spirea.jpgSpirea Aphid, Aphis spiraecola Patch and
Apple Aphid, Aphis pomi DeGeer

I. Introduction: The apple aphid (AA) is widely distributed throughout North America. This is a species imported from Europe in the early 1800's. Recently, close inspection of presumed AA colonies has revealed that a substantial proportion of these colonies is a different species, the spirea aphid (SA), a native aphid species. Since the two species are difficult to distinguish without the use of high magnification and since we are currently managing these two species similarly, both species will be discussed together as green aphids (GA).

II. Hosts: The AA feeds primarily on apple and pear, but will also attack both hawthorn and quince. The SA is known to feed on apple and spirea. It is the main aphid pest of citrus worldwide, having made a shift to several tropical crops in the 1950's. It feeds on a variety of vegetable crops as well. Due to the apparent shift in species composition from the AA to the SA, this aphid now probably uses the same hosts as the AA. For years it has been assumed that SA used spirea as its primary host, on which overwintering eggs are placed, and shifted to other hosts in the late spring. In 1983, it was shown to use citrus as a primary host for the first time, in Japan. It has recently been shown in Virginia that SA uses apple as a primary host, as well.

III. Description: The eggs of both species are small, shiny and black. They cannot be differentiated from the two other species of aphids inhabiting the tree at the same time, rosy apple aphid (RAA) and apple grain aphid (AGA). It is difficult to distinguish young stem mothers of these species; they have not yet developed their characteristic color patterns. The cornicles of the young nymphs are smaller than those of the RAA but larger than those of the AGA especially when the nymphs are very young, when the cornicles of AGA are barely swollen protuberances. RAA also has longer antennae than the others; antennae of AGA are the shortest. The young GA nymphs which develop into stem mothers in the spring are wingless females and are bright green in color, although not as dark as the AGA. As the colonies develop throughout the summer, the aphids can vary considerably in color from a yellow-green to a light green, with black cornicles (Plate 37). The alate adults (with wings) of SA and AA can be distinguished by the following characteristic: for the AA, the veins in the forewing are distinctly pigmented, especially the cubitus and media (the two veins crossing from the thick front vein across the central part of the wing). Other characters to separate the two species, while usable for wingless viviparae, are impossible to use in the field. Oviparae (egg-laying females, produced in the fall) of SA have greatly swollen tibiae on the hind legs. The oviparae of both species have six antennal segments (unlike AGA); the front of the head is gently rounded, lacking the central tubercle of RAA. Males (also occurring in the fall) of SA are winged, unlike those of AA.

IV. Biology: The eggs are laid mostly on the bark or on the buds in the fall by wingless females after they mate with the males. Warm periods during the winter, as well as cold rains near hatch, cause some natural mortality of eggs. Hatch occurs in the spring between the silver tip and half-inch green stages, especially around green-tip. The young nymphs develop into stem mothers which are wingless, pear-shaped females, bright green in color. Stem mothers require 12-20 days to reach maturity. Adults often appear around bloom. These give birth to a generation of green viviparous (producing live young) aphids, ranging from 40-80 young per female. About three-quarters of this generation develop into winged females; the rest remain wingless. The winged forms spread colonies to other parts of the tree or other trees and orchards. About one-half of the second generation and some of the later generations may develop wings and disperse. Wingless aphids produce more offspring than alates. Unlike the RAA and the AGA, GA can live on the apple tree all year around. Both species breed continuously during the summer. There are seven to 17 generations, depending on whether first or last young of each generation are considered. In August and during the autumn months, they are found almost exclusively on water sprouts or terminals of young trees that are still growing, and it is at such locations that the male and female sexual forms are produced, at about the fourteenth generation. Males mate throughout their activity period, but many oviparae fail to become fertilized because of the relative scarcity of males (males are less numerous than oviparae and do not live as long). Oviparae may deposit eggs from early October until early December.

Spirea aphid is more tolerant of certain insecticides (esfenvalerate, methomyl and imidacloprid) than apple aphid.  On the other hand, spirea aphid is somewhat more susceptible than apple aphid to azinphosmethyl.

V. Injury: Recent research at VPI&SU has shown that SA and AA have generally similar effects on photosynthesis and tree growth. Both nymphs and adults suck sap from apple trees. They prefer to feed on the succulent, young tissue found at the ends of terminal shoots and water sprouts. They can curl the foliage if high populations develop and stunt tree growth, especially on young trees. Indirect injury results when aphids secrete large amounts of honeydew on which grows a black fungus that smuts both the fruit and leaves and causes considerable discoloration, especially of early apples. Honeydew is often prevented from accumulating by rains.

VI. Monitoring: During the dormant period, examine twigs for overwintering eggs, to aid in selecting timing of delayed dormant sprays.

Neither SA and AA is usually an early season problem (i.e., before bloom), therefore, monitoring usually begins in late May and June when populations generally begin to increase. At this time select the major cultivar in the block and sample 10 actively growing shoots (not water sprouts) on each of five trees. On each shoot, determine the number of leaves that have wingless aphids. Calculate the average number of leaves per shoot infested with aphids across all trees. Aphid populations should be scouted for and managed until the terminal shoots harden off. This will occur later in the season for young trees than mature trees.

If an average of >4 leaves per shoot are infested with one or more wingless aphids, an application of an insecticide is warranted. There are a number of natural enemies of aphids which have proven effective for biological control of aphid in mid-Atlantic apple orchards. They include a number of syrphid and cecidomyiid fly larvae, chrysopid larvae, and coccinellid adults and larvae (see section on natural enemies of aphids). If greater than 20% of GA colonies have predators, there is a good chance of biological control. Growers should recognize and monitor these species before deciding on management practices.

This is taken primarily from a chapter by D.G. Pfeiffer, L.A. Hull, D.J. Biddinger, & J.C. Killian on apple indirect pests, reprinted with permission from Mid-Atlantic Orchard Monitoring Guide, published by NRAES, 152 Riley-Robb Hall, Ithaca, New York 14853-5701.
Additional reading:
Back to Virginia Apple Page
Back to Home Page for "Arthropod Management in Fruit Crops" course
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