Rhopalosiphum maidis (Fitch)
Taxonomic placing: Insecta, Holometabola, Hemiptera, Sternorrhyncha, Aphidoidea, Aphididae.
Common name: Corn leaf aphid.
Geographical distribution: Cosmopolitan; CIE Map # 67, 1971 (revised).
Host plants: Many Poaceae (Gramineae), occasionally on banana.
Morphology: The body of apterous females is bluish-green; the head, siphunculi and cauda are brown-black, body length is about 2.0 mm. The head, thorax, siphunculi, cauda and legs of alate females are black, the abdomen is blue-green. Body length is about 2.0 mm.
Life cycle: In the Middle East the corn leaf aphid reproduces throughout the year on wild grasses and commercial cereals by viviparous parthenogenesis. A cycle can be completed in one week and 35-40 generations may be raised annually, each female producing about 70 progeny. The optimum temperature for development is around 30°C, at which condition the life cycle is shortened and female survival increases. The threshold for development was calculated in the USA to be at 6.1°C. The nymphs that are born during the hot summer in the Middle East survive periods of high temperatures by aestivating within unfurled grass blades. Several biotypes of the pest that differ significantly in their rates of reproduction were recorded in the USA.
Economic importance: This leaf aphid is a major pest of corn (maize) in Egypt, heavy infestations reducing its yields by >35%. It is also an important pest of barley, millet, sorghum, sugar cane, wheat and sometimes banana in various parts of the world. Infested tissues wilt due to feeding and to the injection of toxins, resulting in yellow patches and longitudinal leaf curling. Tassels and silks may be covered with honeydew, which interferes with pollination, attracts ants and becomes contaminated by sootymold. The aphid is a vector of several virus diseases, including the debilitating maize dwarf mosaic virus (MDMV) and barley yellow dwarf luteovirus (BYDV).
Management
Monitoring: Yellow-pan water traps are in common use. Scouting of corn plots should be initiated when tassels emerge. Economic thresholds are variable in different regions and on various crops; treatment of corn should be considered if plants are under drought stress and if more than 50% of plants have >100 aphids/plant during tassel emergence.
Horticultural methods: In fields with a history of MDMV problem, grass weeds should be eliminated prior to planting corn.
Molecular methods: When R. maidis was offered transgenic Bt-corn (plants expressing the Cry1Ab protein of Bacillus thuringiensis) or artificial diets containing that protein, no residues of the toxin were found in their bodies.
Plant resistance: Varieties of barley, corn, sorghum and wheat that are resistant to the pest have been developed.
Chemical control: When insecticides become necessary, imidacloprid, applied as a seed treatment, reduces aphid numbers along with the virus diseases that it transmits.
Biological control: This pest is attacked by predatory Chrysopidae, Coccinellidae and Syrphidae and by the aphelinid endoparasitoid Aphelinus maidis (Timberlake), as well as by some Aphidiidae. Several species of Entomopathogenic fungi infect the aphid, but their effect on its populations is not known.
References
Al-Eryan, M.A.S. and El-Tabbakh, S.S. 2004. Forecasting yield of corn, Zea mays infested with corn leaf aphid, Rhopalosiphum maidis. Journal of Applied Entomology 128: 312–315.
Bayhan, E. 2009. Impact of certain corn cultivars on some ecological parameters of Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae). African Journal of Biotechnology 8: 785-788.
Capinera, J.L. 2008. Corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae). Encyclopedia of Entomology, pp 1070-1072.
El-Ibrashy, M.T., El-Ziady, S. and Riad, A.A. 1972. Laboratory studies on the biology on the corn leaf aphid, Rhopalosiphum maidis (Homoptera: Aphididae). Entomologia Experimentalis et Applicata 15: 166-174.
Gray, S.M., Bergstrom, G.C., Vaughan, R., Smith, D.M. and Kalb, D.W. 1996. Insecticidal control of cereal aphids and its impact on the epidemiology of the barley yellow dwarf luteoviruses. Crop Protection 15: 687-697.
Harvey, T.L., Seifers, D.L. and, Kofoid, K.D. 1996. Effect of sorghum hybrid and imidacloprid seed treatment on infestations by corn leaf aphid and greenbug (Homoptera: Aphididae) and the spread of sugarcane mosaic virus strain MDMV-B. Journal of Agricultural Entomology 13: 9-15.
Head, G., Brown, C.R., Groth, M.E. and Duan, J.J. 2001. Cry1Ab protein levels in phytophagous insects feeding on transgenic corn: implications for secondary exposure risk assessment. Entomologia Experimentalis et Applicata 99: 37–45.
Mescheloff, E. and Rosen, D. 1990. Biosystematic studies on the Aphidiidae of Israel (Hymenoptera: Ichneumonoidea). 4. The genera Pauesia, Diaeretus, Aphidius and Diaeretiella. Israel Journal of Entomology 24: 51-91.
Razmjou, J. and Golizadeh, A. 2010. Performance of corn leaf aphid, Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae) on selected maize hybrids under laboratory conditions. Applied Entomology and Zoology 45: 267–274.
Singh, S.R. and Painter, R.N. 1964. Effect of temperature and host plants on progeny production of four biotypes of corn leaf aphid, Rhopalosiphum maidis. Journal of Economic Entomology 57: 348-350.
Swirski, E. and Amitai, S. 1999. Annotated list of aphids (Aphidoidea) in Israel. Israel Journal of Entomology 33: 1-120.