Distribution. Although now found throughout the world in tropical areas, this species is likely a native to Africa. In the United States it is reported to occur as far north as Washington D.C. and Ohio, and south to Florida and Texas. As a pest, however, it is best known from subtropical areas such as southern Florida and Texas. It also is common in Hawaii and the Caribbean, including Puerto Rico.
It has been suggested that corn delphacid was introduced to Mesoamerica in pre-Columbian times, and was responsible for crop destruction and collapse of the Mayan civilization. However, post-Columbian introduction of this species also has been suggested (Nault, 1983).
Host Plants. Among cultivated crops, corn delph-acid feeds principally on corn and sorghum. Sugarcane is sometimes suggested as a host, but there is no evidence that it is a good host plant. Forage grasses such as pangolagrass, napiergrass, and vaseygrass are poor hosts (Namba and Higa, 1971), but nymphs are able to complete their development on some weed grasses such as barnyardgrass, Echinochloa crusgalli; itchgrass, Rottboellia exaltata; and goosegrass, Eleusine indica (Tsai, 1996).
Natural Enemies. Several natural enemies have been imported into Hawaii, where corn delphacid was especially damaging. Some attack principally sugarcane leafhopper, Perkinsiella saccharicida Kirkaldy, and only slightly affect corn delphacid. Egg parasites, Anagrus spp. (Hymenoptera: Mymaridae) were established in Hawaii for suppression of corn delphacid, but their effectiveness is uncertain. A predator, Cyrtor-hinus lividipennis Reuter (Hemiptera: Miridae), is reported to be an important suppressive agent in Hawaii (Liquido and Nishida, 1985).
This delphacid is attended by ant species, though the attending ants differ in the various regions of the world. The ants collect honeydew produced by the delphacids, sometimes building shelters for the del-phacids, and fending off wasp parasitoids (Dejean et al, 1996).
Life Cycle and Description. Several overlapping generations occur during the summer or growing period. A complete generation requires about 30 days.
males and females occur in each form. The short-winged forms measure about 3 mm long, whereas the body of the long-winged forms measure about 2-2.6 mm. The body color is greenish or brownish-yellow. The front wings (when present) are greenish or brownish, darker distally. The abdomen is smoky, with lateral yellow stripes. The legs are pale or brownish. Duration of the adult stage is about 30 days for both males and females at 21-27°C.
The general biology and appearance were described by Quaintance (1898a) and Verma (1955), but Tsai (1996) and Tsai and Wilson (1996) gave more detailed descriptions of morphology and development.
Corn delphacid affects corn both directly and indirectly. Direct injury includes removal of plant sap, tissue damage resulting from oviposition, and production of honeydew which supports the growth of sooty mold. Excessive growth of sooty mold impedes photosynthesis. The principal damage by these insects, however, results from the transmission of plant disease. Corn delphacid is the vector of two important diseases of corn—maize mosaic virus and maize stripe virus. Both nymphs and adults are capable of virus transmission, which results in yellowing and stunting of the corn. For maize strip virus, nymphs acquire the virus after feeding for about four hours and can transmit the disease after 4-5 days, and for the period of their life. They also can transmit the virus transovarially (Tsai and Zitter, 1982). For this insect to transmit maize mosaic, 10 days is required, and the insect also remains capable of disease transmission (Carter, 1941).
Cultural Practices. The strong association of corn delphacid with corn suggests that crop rotation will limit damage, especially if new crops are relocated at a considerable distance from previous crops. However, some grass weeds also support corn delphacid. If these grasses cannot be eliminated, they should be monitored for delphacid populations and sprayed, if necessary, to prevent the insects from infesting the crop.
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