Scyphophorus acupunctatus, the sisal weevil or agave weevil, is a species of polyphaga beetle of the family of the Curculionidae. Sisal weevil larvae, known as picudo del agave or "nixtamal worms", are a traditional food in parts of Mexico.
Adults bore into leaves of young plants or plants with weak fibres, and if perforated sisal hearts are infected by fungi, the central shoot becomes red and soft, producing conditions suitable for development of the larvae, which die quickly in the absence of moisture. Plants over 2 years old are not generally perforated, and only leaves too small to cut are damaged. Suckers that have been too deeply planted may begin to rot at the base and weevils are then attracted to them as secondary pests. Weevil attack on healthy leaves too strong to penetrate produces a mottled area of dead epidermis approximately 20 cm from the leaf base; this damage is only distinguishable from that caused by friction because it occurs before the leaf has unfolded (Harris, 1934).The most obvious symptoms are leaf holes 1 cm in diameter, and where these are observed on mature leaves, six or seven leaves on the same plant are usually also affected. The younger the leaf, the nearer the hole is to the tip. These are the result of the weevil boring into hearts of the plants under 2 years old when the young leaves are still unfolded.
When plants are healthy, injury does not develop further, but when growth is not sufficiently vigorous around the perforations, entrance of rot-causing organisms can occur. These infect the central shoot, which becomes red and soft, and the plant dies. Large suckers used for planting are more liable to serious injury than bulbils, which are damaged by the weevil penetrating between the bases of the outer leaves into the bulb, or small suckers with newly cut bases, which also attract feeding. Deep planting and injury to the leaf bases are, however, the primary causes of the death of the plants in many cases, the weevil acting only as a secondary pest. Large, healthy sisal plants are sometimes attacked by the adults when the leaves are still part of the heart or central shoot. When cut, the leaves are found to have areas of brown, dried-out epidermis approximately 20 cm from the base. This causes discoloration of the fibres, but the actual damage to them is not considerable. This type of injury is exceptional in that it appears to depend on the population density of the weevils and not on the health of the plants (Harris, 1936).In Tanzania, S. acupunctatus was originally recorded as ovipositing in the hearts of sisal plants, in which the resulting larvae fed so that the leaves, when unfolded, appeared as if riddled by bullets. In 1931, a new form of injury was observed in the Pangani district. Innumerable fine holes, as if made with a needle, occurred in the outer heart leaves on the outer surface of the leaf-edge approximately 5 cm from the base. The injury often becomes noticeable only after 1-2 years, when the large percentage of discolored fibres attracts attention (Schwencke, 1934).
