BOLL WEEVIL, COTTON. The first home of the cotton boll weevil was undoubtedly in the plateau region of Mexico or Central America. Before 1892 it had spread throughout the larger portion of Mexico. It occurs southward to Guatemala and Costa Rica, and in the east half of Cuba. About 1892 it crossed the Rio Grande near Brownsville, Texas, and entered U.S. territory. By 1894 it had spread to half a dozen counties in southern Texas, and since has extended its range annually until in 1928, almost all of the most important cotton-producing sections had become infested. Practically the only territory remaining uninfested was the semi-arid zone along the western margin of the cotton belt. The 192i estimate of the U.S. department of agriculture of the potential production of cotton prevented by weevils was 6,277,000 bales.
The adult boll weevil is about 3- in. long, varying from to in., with a breadth about one-third of its length. This measurement includes the snout, which is approximately half the length of the body. Variation in size is due to the amount of food the insect has obtained in the larval stage. Individuals from bolls (unripe pods containing lint and seed) are therefore nearly always larger than those from squares (fruit buds). Recently emerged individ uals are light yellowish in colour, but this changes to a grey or nearly black shade in a few weeks' time. In the field, the most conspicuous indication of the presence of the boll weevil is the flaring and falling of numbers of squares or buds. Unfavourable climatic conditions and careless cultivation, however, frequently cause great shedding of the fruit, which is often mistaken for weevil damage. If excessive shedding be noted and the squares upon being cut open show a white, curved grub that has fed upon the contents, there is little doubt that the boll weevil is the insect causing the damage.
The boll weevil passes the winter as an adult or beetle. With the advent of autumn weather the adult boll weevils in cotton fields begin to seek protection against the winter. They fly in every direction, although their movements are governed partially by the prevailing winds. They may fly into hedges, woods, corn fields, haystacks, farm buildings or other places. A number of weevils also obtain hibernating quarters without leaving the cotton-fields. These may crawl into cracks in the ground, under grass, weeds or other trash, and into the burs from which the cotton has been picked. During the winter the weevils take no food, and remain practically dormant; on warm days they may move about to a certain extent. Emergence from hibernation depends primarily upon temperature and rainfall in the spring, although some minor factors are concerned. In the southern portions of the cotton belt emergence usually begins from the first to the middle of March, but farther north it is somewhat later. Emergence has been prolonged from the middle of March to June 28, and in more extreme cases from the middle of Feb ruary to about the first of July.
In the spring and throughout the fruiting season of cotton, the eggs are deposited by the female weevils in cavities formed by eating into the buds and fruit of the plant. An egg hatches under normal conditions in about three days, and the grub immediately begins to feed. In from 7 to 12 days the larva or grub passes into its pupal stage, corresponding to the cocoon of butterflies and moths. This stage lasts from three to five days. Then the adult issues, and in about five days begins to breed. Climatic conditions cause considerable variation in the duration of the stages, but on an average it requires from two to three weeks for the weevil to develop from the egg to the adult. The males feed upon the squares and bolls without moving until the food begins to deteriorate. The females refrain, throughout most of the season, from depositing eggs in squares visited by other females, but late in the autumn, when all of the fruit has become infested, several eggs may be placed in a single square or boll. As many as 15 larvae have been found in a boll. The squares are greatly preferred as food and as places for depositing eggs. As long as a large supply of squares is present the bolls are not generally damaged to any serious extent. The bolls, therefore, have a fair chance to develop as long as squares are being formed. The weevil, so far as at present known, breeds in no plants other than cotton and a wild plant related to cotton found in the mountains of Arizona.
In spite of the many complexities involved in the problem of weevil control, efficient methods (see COTTON) have been devel oped for reducing its damage, which are of practical use to growers. These are described in Farmers' Bulletin 'No. 1329, pro curable on request from the U.S. department of agriculture, Washington, D.C. (B. R. C.)