Here’s how to enjoy bromeliads without the biting bugs

Although I’m a generalist when it comes to plant selection for landscaping, there are a few plant groups I always like to feature. One is the bromeliad family. I’ve written about various cousins of these pineapple relatives many times, but what provokes me now is the beautiful show of red color that a bed of Portea petropolitana (variety rubra) has put on display at Jungle Island, where I work.

The genus Portea has a number of very attractive species within it. Many grow well in full sun, forming dense beds that will bloom twice a year if there are enough plants. Remember, most bromeliad species bloom only once and then die, usually after forming a number of “pups” or offshoots. A large, well-established bed of bromeliads with a hundred or so plants will not only bloom twice a year, but each blooming period can last a month or two.

I’ve grown the aforementioned bromeliad for years. I’ve also grown with much success several of its close relatives -- Portea kermesina, P. petropolitana (variety extensa) and P. leptantha. These bromeliads will grow well in large containers, but I prefer them on the ground. They will also grow as epiphytes (in trees). If you’re very color-conscious, the hues of the inflorescences will be brilliant in full sun but the foliage will be a very light green color. The foliage will become a darker green in a bit of shade, thus making the inflorescence’s contrast even greater.
Certain species of mosquito will breed in the leaf axils of bromeliads when they contain water. My work with mosquito-larvae control has taught me that even bromeliads with very narrow leaves and only a very small amount of water in the leaf axils (like some of the Porteas) will have mosquitoes breeding in them, blazing sun notwithstanding. A few granules of Bacillus thuringiensis (variety israelensis) or Bacillus sphaericus in each leaf axil will normally kill mosquito larvae within 24 hours and continue doing so for two to three weeks. Bacillus is a bacteria, and these mentioned are nontoxic to mammals, birds, reptiles, and most other insects. They are considered “bio-rational” pesticides.

Bacillus thuringiensis (variety israelensis) can be purchased in granular form from a number of online sources. To apply it, I use a plastic jug with a handle (windshield-washing fluid, bleach, or something similar). I drill numerous holes in the jug’s bottom, each a bit larger than the size of the granules. I then pour in a few ounces of the product and shake over the bromeliads. The granules roll naturally into the leaf axils. Over time, it’s important to use different products to avoid eventual insect resistance. I’ve been doing this successfully at Jungle Island for the past three years. We no longer need to spray for mosquitoes.

Speaking of mosquitoes, recently I was asked to conduct a mosquito survey on a couple of very large properties in Miami. As I explained to the property managers, there are about 65 species of mosquitoes that have been documented in Miami-Dade County, but only a handful of them are native. Some of the exotic species are notorious disease vectors, carrying yellow fever, dengue, malaria, West Nile virus, and encephalitis. I proceeded to inspect the properties, and after a few hours was able to collect dozens of mosquito larvae from bromeliads, tree cavities, water features, bird baths, and discarded debris that contained rain or irrigation water. I spent the next week identifying the larvae.

I found close to ten species! Only two of them were native; the others were known disease vectors and aggressive biters. Here are some things that you should know about these unwelcome creatures. Lots of rain does not cause mosquitoes to breed. It’s when that rain or irrigation water collects in a container that the mosquitoes have a place to breed. Sometimes it takes less than an ounce of water. Dumping out the water (like in a bird bath) may kill the larvae but will not remove the eggs from the sides of the container if they belong to a species of mosquito that lays its eggs above the water line. These eggs can remain viable and dry for more than a year. That’s why there are so many mosquitoes after flooding rains. Clean that container with soap!

If you collect rain water in a water catchment for irrigation use, you’re doing something really smart. Now make sure that you screen off the container completely so mosquitoes don’t lay eggs in the water or right above it. Also make sure that you screen off the pipes that channel the rainwater to the catchment. I have seen adult mosquitoes fly through a two-inch pipe more than 200 feet from a covered storm drain into a building through a drain on the floor. Don’t underestimate these insects!

Some of the more serious disease-carrying mosquitoes, like Aedes aegypti and A. albopictus, breed in small containers, and especially tree holes. I have found that many radically pruned trees end up with rotten holes in them. Water collects in these hole, and so do mosquito larvae. It’s very important to prune properly, and equally important to search for such holes in a tree if you’re serious about mosquito control. I use utility foam to fill the holes.

Jeff Shimonski is an ISA-certified municipal arborist, director of horticulture at Jungle Island, and principal of Tropical Designs of Florida. Contact him by e-mail at This e-mail address is being protected from spambots. You need JavaScript enabled to view it , or visit tropicaldesigns.com.

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