Peregrinus maidis Ashmead Homoptera Delphacidae

Natural History

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.

  1. The eggs are most often found along the midrib of leaves, especially on the basal and on the lowest portions of leaves on the plant. The eggs are inserted into a slit cut by the female, and 2-4 (usually two) eggs per oviposition site. The female deposits a drop of glue-like material after oviposition, sealing in the eggs. However, egg deposition also occurs below-ground on corn plants measuring less than about 30 cm in height. On such young plants, females oviposit in roots and in the below-ground portion of the stem. Access to these locations occurs through ant burrows and cracks in the soil. The eggs are reported to measure 0.75-1.1 mm long and 0.18-0.28 mm wide. They are curved in shape, tapering slightly at both ends, and resemble a banana in form. The eggs initially are transparent white, but as they approach hatch the dark embryo is visible. Duration of the eggs stage is normally 7-10 days. The mean oviposition rate is 19.6 eggs per day, with a lifetime fecundity of about 605 eggs.
  2. There normally are five instars, but the number may range from 4-6 depending on temperature and perhaps nutrition. The general body color is whitish, becomes yellowish by the third instar, but slightly darker dorsally during the latter instars. The eyes of the nymphs are reddish. The wing pads are first apparent during the fourth instar, extending back to about the middle of the first abdominal segment. In the fifth instar the wing pads extend to the third abdominal segment. The nymphs were reported to measure about 0.9, 1.3, 2.0, 2.8, and 3.2 mm long, respectively, in instars 1-5 by Quaintance (1898a). However, Tsai and Wilson (1986) indicated larger lengths, 1.4, 1.6, 2.3, 2.9, and 3.9 mm for instars 1-5, respectively. Keys to the nymphal instars were also provided by Tsai and Wilson (1986). Mean instar-spe-cific development times for insects cultured on corn at 27°C is 3.8, 3.0, 3.1, 3.1, and 4.2 days, respectively, for instars 1-5. Total nymphal development time when fed on corn was reported to require 65, 27, and 18 days at 15.6°, 21.1°, and 26.7°C. Although development time was rapid when nymphs were fed on corn; survivorship was higher when nymphs were provided with sorghum and barnyardgrass. Curiously, adult longevity was short when fed on barnyardgrass (Tsai, 1996). Young nymphs frequent leaf sheaths and other sheltered locations, presumably in response to the higher moisture levels found there. Older nymphs move freely about the plant. Both nymphs and adults leap freely when disturbed, but also they tend to move about the plant to avoid the source of disturbance. Nymphs are highly gregarious in habit, and often are found in association with adults.
  3. The adults occur in short-winged (brachy-pterous) and long-winged (macropterous) forms. Both
Peregrinus Maidis Maiz
Adult corn delphacid.

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.

Damage

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).

Management

  1. Fields are normally invaded by winged forms of corn delphacid, with highest insect densities found along the margins of fields. New corn fields are most commonly invaded by insects from older corn fields, so densities are highest at the juncture of new and old crops. When higher densities occur, the insects are more likely to be found in the center of fields. Therefore, field margins should be the principal focus of sampling programs (Takara and Nishida, 1983).
  2. Insecticides are used to prevent invading insects from establishing and reproducing in corn fields. Contact and systemic foliar insecticides, and systemic insecticides applied to the soil, are effective (Nishida, 1978; Tsai et al., 1990).

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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Responses

  • amaranth gaukrogers
    Why midribs of leaves get reddish due to oviposition by Delphacids?
    2 years ago
  • Marmadoc
    How to draw a peregrinus maidis?
    7 months ago

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