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Chaitophorus nigraePale-streaked willow aphidOn this page: Identification & Distribution Biology & Ecology Colour Ant attendance Other aphids on the same host Damage & ControlIdentification & DistributionAdult apterae of Chaitophorus nigrae are variably pigmented. At maximum pigmentation they are entirely shiny black (see first picture below). More often they are dark with a more or less marked pale median stripe from head to tergite VI (see second picture below). At a minimum they are pale with brownish pleural intersegmental sclerites, but abdominal tergites VII & VIII are always evenly dark-pigmented across the tergite (cf. Most of the information given above, plus further information on possible subspecies, is given by Hille Ris Lambers (1960). However, the subspecies are not accepted by Richards (1972) who describes additional morphological characteristics.
First and third images above by permission, copyright Claude Pilon, all rights reserved. Chaitophorus nigrae alatae (see third picture above) have dark dorsal abdominal cross-bands, which often coalesce between abdominal tergites II-VI. They have 9-17 secondary rhinaria irregularly placed on antennal segment III, with some also on segments IV and V. The terminal process is 2-3 times as long as base of the last antennal segment.
The pictures below show clarified mounts of Chaitophorus nigrae, aptera and alate.
Both images above copyright CBG Photography Group, Centre for Biodiversity Genomics under a Creative Commons Attribution Non-commercial Share-Alike license. Chaitophorus nigrae lives in sometimes large colonies on leaves and petioles of new growth of various willow (Salix) species, especially black willow (Salix nigra). They are usually attended by ants. Large, pale oviparae and alate males occur in September-November, and the species overwinters as eggs on willow. Chaitophorus nigrae is widely distributed in North America, extending from Alaska eastwards to New Brunswick and southwards to California and North Carolina. Biology & EcologyColourChaitophorus nigrae is a rather variable species, not least in their colour. The immatures seem to be a mostly a light pinkish-brown (see first picture below).
Image above by permission, copyright Claude Pilon, all rights reserved. Sometimes, however the young immatures are a bright orange.
Image above by permission, copyright Claude Pilon, all rights reserved. The aphid below is a fairly strongly marked adult Chaitophorus nigrae with a pale median area on the thorax and anterior abdominal segments, tergites VII-VIII evenly dark across the abdomen and dusky / dark siphunculi.
Image above by permission, copyright Claude Pilon, all rights reserved. But the specimen in the second picture at the top of the page is perhaps less straightforward, with it being difficult to assess if the siphunculi are 'dusky' or 'clear'. Ant attendanceChaitophorus nigrae is, like most Chaitophorus species, tended by ants. Williams et al. (2004) listed Chaitophorus nigrae as being attended by the ant Dolichoderus taschenbergi on the petioles & undersides of leaves of a Salix species. Ebbers & Barrows (1980) looked at how much individual ants specialise on particular aphid colonies when collecting aphid honeydew. Three ant-aphid associations were examined, one of which was Formica subnuda tending Chaitophorus nigrae on leaves of Salix exigua ssp. interior (other associations were Formica subnuda tending a Pterocomma species on branches of Salix exigua ssp. interior, and Camponotus noveboracensis tending a Chaitophorus species on petioles of Populus tremuloides.
Image above by permission, copyright Claude Pilon, all rights reserved. A total of 158 ants were marked individually in the three associations. Each association was then examined from one to four times a day for ten consecutive days. Of the marked ants 65% were seen again subsequently and, of these, 81% were seen at the same aphid colony. 10% changed colonies once, 6% twice, and 3% three times, with a mean colony constancy of 4 days. The authors concluded that specialization on particular colonies may be a way of maximizing their net energy gains from the aphids by avoiding wasting energy in searching for untended aphids or competing with other aphid-tending ants. Other aphids on the same hostChaitophorus nigrae has been recorded on 6 species of Salix (Salix cordata, Salix elegans, Salix exigua, Salix fluviatilis, Salix irrorata, Salix nigra).
Damage and controlWe have found no references to Chaitophorus nigrae causing any damage to willow trees, although honeydew may prove a nuisance.
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