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Mouse-ear hawkweed aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution:
In life Uroleucon pilosellae apterae are dark reddish grey-brown with black siphunculi and a yellow cauda (see first two pictures below). The antennae are about as long as the body. The fused apical segments of the rostrum (RIV+V) are about 1.2 times the length of the second tarsal segment (HTII). Well developed antesiphuncular sclerites are present. The tibiae have a paler middle section and the coxae are dark (see micrographs below). The first tarsal segment has only 3 hairs (see micrograph below) (cf. Uroleucon cichorii and Uroleucon obscurum which both have 5 hairs on the first tarsal segment). The siphunculi are 1.6 to 1.9 times the length of the cauda (cf. Uroleucon obscurum which has the siphunculi 1.0-1.4 times the length of the cauda). The number of caudal hairs is 12 to 18. The body length of an adult aptera of Uroleucon pilosellae is 2.2-2.5 mm.
The micrographs below show dorsal and ventral views of an apterous Uroleucon pilosellae, and a close-up of the first and second tarsal segments showing the number of hairs.
The clarified slide mounts below are of adult viviparous female Uroleucon pilosellae : wingless, and winged.
Uroleucon pilosellae is found on the flower stems of Hieracium pilosella and possibly other Hieracium throughout Europe. Laamari et al. (2013) have recently recorded it on Leontodon hispidus.
Biology & Ecology
Whether Uroleucon pilosellae is both specific to Hieracium pilosella and is the only Uroleucon regularly feeding on this plant is unclear. Heie (1980-1995) states explicitly that the otherwise very similar Uroleucon cichorii does not occur on this plant, whilst Blackman & Eastop (2006) record 5 Uroleucon species on it, including Uroleucon cichorii.
The leaves of mouse-ear hawkweed (Hieracium pilosellae) are setose above and on the margins, and white beneath with long soft hairs (see below first).
The flower bracts and stem are clothed with dense stellate, glandular and pilose hairs (see above second). These characteristics are markedly different from other Hieracium species, so it would not be unreasonable to expect that a different species has evolved to exploit Hieracium pilosellae.
Other aphids on same host:
Uroleucon pilosellae has been recorded on Pilosella officinarum, Pilosella caespitosa, Hieracium aurantiacum, Hieracium bauhini, Hieracium cymosum, and Hieracium echioides.