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Aphis gregalisWestern rabbitbrush aphidOn this page: Identification & Distribution Other aphids on the same hostIdentification & DistributionAdult apterae of Aphis gregalis (see two pictures below) are bluish-green to yellowish-green, with darker head and pronotum, and variably-developed dorsal abdominal dark markings. During spring and early summer these markings may vary from a few patches in front of the siphunculi to broad bands on all abdominal and thoracic segments; in late summer and fall the dark markings may be almost or completely absent. The body is covered with a thin dusting of grey wax. The head is rounded in front, with only slight antennal tubercles. The antennae are black, apart from the base of antennal segment III. They are about 0.4 times body length, with circular secondary rhinaria distributed 0-3 toward the distal end of the segment III, and 0-1 on IV. The terminal process is 1.1-1.5 times the base of antennal segment VI (cf. Aphis ornata, which has the terminal process 1.3-2.0 times the base of antennal segment VI - note the overlap of ranges and see note below). The rostrum reaches the third coxae, and the apical rostral segment is not extended as a needle-like tip (cf. Aphis chrysothamni, which has the apical rostral segment extended as a needle-like tip). Marginal tubercles are well developed on most abdominal segments, as well as on the first two thoracic segments. Siphunculi are black, and slightly bent downward. The cauda is black, almost conical, with a very slight constriction near the base. The anal plate is black and rounded. Body length of adult Aphis gregalis apterae is 1.2 to 1.85 mm.
Images above copyright Jared Shorma under a creative common licence. Note: It is unclear whether the western USA species, Aphis gregalis, differs from the very similar eastern USA species, Aphis ornata. Blackman notes there are no clear distinguishing characters in slide-mounted specimens, the only difference being their colour when alive - bluish green to yellowish green in Aphis gregalis, or pale pinkish in Aphis ornata. However, it seems that some 'Aphis gregalis' colonies on rabbitbrush in western USA have both pink and green forms of both immatures and adult apterae (see picture below from Oregon). This suggests the two species may be synonomized in the near future.
Image above copyright Andrew Jensen under a creative common licence. The alate vivipara of Aphis gregalis (not pictured) has the head and thorax black, and abdomen bluish-green to dusky, with slight waxy covering. The antennae are dusky, with secondary rhinaria distributed 2-7 on segment III, and 1-2 on segment IV. The rostrum reaches the third pair of coxae. Siphunculi are short, black, and slightly bent. The body length of the alate is 1.4 to 1.7 mm. Aphis gregalis is monoecious on rabbitbrush (Chrysothamnus and Ericameria spp.), often in large colonies on shoot tips, leaves and flower-stems, causing stunting and distortion of growth. This distortion affords partial protection and concealment for the colonies. Greenish-red to reddish-brown oviparae and apterous reddish-brown males have been found in October. The species is found on the western slopes of the Rocky Mountains, USA. Other aphids on the same hostAphis gregalis has been found on 1 Ericameria species (Ericameria nauseosa).
Aphis gregalis has been found on 2 Chrysothamnus species (Chrysothamnus parryi, Chrysothamnus viscidiflorus).
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