Aulacorthum solani Kaltenbach Homoptera Aphididae

Natural History

Distribution. Foxglove aphid occurs throughout the United States and southern Canada. As a pest, its effect is greatest in the eastern regions of the continent. Foxglove aphid is found almost world-wide, but is probably of European origin.

Host Plants. Although having a very wide host range, foxglove aphid is a pest principally of potato. In the northernmost potato-growing areas in eastern North America it is sometimes the dominant aphid species on this crop, but in other areas it is displaced by green peach aphid, Myzus persicae (Sulzer); potato aphid, Macrosiphum euphorbiae (Thomas); and buckthorn aphid, Aphis nasturtii Kaltenbach. Foxglove aphid also occurs on a few other vegetables including celery, chervil, lettuce, pea, and tomato, and also on alsike, red, and white clover. In Asia, but not North America, it frequently colonizes soybean. Fruit crops that on occasion support foxglove aphid include apple, raspberry, and strawberry. It may be found on such flowers as calla lily, cineraria, Easter lily, foxglove, gladiolus, pansy, salvia, tulip, and violet. Among the numerous weeds known to support foxglove aphid are bittersweet, Solanum dulcamara; buttercup, Ranunuculus spp.; cinquefoil, Potentilla spp.; common chickweed, Stellaria media; common plantain, Plantago major; dock, Rumex spp.; fall dandelion, Leontodon autumnalis; orange hawkweed, Hieracium aurantiacum; king devil, Hieracium floribundum; oxeye daisy, Chrysanthemum leucanthemum; pigweed, Amaranthus spp.; purslane, Portulaca oleracea; shepherdspurse, Capsella bursa-pastoris; and smartweed, Polygonum spp. The overwintering hosts of foxglove aphid in cold-winter climates are foxglove, which is the basis of its common name, and hawkweed species, which apparently are more important hosts. In Europe, additional overwintering hosts are known, but in North America, woody plant hosts are not required for overwintering by either the egg or adult stages.

Natural Enemies. The natural enemies of foxglove aphid are not well documented in North

America. Among the predators of foxglove aphid are the common lady beetles (Coleoptera: Coccinellidae), some lacewings (Neuroptera: Chrysopidae), flower flies (Diptera: Syrphidae), and the predatory midge Aphidoletes aphidimyza (Rondani). In Maine, several parasitoid species have been collected, including Aphi-dius nigripes Ashmead, Praon spp., Monoctonus sp., and Aphidius spp. (all Hymenoptera: Aphidiidae), and Aphelinus semiflavus Howard (Hymenoptera: Eulophi-dae) (Shands et al., 1965). In Europe, parasitoids reportedly exert good control of foxglove aphid (Robert and Rabasse, 1977), and this is likely the case in North America also. In addition, fungi affect these aphids.

Life Cycle and Description. Foxglove aphid can remain on its primary hosts, foxglove and hawkweed species, throughout the year. Alternatively, it can disperse during the summer to crops and weeds. In either case, the population peaks in August or September. In cold-winter climates such as Maine, overwintering occurs in the egg stage. In climates with warmer winters, such as New Jersey, aphids may overwinter as adults.

  1. The eggs are normally shiny, black, and elliptical in form. They measure about 0.6 mm long and 0.3 mm wide. They are found principally on foxglove and hawkweed. They are deposited by oviparous adults in October and November, and hatch in March.
  2. There are five instars. Mean nymphal development time is 2.4, 1.8, 2.4, 2.7, and 3.2 days for instars 1-5, respectively, at 21°C. After the 12-13 day developmental period, apterous adults commence parthenogenetic reproduction almost immediately.
  3. The general body form of the adults is best described as pear-shaped, with the posterior portion greatly expanded relative to the anterior portion. The tubercles at the base of the antennae are pronounced but straight-sided, facing neither inward as in green peach aphid, nor outward, as in potato aphid. The apterous females measure 1.5-3.0 mm long. They are principally yellow, yellowish-green, or green, with the head and thorax also pale. In some specimens the dorsal surface is darker. The abdominal cornicles are moderately long, thin, and tapered, measuring 0.4-0.7 mm long; they vary in color from almost colorless to dark, and with dark tips. The reproductive period lasts about 15-30 days, with females producing an average of 60 offspring per female (range 25-81). Adults perish a few days after completing reproduction. The alate females are similar in size, measuring 2.0-2.9 mm long. The abdomen is pale green, olive green, or green, but the head and thorax vary from dusky-yellow to almost black with a brown tinge. The alatae usually bear dark bars or patches dorsally on the abdomen, and there are dark patches at the base of the cornicles. As in the apterous form, the cornicles are long and thin, measuring 0.5-0.7 mm long and varying in color. The veins of the wings are dark.

A brief treatment of foxglove aphid biology was found in Patch (1928). A morphological description was presented by Cottier (1953), and phenology and host plant relations by Wave et al. (1965). Developmental biology was given by MacGillivray and Anderson (1958). Foxglove aphid was included in the keys of Palmer (1952) and Blackman and Eastop (1984).

Damage

Aphid populations cause potato leaves to curl, especially if the leaves are young when attacked. Foxglove aphid apparently produces toxic saliva, as it causes plant deformity and stunting at lower densities than other potato-infesting aphids. This aphid also transmits numerous plant viruses.

Management

Management of foxglove aphid has not been well-studied, probably because this aphid is usually only

Foxglove Aphid
Adult female foxglove aphid, wingless form.

Adult female foxglove aphid, winged form.

one component of the aphid complex, and often a minor component. The sampling and management techniques discussed in the sections on green peach aphid, potato aphid, and buckthorn aphid are likely applicable to foxglove aphid.

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