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Bristly anthemid aphidsOn this page: Pleotrichophorus chrysanthemi glandulosus
Pleotrichophorus are medium-sized pale spindle-shaped aphids. They have fairly low antennal tubercles and a moderately developed median frontal tubercle. The antennae have a very long terminal process, and both apterae and alatae have secondary rhinaria on some of the antennal segments. The terminal (fused 4th and 5th) rostral segment is pointed or stiletto-shaped. The apterae have a membranous dorsum, with numerous thick, rather short fan-shaped or capitate hairs in 2-3 irregular transverse rows on each segment. The siphunculi are long and slender, sometimes slightly expanded at the apex with a small flange, and the cauda is finger-shaped, tongue shaped or triangular.
There are about 60 species of Pleotrichophorus worldwide, mostly in the Americas, but with seven in Europe. They do not host alternate, but remain all year on members of the Asteraceae, especially those in the tribe Anthemideae. Pleotrichophorus aphids are not attended by ants.
Pleotrichophorus chrysanthemi (Bristly chrysanthemum aphid) Cosmopolitan where chrysanthemums grown
Adult apterae of Pleotrichophorus chrysanthemi (aphid top-right in second picture below, the others are immature) are pale green to yellowish, with longitudinal bands of light wax dusting which give the appearance of darker green median and pleural lines. The apices of their antennae, tibiae and siphunculi are dusky, and the tarsi are dark. The antennae are longer than their body, with a very long terminal process, 5-9 times the length of the base of antennal segment VI (cf. Coloradoa rufomaculata, which has antennae shorter than the body). The head has antennal tubercles, and a moderately-developed median frontal tubercle, all bearing capitate hairs. The rostrum reaches to just past the second coxae, and the apical segment is narrow and acuminate (=tapers to a point). The abdomen has a membranous dorsum bearing many strongly capitate hairs (cf. Coloradoa rufomaculata, which has fan-shaped dorsal hairs). The siphunculi are pale with a dusky apex, very thin, about as long as antennal segment IV, and with no polygonal reticulation (cf. Macrosiphiniella sanborni, which has a zone of polygonal reticulation on the siphunculi). The cauda is pale, rather long and thick, with 3 hairs. The anal plate is slightly darkened, rounded, with a few long hairs. The body length of adult apterae is 1.8-2.4 mm. Immatures (most aphids in pictures below) are very similar to the adult, but have a triangular rather than elongate cauda.
Images above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka (accessed 12/2/20).
The alate viviparous female (not pictured) is pale yellowish to pale green, with a brown head and thorax, and paired dusky dorsal intersegmental markings. The antennae have 10-18 secondary rhinaria in a line along the whole length of segment III.
Pleotrichophorus chrysanthemi are monoecious on the undersides of leaves of florists' chrysanthemums (Dendranthema). They are entirely anholocyclic, and no sexual forms have been found. The 'species' is thought to have arisen quite recently as a clone of Pleotrichophorus glandulosus able to feed on Dendranthema. Pleotrichophorus chrysanthemi is found in most parts of the world where chrysanthemums are grown.
Pleotrichophorus glandulosus (Bristly mugwort aphid) Europe, North America
Adult apterae of Pleotrichophorus glandulosus are yellowish white or greenish, sometimes with a pale green median stripe (see first picture below) (cf. Pleotrichophorus duponti which is dull greyish green with green transverse stripes). The antennal tubercles are fairly low with divergent inner faces. The antennae and legs are mainly pale with only the apex of the fifth antennal segment, the base of the sixth antennal segment, and the tarsi dark. The antennae have a very long terminal process. They have numerous thick, short capitate hairs hairs on the dorsum in 2-3 transverse rows on each segment. The siphunculi are long and slender, cylindrical over most of the length but slightly expanded at the tip with a small flange. The cauda is finger shaped. The body length of the adult Pleotrichophorus glandulosus aptera is 1.4-2.6 mm.
The bristly mugwort aphid lives on the undersides of the lower leaves of mugwort (Artemisia vulgaris). It can also be found on other Artemisia species and corn chamomile (Anthemis arvensis). Sexuales are produced in autumn with eggs laid on the leaf undersides. Pleotrichophorus glandulosus is found over most of Europe including Britain, and has been introduced to North America.