N. G. COBBETT AND R. C. BUSHLAND.
THE HOG LOUSE, Haematopinus suis, is a bloodsucking parasite. It is the largest of the lice that prey on domestic animals. The full-grown female often attains a length of one-fourth inch. The males are slightly smaller.
The lice are easily seen on swine. They are brownish gray and have a Peculiar habit of traveling sidewise over the skin and through the bristles.
They are parasitic on swine only and pass their entire life cycle on the host.
Hog lice may attack swine of any age or condition. They infest both domesticated and wild hogs in practically all parts of the world. Hog growers generally recognize them as a pest responsible for considerable losses to the swine industry.
The lice feed frequently. They puncture the skin and suck blood in a different place at each feeding. Each puncture produces irritation and itching, which cause the infested hogs to rub themselves vigorously against any available object.
The frequent scratching and rubbing destroy the hair in patches and often wound the skin. The lice congregate around the abrasions and cause further irritation. As the lice increase in numbers, the infested animals suffer constant irritation. They are restless and do not eat properly. They become unthrifty and do not grow or gain weight normally. Young animals especially suffer a lowering of vitality so that they may be more susceptible to attack by other parasites and to contagious diseases.
The female louse attaches her yellowish-white eggs to the bristles of the hog, usually in or around the ears and on the neck, shoulders, and flanks. She lays 3 to 6 eggs daily and an average total of 90 eggs during her life span, which is about 35 days. The eggs hatch in 12 to 20 days. The eggs farthest out on the bristles away from the body warmth usually hatch last.
After emerging from the egg, the nearly colorless, young louse becomes active. It seeks the tender skin nearest the point of its emergence and begins feeding. Clusters of young lice are often found inside the ears, in the region of the armpit and flank, and on the belly of infested swine. The young lice become sexually mature in about 10 days. The females may begin laying eggs when they are 12 days old.
The lice transfer readily from one hog to another when the animals are in close contact. Since it is the habit of swine to rest and sleep closely together, the lice spread rapidly in a herd and suckling pigs soon acquire them from their infested mothers.
Because hog lice live only a few days when separated from swine, enclosures, trucks, and cars in which infested swine have been are seldom a source of infestation if left unoccupied for several days.
Oils and medicated liquids are usually used against hog lice. They are best applied as dips or sprays or in well-constructed and maintained hog wallows. Used in hog oilers or applied by hand, the remedies will usually reduce and hold the lice infestation in check but seldom eliminate them entirely because it is hard to get a thorough coverage of all infested animals with them.
Crude petroleum and oils derived from crude petroleum are economical and commonly used and are preferable for use in hog wallows.
Coal tar-creosote preparations, properly used in soft water, are also effective, but they have been largely replaced by BHC, lindane, DDT, chlordane, and toxaphene, all of which are available as wettable powders or oil emulsions.
Dips and sprays made up with BHC or lindane should contain 0.06 percent of the gamma isomer the insecticidal ingredient when they are used for hog lice. The DDT dips or sprays should contain 0.75 percent of DDT. Those made up with chlordane or toxaphene should contain o.5 percent of either chemical.
These chlorinated hydrocarbon insecticides will kill all the lice present on the swine. They also remain active on the bodies of treated animals long enough to kill most of the young lice that hatch after treatment, and they destroy some of the lice eggs. Nevertheless, a few eggs and late-hatching lice may survive a single dipping or spraying, and a second treatment in 10 to 14 days should be applied.
In treating swine for lice, it is important that all the body surfaces, including the inside of the ears, be thoroughly covered with the remedy and that all animals in the herd are treated.
N. G. COBBETT joined the Department of Agriculture soon after he was graduated from Colorado Agricultural and Mechanical College in 1921.
R. C. BUSHLAND is in charge of the Kerrville, Tex., laboratory of the section of Insects Affecting Man and Animals, Entomology Research Branch.