Gardening

Heavy rainfall & mosquitoes

By Dr. William M. Johnson, Galveston County Extension Agent - Horticulture

July 27, 2006

Mosquitoes prefer to rest in protected sites during the day. Area residents can take steps to help decrease populations of pesky mosquitoes.

Photo credit: William M. Johnson

Upcoming Program * Fall Vegetable Gardening * Saturday, July 29 9:00 - 11:30 a.m. Galveston County Extension Office, 5115 Highway 3, Dickinson Slide presentation on variety selection, soil preparation, establishment, general care and harvesting. No fee but reservation required (281-534-3413, Ext. 6 or GALV3@wt.net).

The frequent showers as well as heavy rains are a welcome contrast to drought conditions—that’s the good news. The not-so-good news is that the rains also provide attractive breeding sites for several species of mosquitoes and that mosquito populations typically start to significantly increase 7-10 days after a heavy rain.

A Cooperative Extension colleague at Purdue University in Indian once a mused that he estimated that mosquitoes cause one-fifth of all the profanity in the world! He proposed a quasi- scientific calculation while sitting in his backyard one evening with some friends. It was a beautiful evening, just about dusk. The temperature was perfect and there was no wind—ideal for a bar-b-que. He noted that suddenly the high-pitched drone of swarms of hungry mosquitoes could be heard approaching their picnic area. Then pandemonium struck and he was able to conduct his profanity experiment.

I suspect that the profanity level in Galveston County is a bit higher this year than last year—drought conditions can provide a bright side as mosquito levels were more tolerable in 2005. The bites of mosquitoes can be a real nuisance when one is trying to work in the garden or relax in the yard. We have about 30 species of mosquitoes that can occur in Galveston County and some can transmit serious illnesses.

Weather conditions this year have set the stage for our bumper crops of pesky and dangerous mosquitoes. The frequent rainfalls have flooded farmlands, filled ditches and low areas with stagnant water. Mosquitoes breed in stagnant water. A female mosquito (interestingly, only the females bite) that has taken a blood meal uses those nutrients to nourish up to two hundred eggs that she lays in stagnant water.

Depending on the temperature of the water, eggs may hatch in as few as 3 days. The resulting wrigglers can themselves complete immature development in as few as 10 days to become adult mosquitoes. The males fly off to feed on the nectar of tiny flowers but the female mosquito is immediately blood thirsty.

A female mosquito is a very effective search agent, zeroing in on hosts using temperature as well as carbon dioxide gradients to guide them. Once mosquitoes locate a potential host, they will persist until they are either successful in biting or become the target of a well-placed swat. Either way, the net result is often an addition of several colorful words in the victim’s vocabulary.

How can we help control these pests and help maintain a kinder English language? Knowing the basic requirements of developing mosquitos allows us to help manage their populations. Understanding the connection between water and mosquitoes is the key.

Professionals can monitor wetlands and drain or treat areas that are in need. However, a surprising number of mosquitoes develop right under our own noses. Thousands of mosquitoes can develop in your own back yard in a small forgotten container of water, discarded tire or clogged rain gutter.

Remember that mosquitoes can develop from egg to adult in as few as ten days. Anything that can hold water (from birdbaths to old buckets) is a potential breeding spot. These need to be emptied on a regular basis, discarded or adjusted such that they do not collect and hold water.

Homeowners should be aware that persistent pockets of stagnant water are more likely to become mosquito breeding grounds after heavy rains. Homeowners will likely be surprised at how many mosquitoes are homegrown in their own backyard and their neighbors’ backyards as mosquitoes typically do not travel far from their "birth place" if there is no need to do so.

It would be well worth the effort to make regular inspections of your property for likely mosquito breeding sites and keep in mind the following guidelines:

- Overturn or empty objects that have collected rainwater including standing water in saucers under potted plants.

- Clear gutters and down spouts of debris so that rainwater drains properly.

- Remove water that collects on sagging tarpaulins or other covers on your house or property.

- Eliminate standing water in tires, buckets, trash cans, etc.

- Empty and wash birdbaths weekly.

- Larger water-filled objects, such as water gardens that do not contain fish, can be treated with an insecticide containing the bacterium Bacillus thuringiensis israelensis (Bti), which does not harm fish, birds or mammals (including people).

- Discarded tires are a prime source of mosquito habitat because they cannot easily be drained.

- On one occasion, I saw a half-dozen mosquito wigglers or larvae in a clear vase of an indoor fresh flower arrangement! Just remember that still water is the key item.

Understanding the water/mosquito connection and taking steps to decrease these potential mosquito breeding sites will go a long way in saving outdoor recreation events. We look to our County Mosquito Control District to provide widespread control of mosquito populations. The County Mosquito Control District staff has been diligently addressing the gazillion mosquitoes but they are not magicians. If everyone gets on this bandwagon, we will also help preserve our English language in its more pure form!

Dr. Johnson is a horticulturist with the Galveston County
Extension Office of Texas Cooperative Extension, Texas A&M University. Visit his web site at http://aggie-horticulture.tamu.edu/galveston/index.htm

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