Therioaphis trifolii (Monell)
(Also known as Therioaphis maculata)
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Aphidoidea, Aphididae.
Common name: Spotted alfalfa aphid.
Geographical distribution: The Mediterranean Basin, Central Asia and North America. CIE Map #126, 1991 (revised).
Host plants: Alfalfa (Medicago) and clover (Trifolium).
Morphology: The body of apterous and alate females is lemon-green and is covered by rows of tubercles (hence “spotted”). The darker siphunculi are very short and the cauda is truncated. Body length is 1.3-2.1 mm.
Life history: In the Middle East the aphid reproduces by viviparous parthenogenesis the year around, alate forms appearing when colonies become overcrowded. A generation may be completed in one week at 26ºC, the threshold of development is around 8ºC, and about 40 generation can annually be raised in the Middle East. The populations of the pest consist of two biotypes, one more suited to alfalfa (the spotted alfalfa aphid), the other more to clover (the spotted clover aphid).
Economic importance: Usually this aphid is a minor pest of alfalfa and clover in the Middle East, but it may occasionally damage these crops. Heavily infested plants turn yellow (chlorotic) and an injected toxin, as well as a transmitted plant virus, aggravate the damage. In addition, plants become contaminated by the honeydew and the subsequent sootymold.
Management
Plant resistance: Several commercial varieties of alfalfa are resistant to the pest.
Chemical control: The spotted alfalfa aphid has developed resistance to most organophosphates, but pyrethroids may still control it.
Biological control: The pest is attacked by predators, including Coccinellidae, Syrphidae and Chrysopidae, by endoparasitoids, such as the Aphidiidae, and by entomopathogenetic fungi. Three Aphidiidae (an Aphelinus sp., Praon exsoletum (Nees) and Trioxys complanatus Quilis] from Israel were successfully introduced into California to control the pest there. An indigenous strain of the fungus Zoophthora radican (Brefeld) was obtained in Israel and successfully introduced into Australia.
References
Holtkamp, R.H., Edge V.E., Dominiak, B.C. and Walters, P.J. 1992. Insecticide resistance in Therioaphis trifolii f. maculata (Hemiptera: Aphididae) in Australia. Journal of Economic Entomology 85: 1576-1582.
Milner, R.J., Soper, R.S. and Lutton, G.G. 1982. Field release of an Israeli strain of the fungus Zoophthora radicans (Brefeld) Batko for biological control of Therioaphis trifolii (Monell) f. maculata. Journal of the Australian Entomological Society 21: 113-118.
Milne, W.M. 1998. Comparative performance of two biotypes of Therioaphis trifolii (Monell) (Hemiptera: Aphididae) on clovers (Trifolium) and medics (Medicago). Australian Journal of Entomology 37: 350-355.
Ruggle, P. and Gutierrez, A.P. 1995. Use of life tables to asses host-plant resistance in alfalfa to Therioaphis trifolii F. maculata (Homoptera, Aphididae) - hypothesis for maintenance of resistance. Environmental Entomology 24: 313-325.
Swirski, E. and Amitai, S. 1999. Annotated list of aphids (Aphidoidea) in Israel. Israel Journal of Entomology 33: 1-120.
Website