Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Capitophorus have pale or almost translucent slender aphids with elongate legs and antennae. Wingless viviparae have long capitate hairs at least on the head and posterior abdominal segments. Winged viviparae only have short hairs and have a dark dorsal abdominal patch.
Wingless viviparae of Capitophorus carduinus are pale greenish white to yellowish green, almost translucent, often with two indistinct darker green longitudinal stripes. The terminal process of the antenna is 4.6-6.3 times the length of the base of the last antennal segment. Capitophorus carduinus have long capitate hairs on the head and posterior abdominal segments (clearly visible in the micrographs below). Their siphunculi are pale, slender and cylindrical, and are 2.4-3.5 times the length of the cauda. The siphunculi have no distal reticulation and are without dark apices (cf. Capitophorus elaeagni which has siphunculi with dusky to dark apices). The body length of wingless viviparae is 1.6-2.2 mm.
The alate Capitophorus carduinus (see second picture above) have a pale greenish abdomen with a blackish green dorsal patch. Unlike for the aptera, the siphunculi are dark. The ovipara is greenish to yellowish with rather dark swollen hind tibiae. The male is alate and has a greyish green abdomen with three crossbars.
Unlike many of the other Capitophorus aphids whose primary host is oleaster (hence sometimes known as oleaster aphids) the green thistle aphid does not host alternate. Capitophorus carduinus lives on the undersides of the lower leaves of thistles (Carduus and Cirsium species). The green thistle aphid is found in Europe and in various Asian countries.
Apterae in spring populations of Capitophorus elaeagni on the primary host are pale green. Their abdominal dorsum is reticulate or sculptured, and abdominal tergites 1-4 each have 6-8 hairs, usually one pair each of spinal, pleural and marginal hairs. The siphunculi are cylindrical or tapering and are dusky to dark at the apices. The body length of wingless viviparae on the primary host is 1.9-2.5 mm. Winged viviparae produced on the primary host have a black head and thorax, black antennae and a blackish dorsal abdominal patch. Wingless viviparae on the secondary host (various Compositae) are greenish white to yellowish green with dark tips to the siphunculi. The body length of wingless viviparae on the secondary host is 1.4-2.5 mm.
Note: our identification of these aphids as Capitophorus elaeagni was not checked microscopically. Blackman (2010) indicates that the sexual phase of Capitophorus elaeagni that occurs on Elaeagnus in continental Europe has not yet been recorded in Britain, casting doubt on our identification. It could instead be Capitophorus similis which host-alternates between Elaeagnus and Tussilago or Petasites. That said, we observed these forms in the south coast which, if sexual forms of Capitophorus elaeagni occur in Britain, is the most likely place to find them.
The common oleaster aphid host alternates from oleaster (Elaeagnus) or sea buckthorn (Hippophae) to various thistles and daises (Asteraceae). Capitophorus elaeagni is found over most of the temperate and warm temperate parts of the world.
Apterae of Capitophorus hippophaes on the primary host (sea buckthorn) in spring are pale green or sometimes reddish, with a faint pattern of green spots. On the secondary host (redshank) the aphids are pale greenish to yellowish white (see first picture below), occasionally with longitudinal rows of green spots. The antennae are 0.8-1.2 times the length of the body. The siphunculi of Capitophorus hippophaes are 2.0-2.4 times the length of the cauda, with the distal two thirds to one half slightly swollen. (cf. Capitophorus elaeagni & Capitophorus similis both feeding on sea buckthorn which do not have swollen siphunculi) . The cauda has a cylindrical basal part and a triangular, pointed distal part. The body length of adult apterae is 1.7-2.4 mm.
Capitophorus hippophaes alates are greyish-green with a black head and thorax, dark antennae, legs and siphunculi and a large quadrate dark green patch on the dorsal abdomen. Fundatrices are broadly oval, greenish with reddish spots, and their antennae are dark, 5-segmented and have a short processus terminalis.
Capitophorus hippophaes host alternates: The primary hosts are various species of Hippophae (sea buckthorn) and Elaeagnus (oleaster). The secondary hosts are various Polygonum and Persicaria species. Aphids live on the undersides of the leaves. Capitophorus hippophaes occurs in Europe, north Africa, south-west Asia, and has been introduced into North America. A subspecies, Capitophorus hippophaes javanicus occurs on Polygonaceae in south-east Asia, Australia, New Zealand, South America, and also in California, USA.
On the primary host both the fundatrix and viviparous females of Capitophorus similis are pale greenish, frequently a little reddish, and with longitudinal rows of green spots. The siphunculi are thin, not swollen, and about 3.5 times the length of the cauda (they are a little shorter on the fundatrix) (cf. Capitophorus hippophaes which have the distal two thirds to one half of their siphunculi slightly swollen). On the secondary host, the apterous viviparous female Capitophorus similis is whitish to yellowish white (see first picture below). The antennal terminal process is 6.1-7.5 times the length of the base of that segment. The siphunculi are thin, cylindrical, slightly curved towards their inner sides, with the apices curved outwards, and 3.7-5.0 times as long as the tongue-shaped cauda.
The alate female Capitophorus similis (see second picture above) has a greenish-white abdomen, with rather large, dark marginal sclerite and postsiphuncular sclerites, a black quadrangular dorsal patch on tergites 3-6, and small sclerites on the posterior tergites.
The buckthorn-butterbur aphid host alternates between the primary host, buckthorn (Hippophae) and the secondary host, coltsfoot (Tussilago) or butterbur (Petasites). Males and winged females are produced in autumn. Capitophorus similis is distributed throughout Europe into the eastern Himalayas in Asia.