Acyrthosiphon pisum

BY ZACK THOMAS

Common Name : 'Pea Aphid', 'Green Pea Aphid'

Family: Aphididae
Superfamily: Aphidoidea
Order: Homoptera
Class: Insecta

[ photo courtesy of UC statewide IPM project]

Page Contents

Identification

Geography

Natural History

How to Encounter

References

€ Identification €

A. pisum are rather large (2.5-4.4 mm), pale green or pink aphids usually in colonies on young growth or pods of Leguminosae; only tree recorded from is Robinia pseudoacacia. 2n=8 (Blackman &;Eastop, 1994). Immatures are very lightly dusted with wax. Apterae 2.5-4.4 mm, alatae 2.3-4.3 mm (Blackman &;Eastop, 1984). The instar of A. pisum are indistinguishable from those of A. kondoi and a few other closely related species. However, there are several distiguishing characteristics of A. pisum matures:

"4-5mm long, green, with a shiny appearance; antennae are pale green or brown, but always have a dark band at the joint of segments 3 and 4 (approximately one-quater length from the head). The other joints in the antenna are usually banded. Ther is normally a dark band at the middle joint of each leg, which is otherwise pale brown or green, and the tips of the siphunculi are usually dark. As in bluegreen aphids, A. kondoi , winged pea aphid adults are similar to the wingless form apart from having two pairs of wings. They differ from winged bluegreen aphids in having the area surrounding the wing bases pale green." (Hill, 1979)

€ Geography€

Acyrthosiphon pisum
AREA	STATUS	REFERENCES
North America: Continental United States; Canada	Yes	Blackman &;Eastop, 1984
Eastern North America: United States east of Mississippi; Ontario and eastern Canada	Yes	Blackman &;Eastop, 1984
Southeastern United States: AL AR DE DC FL GA KY MD NC SC TN VA WV	Yes	Blackman &;Eastop, 1984
Southern Appalachian States: AL GA KY MD NC SC TN VA WV	Yes	Blackman &;Eastop, 1984
Ridge and Valley	Yes	UGA Natural History Museum Distribution Map
Coastal Plain	Widespread	UGA Natural History Museum Distribution Map
Piedmont	Widespread	UGA Natural History Museum Distribution Map
Georgia	Yes	UGA Natural History Museum Distribution Map
Clarke County, Georgia	Yes	Zack Thomas, Pers. Ob. Also: UGA Museum of Natural History Distribution Map
Sams Farm	Common	Zack Thomas, Pers. Ob.
Old Field	Very Common	Zack Thomas, Pers. Ob.
Wetland	?	-
Woods	None Observed	Zack Thomas, Pers. Ob.
1-Hectare Plot	None Observed	Zack Thomas, Pers. Ob.

€ Natural History €

Pea aphids consume the nutritive fluid transported in the phloem of their host plant. This is done directly by inserting a proboscis into the phloem tissue. The internal pressure within the phloem is generally enough to pump the 'food' into the pea aphid's gut (Dixon, 1973). In comparison to many other aphid species that are entirely host specific, the pea aphid is found on a few different families of plants which are the alfalfas, clovers, and field beans. From an economic standpoint, the pea aphid is considered a minor pest on alfalfas and clovers and, as the name suggests, a major threat to infested field pea crops (Hill, 1987).
The life cycle of the pea aphid begins in February/March, depending on the local clinmate, when overwintering eggs hatch on a host plant. All hatching eggs are female which then reproduce parethenogenetically, with each individual producing 4-12 females per day. All young are born live. Populations increase and in mid-May winged females (with a minor contingent of winged males) are produced which then emigrate in search of new host plants. The population continues to expand from June through September, or as long as the host plant continues to produce adequate quantities of sap and there are no hard freezes. By October, oviparous females are produced along with a few males (although males are rarely recorded) which then breed and lay eggs for overwintering (Hill, 1987).
Due to their high rate of reproduction, pea aphid populations can increase explosively in favorable conditions. As their host plants are all agriculturally important, such outbreaks of population can have serious economic consequences. For this reason there has been much energy expended in researching means of controlling pea aphid populations. Pesticides were a primary means of control for many years but overuse in some areas has lead to the evolution of resistant strains (Minks &;Harrewijn, 1987). Therefore, in the last two decades, the focus of research has shifted to the study of biological controls, including the use of fungi the naturally parasitize the pea aphid (Gutierrez and Pickering, 1991) and employing parasitoid wasps (Mertins, 1985).

€ How to Encounter €

As the pea aphid is a common agricultural pest in the southeastern United States. As such it is easily found from spring through early fall in most any field that was formerly used for agriculture and which has not become reforested. A. pisum can be found in particular at a location known as Sam's Farm in Athens, Georgia. This former farm is located at mile maker 16 on highway 78 south of Athens. There is an open field on the site. Examination of any of numerous plant species, but especially red clover, will reveal a preponderance of A. pisum.

€ References €
Blackman, R.L. and V.F. Eastop. 1984. Aphids on the World's Crops: An Identification Guide. John Wiley &;Sons. New York, NY. 210-214.

Blackman, R.L. and V.F. Eastop. 1994. Aphids on the World's Trees: An Identification and Information. University Press, Cambridge. England.

Dixon, A.F.G. 1973. Biology of Aphids. Edward Arnold (Publishers), Ltd. London. 55 pages. (ISBN: 0-7131-2421-0)

Gutierrez, A.P. and J. Pickering. 1991. Differential Impact of the Pathogen Pandora neoaphidis Humber on the Species Compostition of Acrythosiphon aphids in Alfalfa. The Canadian Entomologist 123: 315 320.

Hill, Dennis S. 1987. Agricultural Insect Pests of Temperate Regions and Their Control. Cambridge University Press, England. 624 pages. (ISBN: 0-521-24013-1)

Hill, R.L. 1979. Bluegreen lucerne aphid, Acyrthosiphon kondoi Shinji, and pea aphid, A. pisum, life cycles. DSIR Information Series No. 105/28. (ISSN: 0077-9636)

Mertins, J.W. 1985. Hyperparasitoids from Pea Aphid Mummies, Acyrthosiphon pisum, in North America. Annals of the Entomological Society of America 78: 186-197.