Chaitophorus nigrae

Identification & Distribution

Adult 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. Chaitophorus pallipes, where abdominal tergites VII & VIII are distinctly paler). There seems to be seasonal variation; in early summer specimens, the colourless areas are the largest. The hairs on antennal segment III are mostly pointed, with the longest being about 3 times the basal diameter of that segment. The fused apical rostral segment (RIV+V) is 0.125-0.150 mm long and is 0.9-1.3 times as long as the second hind tarsal segment (HTII). The mesonotum and abdominal tergites I-VI have a distinct pattern of reticulate imbrication, at least on pleural areas, although the degree of reticulation is variable. The dorsal abdominal hairs are mostly long and pointed. The legs, especially the tibiae, are unexpectedly pale although the femora of mid and hind legs are usually light brown or grey (cf. Chaitophorus stevensis, which has those femora very dark). The first tarsal joints have 5 hairs, rarely on one or two legs 6 hairs (cf. Chaitophorus viminalis, which usually has 6-7 hairs on the first tarsal segments - rarely 5). The siphunculi are dusky, without any clear surrounding area on the dorsum, but the rims of the siphunculi are usually pale (cf. Chaitophorus pallipes, which has the siphunculi unpigmented, with a clear surrounding area). The cauda is very little knobbed in dorsal view; sometimes there is a slight neck, but in some samples the apical portion is almost parallel-sided. The body length of adult Chaitophorus nigrae apterae is 1.7-2.5 mm. Immatures may be black, brown, orange, or even dark green (see pictures below).

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.

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 & Ecology

Colour

Chaitophorus 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 attendance

Chaitophorus 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 host

Chaitophorus nigrae has been recorded on 6 species of Salix (Salix cordata, Salix elegans, Salix exigua, Salix fluviatilis, Salix irrorata, Salix nigra).

• Blackman & Eastop list 8 species of aphid as feeding on black willow (Salix nigra) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 3 as occurring in Britain (Show British list).

• Blackman & Eastop list 5 species of aphid as feeding on sandbar willow (Salix exigua) worldwide, and provide formal identification keys (N.B. we have added Chaitophorus nigrae on the basis of Ebbers & Barrows, 1980) (Show World list). Of those aphid species, Baker (2015) lists none as occurring in Britain.

Damage and control

We have found no references to Chaitophorus nigrae causing any damage to willow trees, although honeydew may prove a nuisance.

Acknowledgements We are especially grateful to Claude Pilon for pictures of Chaitophorus nigrae (for more of her excellent pictures see, and, and). We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

References Ebbers, B.C. & Barrows, E.M. (1980). Individual ants specialize on particular aphid herds (Hymenoptera: Formicidae; Homoptera: Aphididae) Proceedings of the Entomological Society, Washington 82(3), 405-407. Full text Hille Ris Lambers, D. (1960). The genus Chaitophorus Koch in North America (Homoptera, Aphididae). Tijdschrift voor Entomologie 103, 1-30. Full text Richards, W.R. (1972). The Chaitophorinae of Canada (Homoptera: Aphididae). The Memoirs of the Entomological Society of Canada 104 Supplement S87, 1-109. Abstract Williams, A.H. et al. (2004). Feeding records of aphids (Hemiptera: Aphididae) from Wisconsin. The Great Lakes Entomologist 37 (1&2), 71-75. Full text