Gardening Tips: October 5, 2011
It is raining as I write this column, an all too common occurrence since August 28 when Irene arrived. All told, I have measured more than 25 inches of rain at my home since that fateful day that changed the landscape of our region. The clean-up efforts will continue for years and the side effects of all this rain are being felt right now as we deal with an explosion of mosquitoes.
There are over 2,500 species of mosquitoes in the world with 150 or so in the United States. In the Hudson Valley/Catskill region we have only a few to contend with but they certainly can make life miserable. They can also be deadly, transmitting serious diseases to humans and other animals.
Albany just recorded its first case ever of West Nile Virus, a potentially deadly, flu like illness, which presents the greatest risk to the elderly.
Join the club
It is funny that for the first time I just realized that I am now a member of that club, known as “the elderly.” I don’t think I like that designation.
The mosquito goes through four separate and distinct stages of its life cycle and they are as follows: Egg, Larva, pupa, and adult. Each of these stages can be easily recognized by their special appearance. All mosquitoes must have water in which to complete their life cycle. This water can range in quality from melted snow water to sewage effluent and it can be in any container imaginable. The type of water in which the mosquito larvae is found can be an aid to the identification of which species it may be.
Also, the adult mosquitoes show a very distinct preference for the types of sources in which to lay their eggs. They lay their eggs in such places such as tree holes that periodically hold water, tide water pools in marshes, sewage effluent ponds, irrigated pastures, rain water ponds, etc. Each species therefore has unique environmental requirement but all need water. Eggs are laid in water or on damp soil that will be flooded by water. The eggs are laid either in clumps called “rafts” or singly. Most eggs hatch within 48 hours and turn into larvae.
The larva live in the water and come to the surface to breathe. They shed their skin four times growing larger after each molting. At this stage they can be easily recognized by using a white colored cup or ladle to scoop up a water sample. They are also called “wigglers” at this stage. Most larvae have siphon tubes for breathing and they hang from the water surface. The larva feed on micro-organisms and organic matter in the water. On the fourth molt the larva changes into a pupa.
The pupal stage is a non-feeding stage when the mosquito turns into an adult. It takes about two days before the adult is fully developed. When development is complete, the pupal skin splits and the mosquito emerges as an adult. The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and all its parts to harden. Also, the wings have to spread out and dry properly before it can fly. Some species can complete their entire life cycle in as little as four days. Only adult female mosquitoes feed on blood; the males feed on plant juices.
Mosquito management involves draining any sort of standing water from tires, to tree cavities to gutters, kiddie pools, puddles, ditches etc. Mosquitoes are not strong flyers and most of those that attack you probably hatched from within 100 yards of where you are standing. Ponds that hold fish or amphibians are usually mosquito free because these animals feed on the larvae. Bats are the major predators of adult mosquitoes and a single bat may eat thousands of them in one night.
Repellents containing DEET are usually very effective as are some herbal remedies and even some cosmetics, but all repellents must be renewed periodically. Be sure to follow the label directions when using any repellents, especially when using them on young children.
There is a very safe and effective product that kills mosquitoes in the larval stage. It is a naturally occurring bacteria, called Bt, variety israeliensis and it is sold in donut shaped packages called “Mosquito dunks.” I use these in the 55-gallon drums that I store rainwater in for irrigating my garden.
I have also used them, broken up and scattered on periodic wet spots or areas with standing water after heavy rain. There is no such thing as a pesticide that only kills one species of insect but these mosquito dunks only kill mosquito and fly larvae without affecting other types of insects or other animals for that matter.
Some of us have had a light frost already but it will take several days of temperatures in the mid-20s to end the current mosquito outbreak.