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Hairy-tailed aphidsOn this page: Mollitrichosiphum nigrum
Mollitrichosiphum apterae are quite large, and usually elongate with long siphunculi. The median portion of the frons is flat, and antennal tubercles are only slightly developed. The antennae are 6-segmented. In alatae, there are numerous secondary rhinaria on antennal segment III. The media vein of the fore wing is twice branched, and the hind wing has two oblique veins. First tarsal chaetotaxy (=bristle arrangement) is 7-7-7 (fore-mid-hind). In the aptera the hind tibia has numerous transverse ridges, possibly stridulatory in purpose. The underside of the abdomen is spinulose (=spinule-covered) and forms two distinct elongated areas of dense spinulosity postero-laterally. The siphunculi are cylindrical, elongated, and densely covered with spinules. The cauda and anal plate are rounded or transversely oval.
There are eighteen species of genus Mollitrichosiphum worldwide, with eleven in China. The species of this genus colonize young leaves and branches of plants belonging to several families, mostly Fagaceae or Betulaceae (Alnus), but also including Elaeagnaceae, Fagaceae, Juglandaceae, Lauraceae, Meliaceae (Meliosma), Proteaceae, Sabiaceae, and Sapindaceae. Until now, sexual morphs have been recorded for three species, but most of the species seem to have at least some anholocyclic populations.
Mollitrichosiphum nigrum (Black hairy-tailed aphid) China, Japan?
Adult apterae of Mollitrichosiphum nigrum are elongate pear-shaped with the body less than 2.2 times longer than maximum abdominal width (cf. Mollitrichosiphum tenuicorpus, which is more than 2.2 times longer than the maximum width of the abdomen). In life the head, thorax, abdomen and siphunculi are shining black, sometimes with a thin dusting of white wax (see picture of specimens with identity unconfirmed below) (cf. Mollitrichosiphum yamabiwae, which is yellow-brown in life). Their antennae are pale except for segments I & II and the apices of segments III-VI, which are dark. The terminal process is about 1.4 times as long as the base of antennal segment VI. The ultimate rostral segment is long and wedge-shaped. The dorsal hairs of the abdomen are thick and long, and mostly pointed (cf. Mollitrichosiphum taiwanum, whose dorsal hairs are mostly bifurcate). The legs are mostly pale brown with dark tarsi. The hind tibiae have 49-63 transverse ridges in the basal 0.75 of their length (cf. Mollitrichosiphum yamabiwae, which has less than 40 ridges on the hind tibia). The siphunculi are extremely long, 0.6-0.7 times the body length, slightly swollen in the middle with a distinct flange, and with densely spinulose imbrications. Each siphunculus bears 110-130 long hairs. The cauda is semi-round, with 8-10 hairs. The anal plate is transversely elliptical, with 16-22 hairs. Immature Mollitrichosiphum nigrum (see lower part of picture below) are greenish-orange with spinal, pleural and marginal lines of scleroites.
Images above by permission, copyright Akihide Koguchi, all rights reserved.
The alate Mollitrichosiphum nigrum (not pictured) has antennal segment III with 14-16 round secondary rhinaria. There are 49-53 short transverse ridges in the basal 0.6 of the hind tibia. The veins of the wings and the pterostigma are dark brown. There are large sclerotized dark patches on tergites III-VI. The siphunculi are extremely long, 0.8-1.1 times body length, with 189-210 long and short hairs.
Mollitrichosiphum nigrum has mainly been found on Meliosma species (Sabiaceae), where they feed on the leaf undersides. They have also been collected from Ailanthus altissima and Elaeagnus pungens (Zhang & Qiao, 2010). Until now Mollitrichosiphum nigrum has only been found in China, whilst the specimens shown here were found in Japan. Hence the uncertainty about the identity of the aphids pictured here as Mollitrichosiphum nigrum. However Mollitrichosiphum is the only genus of aphid that has been found on Meliosma species, and the only species recorded on Meliosma are Mollitrichosiphum nigrum, Mollitrichosiphum yamabiwae, Mollitrichosiphum tenuicorpus and Mollitrichosiphum taiwanum. Of these, only Mollitrichosiphum nigrum is described as black in life; the others are yellow, yellow-brown or pale brown (see Blackman in Aphids on Worlds Plants).