Chromaphis juglandicola Kaltenbach
Systematic position: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Aphidoidea, Aphididae.
Common name: Walnut aphid, Small walnut aphid.
Geographical distribution: Of south-eastern Europian origin, it is now in the Middle East, North Africa, Central Europe, India, China and California. Distribution Maps of Plant Pests, Map 787, CABI 2014.
Host plants: Walnut (Juglans regia L.) and pecan (Carya illinoinensis L.).
Morphology: The young nymphs are yellow, the adults are yellow-green with a pair of dark spots on each abdominal segment, 1.3-2.5 mm in length. A yellow-white population has been reported from India and California.
Life history: This aphid lives and feeds on the underside of host leaves. It overwinters as eggs, which hatch in the spring and later, during summer, raises 8-11 large alate parthenogenic generations. In autumn, at leaf drop, the sexual forms occur, mate and deposit their hibernating eggs in the basal cracks of host-tree bark and buds. Dry and hot periods can seriously reduce the pest’s numbers.
Economic importance: Chromaphis juglandicola is a destructive pest that attacks walnut in many countries. Damage is due to sucking out tree nutrients and to excreting much honeydew, which is colonized by sootymold. Large populations (>15 aphids/walnut leaflet) that remain for 14 days, or more, may reduce the current season’s nut yield and its quality, along with reductions in the following season’s crop.
Sampling: A suggested method is choosing 10 trees at random and on each second week picking 12 leaflet/tree, until leaf drop. The number of aphids, mummies and predators are then recorded. Eggs can be sampled per 20 twigs/30 trees.
Chemical control: This approach is usually considered to be ineffective.
Biological control: The parasitoids Trioxys pallidus and Diaeretiella rapae are major enemies of the pest. The former was introduced from Iran into California and provided good control. Predatory Coccinellidae along with Syrphidae are at times key factors that regulate the pest’s numbers.
Cecilio, A. and Ilharco, F. 1997. The control of walnut aphid, Chromaphis juglandicola (Homoptera: Aphidoidea) in walnut orchards in Portugal. Acta Horticulturae 442: 399-406.
Nowierski, R .M. and Gutierrez, A.P. 1986. Numerical and binomial sampling plans for the walnut aphid, Chromaphis juglandicola (Homoptera: Aphididae). Journal of Economic Entomology 79: 868-872.
Ozkan, A. and Turkyilmaz, N. 1987. Determination of population fluctuations of the walnut aphid (Chromaphis juglandicola Kalt.) (Homoptera: Callaphididae) damaging pecan trees and of its natural enemies in Antalya Province in: Turkiye I. Entomoloji Kongresi Bildirileri, pp. 99-107.
Rakhshani, E., Talebi, A.A. and Sadeghi, S.E. 2000. Some biological characteristics of walnut aphid, Chromaphis juglandicola (Kaltenbach). Journal of the Entomological Society of Iran 20: 25-41.
Rakhshani, E., Talebi, A.A., Sadeghi, S.E., Kavallieratos, N.G. and Rashed, A. 2004. Seasonal parasitism and hyperparasitism of walnut aphid, Chromaphis juglandicola (Hom.: Aphididae) in Tehran Province. Journal of Entomological Society of Iran 23: 131-139.
Wani, S.A. and Ahmad, S.T. 2015. Biology and population dynamics of new colour morph of Chromaphis juglandicola Kalt.(Hemiptera: Aphididae) in Kashmir, India. Journal of Entomology and Zoology Studies 3: 28-31.