rid of the bromeliads. However, unlike other containers around the home that collect water, these “containers” are alive, pretty, and you probably spent money to purchase them. Bromeliad cultivation is popular. The Bromeliad Society International (BSI), which publishes The Bromeliad Society Journal, was formed in 1951. The cultivation of these plants has become so popular that there are now 11 local bromeliad societies in Florida alone. So how do you keep the bromeliads without the mosquitoes? Chemical control with a pesticide applied to the water held by the plant is effective but must be repeated on a weekly basis, which eventually results in a high cost for labor and pesticides. Another strategy is to raise the plants in glass houses or areas that keep organic matter from falling into the tanks of the plants. Keeping organic matter out of the plants takes away the nutrients that attracts the female mosquitoes and stimulates them to lay their eggs. Without sufficient nutrients the water just isn’t good larval habitat for mosquitoes of any specie. However, here again glass houses are an added expense. The method that works well, with minimal expense and effort, is to spray the bromeliads once a week with a light mineral oil that doesn’t harm the plants. These oils can be obtained at almost any local nursery. The oil forms a layer over the water and will suffocate any larva that are residing in the plant. The key to this method is to do it regularly and thoroughly so that every bromeliad is treated. If all this seems to be too much and the nuisance from the mosquitoes they produce is unbearable, then the simple solution is to destroy the bromeliads. Without these plants the Wyeomyia species cannot exist.