|Crop Knowledge Master|
Rhopalosiphum maidis (Fitch)
|Corn Leaf Aphid|
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educational Specialist
Department of Entomology
The primary host of this aphid is corn (maize). Alternative hosts include: barley, green beans, manila hemp, millets, papaya, potato, rice, squash and other Gramineae, sorghums, sugarcane, tobacco and wheat.
The corn leaf aphid is cosmopolitan in distribution throughout the tropics, subtropics and warmer temperate regions. It has also been reported in Japan and southern Scandinavia. Introduced to Hawaii by commercial trade, this aphid was first reported on Oahu in 1906 and has since spread to all major islands.
This aphid infests all parts of the corn plant above ground. The most severe damage occurs to the tassel, often aphid populations become so dense within the protective sheath of the tassel that proper pollination does not occur and incomplete ears result. Leaves may become encrusted with aphids and wilt. Under sever conditions leaves will be dry and chlorotic.
Corn leaf aphid excretes copious amounts of honeydew. This honeydew may attract attending ants, serve as media on which sooty mold may grow, and provides food for corn earworm moths and other pests of corn.
This aphid is a vector of many virus diseases affecting cereals and other crops. Persistent viruses include barley yellow dwarf, maize leaf fleck, and millet red leaf. Non-persistent viruses include abaca mosaic, maize dwarf mosaic and sugar cane mosaic. In Hawaii it has been found to be a vector of cucumber mosaic virus (South celery mosaic strain), onion-yellow-dwarf virus and papaya ringspot virus.
Populations are primarily composed of females that reproduce without mating. They do not lay eggs but instead birth live young. Males do not occur in Hawaii. They occur only in cooler climates. Males are occasionally found and sexual reproduction may occur.
The developmental rate, number of progeny, and adult longevity is greatly influences by temperature, host plant species and host plant age. 86û F is the optimum temperature for population increase on barley (El-Ibrashy et al., 1972). At this temperature the birth rate is greatest on immature barley plants and lowest on senescent plants. Nymphs produced per female was 37 on young plants, 41 on older immature plants, 34 on mature plants and 18 on senescent plants. El-Ibrashy et al. (1972) provides detailed life table information.
Generations are continuous in Hawaii. There are possibly as many as 50 generations per year.
Most aphids in temperate regions overwinter in the egg stage. Since this species is a tropical species overwintering eggs have not been observed.
There are four nymphal stages. The upper and lower development thresholds are 95û F and 50û F, respectively. Developmental rate is inversly related to temperature. Nymphal development is completed in about 16 days at 58û F, 9 days at 68û F, 7 days at 77_ F, and 5 days at 86û F (El-Ibrashy et al., 1972).
First instar nymphs are light green. The tips of head, antennae and legs are slightly darker than the body. Second instar nymphs are pale green. The head, abdomen and antennae are darker than the body and the legs are paler. The eyes are red. A constriction on the third antennal segment is distinct. At the third stage the constricted third antennal segment is divided into two segments. The body is still pale green, but slightly darker on the sides. Legs are darker than the body. The head is a dark green color.
Adults are winged (alate) or unwinged (apterous), elongate and measure between 1/25 to 1/12 inch in length. They are yellow-green to dark olive green or bluish green and often have a light powdery covering. Their color tends to be are darker during cool weather and could be a pale green during warm weather. Head, antennae and legs are black.
On barley, adults live for 11 days at 86û F and 17 days at 59û F. Females birth 2 -4 nymphs per day for 9 to 12 days and live an additional 2 - 5 days (El-Ibrashy et al, 1972). In another study conducted at 77.9û F females had a 6 day, birthed nymphs for 16 days, and lived for an additional 10 days (Foott, 1977).
There are differences in the numbers of nymphs produced and lifespan of winged and wingless females. At 77û F wingless females produced an average of 68 nymphs (range = 57 - 77). Winged aphids produced an average of 49 nymphs (Adams and Drew, 1964).
Winged individuals are produced in response to changes in weather, population density, and host plant quality. In sugarcane fields alates are produced when the grass goes to seed (Swezey, 1928). Wet weather and high population densities have also been reported to increase the production of alate aphids.
The corn leaf aphid is most active in temperatures ranging from 62.6 and 80.6û F.
Populations in Hawaii are controlled by an immigrant wasp, Aphelinus maidis, that parasitizes aphid nymphs. This wasp is a common aphid parasite that also attacks several other species of aphids. 3 other wasps belonging to the Aphelitae genus also attack the corn leaf aphid in Hawaii: A. semiflavis (Howard), A. gossypii (Timberlake) and A. mali (Haldeman). Important predators include maggots of the syrphid flies, Allograpta sp. and several species of lady beetles.
This pest is easily controlled by contact or systemic insecticides.
Adams, J. B. and M. E. Drew. 1964. Grain Aphids in Brunswick. II. Comparative Development in the Greenhouse of Three Aphid Species on Four Kinds of Grasses. Can. J. Zool. 42: 741-744.
Belvett, V. B., R. Y. Sun and A. G. Robinson. 1965. Observations on Laboratory Rearing of Grain Aphids (Homoptera: Aphididae). Can. J. Zool. 43: 619-622.
Blackman, R. L. and V. F. Eastop. 1984. Rhopalosiphum maidis (Fitch). pp. 340-341. Aphids on the World's Crops: An Identification and Information Guide. John Wiley and Sons: Chichester, New York, Brisbane, Toronto, Singapore, 466 pages.
Carter, J. J. 1957. On the Biology of the Corn Leaf Aphid. J. Econ. Ent. 50: 110-112.
El-Ibrashy, M. T., S. El-Ziady and A. A. Riad. 1972. Laboratory Studies on the Biology on the Corn Leaf Aphid, Rhopalosiphum maidis (Homoptera: Aphididae). Entomol. Exp. Appl. 15(2): 166-174.
Foott, W. H. 1977. Biology of the Cornleaf Aphid, Rhopalosiphum maidis (Homoptera: Aphididae), in Southwestern Ontario. Canadian Entomol. 109(8): 1129-1135.
Hassan, M. S. 1957. Studies on the Morphology and Biology of Aphis maidis Fitch., in Egypt. Bull. Soc. Entom. Egypte. 41: 199-211.
Hill, D. S. 1983. Rhopalosiphum maidis (Fitch). pp. 204. In Agricultural Insect Pests of the Tropics and Their Control, 2nd Edition. Cambridge University Press. 746 pages.
Muddathir, K. 1976. Studies on the Biology of Wheat Aphids in the Gezira (D. R. Sudan). Beitr. Ent., Berlin. 26(2): 465-470.