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Written by Jeff Shimonski, BT Contributor   
June 2020

Mosquito hatcheries are often manmade

I Pix_YourGarden_6-20was working in downtown Miami early one morning last month along NE 1st Avenue, inspecting a group of trees, when I sat down on a bench to write up some notes. Now when I work, I wear thick pants and a thick shirt to avoid getting scratched up by the vegetation or bitten by aggressive insects, but immediately I was being bitten and assailed by a swarm of mosquitoes.

They looked like Culex species, but I wasn’t concerned with identification at the time. I wanted to complete my project, and I had other issues -- my face mask kept fogging up my glasses.

Ironically, my May column (“Mosquito Season Is Here”) was on the mosquito larvae control program I used at Jungle Island, but it hadn’t come out yet.

When my note taking was complete, I began to walk back to my car. I also wanted to get away from the mosquitoes.

Where were these mosquitoes coming from? Where were they breeding? I was in the middle of our concrete-covered city. There were no natural bodies of water within half a mile. There are no swampy areas nearby, and there are no dense plantings of areca palms that some people have told me cause mosquitoes to breed. (I mention the areca palm issue because I’ve been yelled at and schooled by “experts” who said, “Remove the areca palms and the mosquitoes will stop breeding here.” So much for science and basic biology.

It was also windy, and I’m sure you know when you walk past large buildings that the wind can be ferocious at times. Mosquitoes are generally not great flyers and don’t travel large distances on their own, but they can get blown around.

The area I’d just walked through was about three city blocks in size -- all very large new buildings or recently graded new construction sites. There was the token landscape thrown in here and there. I’d just inspected one, and it had no mosquito breeding sites. Yet as I walked around, whenever I stopped out of the wind, mosquitoes found me.

The situation reminded me of my mosquito larvae control project at Jungle Island. The mosquito issue there was manmade. At the park and on Watson Island, the vast majority of mosquitoes were breeding in the storm drains, not so much in the bromeliads. I knew this from the thousands of water samples my interns and I had taken from the axils of bromeliads leaves, and from the storm drains onsite.

I suspect this is the same issue in downtown Miami, though it’s actually an issue everywhere. I have watched mosquitoes flying out of floor drains to bite people (and me) in outdoor patios in fancy retail areas.

I have written before about messy property owners who leave water to collect on their properties for mosquitoes to breed in; this is definitely not an issue related to income or to specific neighborhoods.

The photo that accompanies this article is of a red heliconia inflorescence. The things shaped like big red boats are called bracts, and individual flowers emerge from inside of them. The bracts will also accumulate water, and in the New World tropics, where 99 percent of all heliconia species are from, certain species of mosquitoes will breed in them. I have sampled thousands of heliconia bracts here in south Florida over the years, and have never found mosquito larvae inside them. We don’t seem to have those mosquitoes here yet.

I once found a particularly small area at the park that suffered from swarms of biting mosquitoes. These were Aedes aegypti, a very serious disease vector. I couldn’t understand where they were coming from since we had achieved control in our storm drains and in our bromeliad collection.

Then I looked up into the canopy of the closest tree, a sausage tree.

I put a ladder into the canopy and climbed into the tree. There it was, a small cavity filled with water and mosquito larvae. I collected the larvae and identified them as Aedes aegypti, the ones that had been biting me. I treated the water inside with a granular form of Bacillus thuringiensis, a bacterial product that is not harmful to mammals or birds.

A week later I checked the water, and no mosquito larvae. The problem was that we’d need a ladder to check and treat the cavity, so I came up with an idea to use utility foam to spray into the cavity and displace the water. That way I wouldn’t have to inspect and treat the water inside the cavity, and there would be no mosquito larvae. It worked for the final three years that I was at the park.

 

Jeff Shimonski is an ISA-certified arborist municipal specialist, retired director of horticulture at Parrot Jungle and Jungle Island. Contact him at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

 

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