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Dark-tipped evening primrose aphidOn this page: Identification & Distribution Biology & Ecology Population dynamics Ant attendance Other aphids on the same host
Identification & Distribution
Adult apterae of Aphis oestlundi are a more or less uniform pale green. The siphunculi are mainly pale, but with darker tips (cf. Aphis grossulariae, Aphis epilobiaria, Aphis oenotherae, which all have completely pale siphunculi, and cf. Aphis fabae, Aphis gossypii, Aphis spiraecola, all of which have dark or dusky siphunculi). The antennal terminal process is only 1.2-1.9 times the length of the base of antennal segment VI (cf Aphis praeterita, which has the terminal process 3.3-4.7 times the base of that segment). The apical rostral segment (RIV+V) is quite short at 1.35-1.70 times the length of the second hind tarsal segment (HTII) (cf. Aphis nasturtii, which has RIV+V less than 1.40 times the length of HTII). The anterior half of the subgenital plate has 4-6 hairs. The cauda and the anal plate are pale to slightly dusky. The body length of adult Aphis oestlundi apterae is 1.8-2.0 mm.
Both images above by permission, copyright Claude Pilon, all rights reserved.
The alate Aphis oestlundi (see second picture above and below) has black head and thorax, a light green abdomen with dusky lateral areas, a spot at the base of each siphunculus posteriorly - and sometimes traces of median dashes on the abdomen. The antennae and siphunculi are dusky. The legs are pale, except for the tips of the tibiae and tarsi which are black, and the cauda is pale. There are well developed marginal tubercles on the prothorax and on abdominal tergites I and VII. The cauda is somewhat elongated and constricted near the base, and bears 2-3 hairs on each side.
First image above by permission, copyright Claude Pilon, all rights reserved.
Aphis oestlundi lives on the leaves and stems of evening primrose (Oenothera biennis). It does not host alternate. Sexuales develop in autumn on the undersides of leaves of the host plant located near the ground. The males are apterous, have a brown head, a yellowish green thorax with the pleural, lateral and anterior areas of dorsum brownish, and a yellowish green abdomen with the brown siphunculi. The ovipara is a deep bright green, with the head, antennae, siphunculi, anal plate, apices of tibiae, and tarsi, brownish. Aphis oestlundi is restricted to North America, where it is found widely.
Biology & Ecology
In Minnesota Wyckhuys et al. (2009) monitored the temporal patterns in abundance of several aphid species on their respective summer hosts, including Aphis oestlundi. The proportion of plants infested by Aphis oestlundi was quite low (usually less than 0.25) with maxima reached in two locations in June/July and in another in August/September.
In Minnesota Wyckhuys et al. (2009) found that Aphis oestlundi was tended by 5 species of ants: Formica obscuripes, Lasius alienus, Lasius neoniger, Myrmica cf. americana and Myrmica n. sp.. For Aphis oestlundi, the degree of ant tending ranged from 26.1% in north central Minnesota to 75.0% in south central Minnesota.
Other aphids on the same host
Blackman & Eastop list 15 species of aphid as feeding on evening primrose (Oenothera biennis) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 10 as occurring in Britain (Show British list).