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Brown ambrosia aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Adult apterae of Uroleucon ambrosiae are red-brown to dark brown or dull red (see two pictures below), with black siphunculi and a pale cauda. The antennae are dusky to black, but paler on antennal segments I, II and the base of segment III. There are 14-27 secondary rhinaria on segment III, and a terminal process which is 5.5-6.5 times the base of antennal segment VI (cf. Uroleucon leonardi, which has a terminal process 6.3-7.2 times the base of segment VI). The rostrum fully reaches the third pair of coxae, with the apical rostral segment (RIV+V) longer than the base of antennal segment VI. There are dusky scleroites on the dorsum of the abdomen. Abdominal marginal tubercles are absent (cf. Macrosiphum nigrotuberculatum, which has small black marginal abdominal tubercles). The hind tibia usually has a pale or dusky basal section, but this is not as pale as the cauda for more than 0.5 of its length (cf. Uroleucon ivae on Ambrosia & Iva, which has the tibia as pale as the cauda for more than 0.7 of its length). The second hind tarsal segment (HTII) is short at only 0.75-0.9 times the length of RIV+V (cf. Uroleucon pseudoambrosiae, which has HTII longer at 0.9-1.1 times RIV+V). The siphunculi are 1.1-1.3 times the caudal length, have a third of their length with polygonal reticulation, and are uniformly dark (cf. Uroleucon rudbeckiae, whose siphunculi are much paler at the base). The pale cauda tapers to a rather acute point, and bears 7-8 hairs on each side. The Uroleucon ambrosiae aptera body length is 2.5-3.5 mm.
Images above, copyright Jesse Rorabaugh, no rights reserved.
The Uroleucon ambrosiae alate vivipara is coloured similarly to the aptera, apart from having dark brown thoracic lobes and a dark blotch on tergite VI posterior to the base of each siphunculus. The antennae are entirely black, with 31-45 secondary rhinaria on antennal segment III. The rostrum hardly reaches the third pair of coxae. The dusky abdominal scleroites are often reduced or lacking.
The images below show clarified mounts of an apterous and an alate vivipara of Uroleucon ambrosiae.
In eastern and northern USA, and Canada, Uroleucon ambrosiae is mainly found on Ambrosia and Iva. Moran 1985 felt that records from other plants were probably misidentifications of other species. However, populations in south-western USA, and Central and South America are far less specific, having been found feeding on the leaves and flower-stems of many additional genera in the Asteraceae including Achillea, Aster, Cichorium, Eupatorium, Lactuca, Rudbeckia and Senecio. The more polyphagous form is sometimes regarded in South America as a subspecies, Uroleucon ambrosiae ssp. lizerianum. The species is monoecious holocyclic in temperate North America with alate males, but it is usually anholocyclic in southern USA, and Central and South America.
Other aphids on the same host
Uroleucon ambrosiae has been recorded on 8 ragweed species (Ambrosia ambrosioides, Ambrosia artemisiifolia, Ambrosia confertiflora, Ambrosia deltoidea, Ambrosia paniculata, Ambrosia polystachia, Ambrosia psilostachya, Ambrosia trifida).
Uroleucon ambrosiae has been recorded on 3 sumpweed species (Iva cheiranthifolia, Iva oraria, Iva xanthifolia).
Uroleucon ambrosiae has been recorded on 1 Rudbeckia species (Rudbeckia hirta).