Mosquitoes on Livestock and Man

ARTHUR W. LINDQUIST AND WILLIAM C. MCDUFFIE.

WE THINK of mosquitoes primarily as scourges of mankind. They cause discomfort and irritation. They may keep us from developing industrial, agricultural, and recreational areas.

They may transmit appalling diseases filariasis, yellow fever, encephalitis, and malaria.

Mosquitoes also attack livestock. They can transmit encephalomyelitis, anaplasmosis, swamp fever, fowlpox, and other diseases to animals. Mosquitoes irritate cattle and cause them to mill around, stamp, and swing their heads in efforts to fight off the insects.

That and loss of blood from bites cause losses in weight and milk production. Livestock have been killed by swarms of mosquitoes.

About 145 species of mosquitoes exist in the 'United States. Some are localized and of little economic importance. Others are widespread.

The species vary in their habits, but all have a common characteristic the larvae develop only in water. But not all species breed in all types of water.

Some prefer fresh water and cannot tolerate alkaline, highly acid, or polluted water. Others prefer brackish water in salt marshes or in tree holes.

Some develop in fresh, alkaline, or polluted water. Larvae do not breed in rapidly flowing streams, canals, or irrigation ditches, but they may be present in quiet backwaters of streams or in vegetation-choked channels.

To CONTROL mosquitoes, one has to know the places where larvae are breeding and the adult habits.

Some of the main breeding areas and species are:

Temporary rain pools: Aedes atlanticus, A. vexans, A. infirmatus, A. canadensis, Psorophora confinnis.

Flooded areas: A. sticticus, A. vexans, A. dorsalis.

Irrigated pastures: A. nigromaculis, A. dorsalis, Culex tarsalis.

Salt marshes: A. sollicitans, A. taeniorhynchus, A. squamiger.

Standing water around houses: A. aegypti, C. quinquefasciatus, C. pipiens.

All mosquitoes have four stages in their life development eggs, larvae, pupae, and adults. Most of the mosquitoes of the Aedes group lay their eggs on the ground after the water has receded.

Culex and Culiseta lay their eggs in rafts on the surface of the water.

Anopheles lay theirs singly on the water surface.

Aedes and Psorophora species over-winter in the egg stage (except A. varipa1pus, which overwinters either as eggs or larvae).

Anopheles and Culex mosquitoes generally overwinter as adults and can be found in such protected places as cellars, caves, culverts, and buildings.

Mansonia overwinter as larvae attached to roots of aquatic plants.

Some species fly 10 to 15 miles or more from the point of origin. Culex, Culiseta, and Anopheles seldom fly more than a mile or two.

The number of generations of mosquitoes varies with the species and the type of climate the Culex and Anopheles and many of the Aedes have several generations each year. Other Aedes, such as the snow-water species, usually have only one generation a year.

YOU CAN END the annoyance of mosquitoes by directly controlling larvae and adults or by applying protective treatments to animals.

Direct control means filling or draining the breeding places or applying chemicals to larval breeding sites or areas infected by adults. Since mosquitoes may fly some distance, community action in eliminating breeding areas and applying insecticides offers the best method of control. Lacking that, protective applications of insecticides and repellents to animals must be made.

If a control program is to be successful, surveys must be made to determine where mosquitoes are breeding and what species are involved. To locate mosquito larvae, a search must be made in every water area in the locality ponds, ditches,swamps, overflows, seepages, and containers such as wells, cisterns, cans, jars, and discarded auto tires. An ordinary water dipper may be used for taking water samples. Ten to twenty dips near the edges of a pond are usually necessary. A close examination of the water in the dipper will reveal the wrigglers (larvae).

IRRIGATED PASTURES and meadows frequently produce myriads of mosquitoes when water is allowed to stand on the land for 5 to 8 days. Irrigation in the United States has created serious new mosquito problems.

To curtail the breeding of mosquitoes in pastures, the land must be prepared properly for irrigation and for the removal of excess water. Water should be used only as needed. Overirrigation should be avoided. Animals should be taken from pasture when the soil is wet. Trampling of the soil by farm animals reduces the penetration of water into the earth and forms small depressions, which hold water long enough to produce mosquitoes. The stock should graze fields in rotation. Those practices reduce mosquito breeding and increase crop production. Groups of farmers can do much to control mosquitoes by following the proper irrigation and pasturing practices.

On the farm and in suburban areas, septic tanks and cesspools may produce hordes of mosquitoes. Drains from septic tanks should lead to a properly constructed drainage field, where the fluid will enter into the soil. Cesspools should be tightly covered.

Dairy drains may be sources of mosquitoes. The liquid can be applied to fields, and collected water can be pumped into the irrigation system. Keeping weeds from growing in the dairy drain pond also reduces mosquito breeding.