Eggs within a cluster all hatch about the same time and larvae tend to congregate in the whorls, feeding almost immediately. Larvae feed through the leaf tissue and tunnel through the midrib. After molting once or twice, larvae burrow into the stalk.
There are two forms of larvae for summer and for winter. Summer larvae are whitish with brown heads and bear large brown spots on each body segment. Winter larval form lack spots. Larvae pupate in tunnels within the plant. The pupal stage usually last eight to nine days before adults moths emerge, but under cool conditions moths may not emerge for 22 days.
The adults are yellowish brown moths with a wingspan varying from 3/4 inch to one inch for males and one inch to 1 1/2 inches for females. The forewings have numerous narrow brown lines extending their length. The hind wings of females are white and hind wings of males are darker. Sugarcane borer moths are nocturnal, hiding during daylight hours. At dusk, female moths begin to deposit eggs continuing through the evening. Moths may deposit eggs for up to four days. Sugarcane borer adult live three to eight days.
Sugar cane borer can be a serious pest of sugar cane when larvae bore into the stalks. The tops of mature plants tend to weaken or die, sometimes breaking off. Larvae feeding in the whorl of a young plant can kill the inner leaves, resulting in a condition known as "dead heart." When borers are present, the amount and purity of juice extract is reduced with sucrose yield reductions of 10 to 20 percent. Seed cane can be attacked and the tunneling makes the seed piece susceptible to fungal infection.
Sugar cane borer is principally a pest of sugarcane, but feeds on other crops such as corn, sorghum, and Sudan grass and many wild or weed grasses.
Sugar cane borer has several natural enemies. Eggs are parasitized by Trichogramma sp., tiny stingless wasps. The Trichogramma sp. population increases during the summer. A wasp introduced from India, Cotesia flavipes Cameron, attacks sugar cane borer larvae. Larvae also are preyed upon by pirate bugs Orius spp., lacewings larvae, ground beetle larvae and spiders.
A sample of five stalks taken from five plants spaced 3 millimeters apart gives a good indication of borer larval density. At higher densities sugar cane borer populations are more aggregated and levels are more difficult to estimate. When sugar cane borer population densities are high, foliar insecticides applications to sugar cane can provide significant yield increases even in the presence of predation and resistant varieties. Insecticides must be applied when larvae are small, before they burrow into the stalk. Only low levels of control are possible later when larvae leave their tunnel during the process of pushing out excrement.
All cane trash should be destroyed in the winter to reduce overwintering by larvae. Burning fields does not always kill borers deep within the stalks. Some sugar cane cultivars are available that have considerable resistance to sugar cane borer.
>> Eric T. Natwick is an entomologist at the University of California-Imperial County Cooperative Extension.
>>The Cooperative Extension serves all residents of the Imperial Valley.