Distribution. This species is a native to the western hemisphere, but not to the United States. It apparently was introduced into Louisiana about 1855, and has since spread to the other Gulf Coast states. It inhabits only the warmer parts of these states, however. Sugarcane borer also occurs throughout the Caribbean, Central America, and the warmer parts of South America south to northern Argentina.
Host Plants. Sugarcane borer attacks plants in the family Gramineae. Though principally a pest of sugarcane, this insect also feed on other crops such as corn, rice, sorghum, and sudangrass. Many wild or weed grasses are suitable hosts, including Johnsongrass, Sorghum halepense; Paspalum sp.; Panicum spp.; Holcus sp.; and Adropogon sp.
Natural Enemies. The importance of natural enemies in corn-cropping systems is not known, because most studies involve only sugarcane. Ants are reported to be important predators of sugarcane borer in sugarcane fields, capable of reducing damage by over 90% (Bessin and Reagan, 1993). Although much of the attention has been focused on red imported fire ant, Solenopsis invicta Buren, other species such as Phei-dole dentata Mayr and P. floridana Emery (all Hymenop-tera: Formicidae) also are important (Adams et al., 1981).
Effective parasitoids are not established in the United States. Egg parasitoids, Trichogramma sp. (Hyme-noptera: Trichogrammatidae), are possibly the most important naturally occurring parasitic insects. Although they are not very abundant early in the season, by autumn they may inflict almost complete destruction of borer eggs. The most important imported parasitoid is Agathis stigmaterus (Cresson) (Hymenoptera: Braconidae), which was reported by King et al. (1981) to affect, on average, less than 12% of borers. Lixophaga diatraeae (Diptera: Tachinidae) has the potential to cause high levels of parasitism, but does not persist well (see biological control, below). A wasp introduced from India, Cotesia flavipes Cameron (Hymenoptera: Braconidae), is an important late-season parasitoid late in the summer within Florida. Other parasitoids include Orgilus elasmopalpi Muesebeck, Apanteles diatraeae Musebeck, Apanteles impunctatus Musebeck (all Hymenoptera: Braconidae), Euplectrus plathypenae Howard, and Syntomosphyrum clisiocampe (Ashmead) (both Hymenoptera: Eulo-phidae).
The comparative assessment of natural enemies in sugarcane and sorghum conducted by Fuller and Reagan (1988) probably offers some insight into the role of natural enemies in corn, because cultural practices in sorghum and corn are similar. Predator densities were higher in sugarcane owing to the greater abundance of red imported fire ant. However, Orius spp. pirate bugs (Hemiptera: Anthocoridae), lacewings (Neuroptera: Chrysopidae), tiger beetles (Coleoptera: Cicindelidae), spiders, and foliage-dwelling ground beetle larvae (Coleoptera: Carabidae) were more abundant in sorghum fields. Suppression of predators with soil-applied insecticide affected predation in both agroeco-systems, with borer populations 40-60% higher where predator abundance was reduced.
Weather. An inverse relationship between rainfall and borer abundance has been reported from both Louisiana and Puerto Rico. Heavy rainfall, and particularly winter rainfall resulting in flooding, depresses borer survival (Holloway et al., 1928). This is thought to result from prolonged emersion of stalks containing overwintering larvae in flood water. Also, young larvae living in the whorl of corn or sugarcane are quite tolerant of short-term emersion, but heavy rainfall while they are dispersing could lead to death because they are washed from the plants. In addition to rainfall, cold winter temperature is reported to depress larval survival rates in Louisiana.
Life Cycle and Description. Overwintering occurs in the larval stage, with pupation in the spring. In Louisiana and Texas, adults become active by April or May, and the borer population continues to cycle until autumn. Development time is highly variable, so the generations overlap considerably, obscuring population trends. There is potential for 4-5 generations to occur annually, but moths are abundant only in spring and autumn (Fuchs and Harding, 1979), so perhaps there are fewer generations. During the summer a complete generation may require only 25 days, whereas during the winter over 200 days are needed.
Sugarcane borer larva, summer form.
confused with southern cornstalk borer, and definitive separation involves microscopic examination of the mouthparts. Sugarcane borer, however, is much less likely than southern cornstalk borer, Diatraea crambi-doides (Grote), to be found infesting corn. (See color figure 81.)
The biology of sugarcane borer was described by Holloway et al. (1928) and a bibliography was authored by Roe (1981). Several wheat germ-based diets are suitable for rearing (Roe et al., 1982). A key to the Diatraea larvae can be found in Peterson (1948), and Stehr (1987), and to the adults in Dyar and Heinrich (1927). A key to stalk borers associated with corn in southern states was presented by Dekle (1976); this publication also includes pictures of the adults. A key to common stalk boring caterpillars also is included in Appendix A.
Although generally regarded as a potentially serious pest of sugarcane, other crops are rarely at risk.
Sugarcane borer is a minor pest of sweet corn even in Florida, where the weather favors its survival and sugarcane is found abundant (Kelsheimer et al., 1950). Damage by sugarcane borer to grain corn was described by Flynn and Reagan (1984) and Flynn et al. (1984). Larvae injure corn in two ways. Early in the season they attack the whorl, feeding on the young developing tissue. If such damage is light, the result may be only series of holes across the leaf blade. If such damage is extensive however, the growing point of the plant may be killed and plant growth stunted. This condition is called "dead heart.'' Later in the season the larvae descend to the stalk and burrow into it. Large larvae tunnel through the stalk, causing the plant to be prone to breakage. On occasion, especially during the second generation, larvae may burrow into corn ears (Rodriguez-del-Bosque et al., 1990).
Cultural Practices. Sugarcane is the principal host of sugarcane borer, and proximity of corn to sugarcane is an important determinant of borer abundance in corn. Moths deposit more eggs on sugarcane than corn when these hosts are in close proximity, and avoid pubescent cultivars (Sosa, 1990). It is advisable to destroy cane trash in the winter as it reduces overwintering by larvae, but the practice of burning does not always kill borers deep within the stalks. Borers overwinter within corn stalks, but usually only late-planted corn is suitable. Some sugarcane cultivars display considerable resistance to sugarcane borer (Bessin et al., 1990; Bessin and Reagan, 1993), which presumably can reduce overall abundance of borers and infestation potential in corn. Grain corn varieties with resistance to sugarcane borers also have been identified (Maredia and Mihm, 1991).
Biological Control. The Caribbean region and tropical areas of South America have been surveyed extensively for natural enemies. Many species were introduced into the United States, but few could be established (Clausen, 1978). Agathis stigmatera (Cresson) (Hymenoptera: Braconidae) was successfully imported from Argentina and Peru, and though it is well-established in both Florida and Louisiana, its effect on sugarcane borer is minimal. The fly, Lixophaga diatraeae (Townsend) (Diptera: Tachinidae) was imported and released repeatedly, but tends to disappear or dissipate after a few years. In some countries, augmentative releases are used to attain high levels of parasitism in sugarcane borer, and this has been attempted in Louisiana (King et al., 1981). Some authors have claimed success with augmentative releases of Trichogramma spp. (Hymenoptera: Tricho-grammatidae), but this has proven difficult to implement in the United States (Long and Hensley, 1972).
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