Insect identification > Coleoptera > Rhynchophora > Boll weevil

Boll weevil

The boll weevil (Anthonomus grandis Boh.). - This is one of the most serious insect pests of cotton. Recent estimates place the destruction of cotton by this insect at about millions of bales a year, besides all the indirect loss to all lines of business connected with the crop.

The boll weevil is a native of tropical America, whence it spread northward and entered Texas about 1902. Since then it has continued its spread and is now present practically everywhere in the cotton belt.

The adult boll weevil varies considerably in size but averages about a quarter of an inch in length. When it first emerges from the pupa it is light brown, but it soon becomes gray or almost black. It winters as the adult, hiding under rubbish, in cracks in the ground, in Spanish moss growing on the trees or in fact in any protected place, though those which winter in the cotton fields appear to be least protected and hence least liable to survive, while those in wooded areas winter more successfully.

In spring - March till into June - the weevils leave their winter quarters and eat holes in the blossom buds ("squares"), feeding there and the females lay their eggs, one in a hole, but generally do not lay an egg in a square where one is already present. Later they attack the developing seed cases ("bolls") in the same way.

The eggs generally hatch in about 3 days and the larva, white, legless and with a brown head, eats out the inside of the square or boll, so the seeds, if they develop at all, will have only little cottony fibres, this taking a week to 12 days. It then changes to a pupa where it fed and remains in this stage 3 to 5 days before the adult beetle emerges.

Climatic conditions affect it, but the average length of time from egg to adult is 2 to 3 weeks. Thus there is time in a season for from 2 or 3 to 8 or 10 generations. Late in the fall when unattacked bolls have become scarce, the beetles will lay eggs in those already infested, but the squares are preferred to deposit in.

Infested squares open widely ("flare") and drop off or hang down, wilted. During August and September the weevils fly freely and this is the time when the spread of the insect has chiefly occurred. After frosts come they go into winter quarters.