Insect identification > Coleoptera > Rhynchophora > Sweet-potato weevil

Sweet-potato weevil

The sweet-potato weevil (Cylas formicarius Fab.). - A tropical insect first reported in the United States about 1875 and now present in Florida, Georgia, Alabama, Mississippi, Louisiana and Texas, attacking the sweet potato.

The adult, unlike the other snout beetles here considered, is very slender, about a quarter of an inch long, with a black head, reddish prothorax and legs and dark blue elytra. The prothorax is strongly narrowed, forming a noticeable "waist" for the insect.

The eggs of this pest are laid singly in small holes eaten in the stem or any exposed potato. They hatch in a few days and the grubs in the stems burrow through them down to the potato, then tunnel irregularly about, becoming full­grown in 2 or 3 weeks. The grub now forms a cavity and in this it pupates for about a week and then a few days later eats its way out and may leave the potato or may remain there and lay eggs for another generation in the same potato in which it itself developed, and this process may continue until the entire potato is destroyed.

As long as food is available, one generation after another is thus produced, but when no more can be found the adult insects live along for a considerable time without feeding, attacking the plants and laying their eggs in them whenever more appear. Adult beetles feed on the leaves and stems somewhat.

As soon as tunnels in the potato are formed, the tissues around them change color and decay soon follows, so that an attack quickly ruins the value of the crop.