Genus Cavariella [Macrosiphini]
Small to medium-sized green, straw-coloured or ochreous-reddish aphids. The body of apterae is rather elongate and a little flattened. The antennal tubercles are rather low, about the same height as the median tubercle. The antennae are rather short in the apterae but longer in alatae. The cuticle in apterae is strongly sclerotic, but not pigmented. The siphunculi are cylindrical or clavate with a small rim at the apex. They are very distinctly longer than the cauda which is rather blunt. The supracaudal process on the precaudal tergite is usually diagnostic for the genus. Winged forms have a trapezoidal black patch on the dorsum in front of the siphunculi.
There are 31 species in the world. They host alternate from various willow (Salicaceae) species as the primary host to various umbellifers (Apiaceae) as the secondary host. Most species retain a sexual stage in the life cycle. They are not attended by ants. The species are difficult to differentiate from photos unless special attention is paid to getting good images of the siphunculi, the supracaudal process and the antennae.
Cavariella aegopodii (Willow - carrot aphid)
The apterae are small and greenish or reddish. The tips of the antennae and apices of the legs are brownish. The antennae are about 0.4 times the body length, with the terminal process about 0.85-1.5 times the basal part of segment VI. The siphunculi are swollen and about twice as long as the cauda. The supracaudal process is 0.75-1.05 times the cauda, broadest at the base and oblong triangular to conical. The body length of apterae is 1.5-2.8 mm.
The willow-carrot aphid host alternates from willows (Salix spp) to umbellifers (Apiaceae). The preferred primary hosts are crack willow (Salix fragilis) and white willow Salix alba, although some Willow species seem only to be colonized in spring, by winged forms from populations which have overwintered parthenogenetically. Preferred secondary hosts are cultivated umbellifers such as carrots (Daucus carota) and fennel (Foeniculum vulgare) and several wild umbellifers. It is widespread throughout temperate and warm temperate parts of the world.
Cavariella archangelicae (Willow - angelica aphid)
The adult apterae are green or yellowish. The antennae are 0.35-0.39 times the length of the body and the terminal process is1.5-2.0 times the base of the last antennal segment. The siphunculi are more than twice as long as the cauda with the distal half somewhat swollen in a nearly symmetrical way. The supracaudal process has a broad basal part and is tongue-shaped about 0.7-1.0 times the length of the cauda. The body length of apterae is 1.5-2.6 mm.
The willow - angelica aphid host alternates from willow (Salix spp.) to angelica (Angelica). Sexual forms occur in October. Its distribution is cosmopolitan.
Cavariella pastinacae (Willow - umbellifer aphid)
Adult apterae are rather light shiny green with appendages pale except for the base of antennal segment VI and the tarsi which are dark. The antennae are about 0.45 times the length of the body and the terminal process is 3.0-4.0 times the base of the last antennal segment. The siphunculi are 2.3-3.0 times as long as the cauda and are slightly swollen towards the tip. The supracaudal process is broadly tongue-shaped,with a flat apex and is 0.5-0.8 times the length of the cauda. The body length of apterae is 1.8-2.9 mm. The alate has a dark abdominal patch formed by more or less fused cross bands on tergites III-VI. The antennae, cauda, supracaudal proces and distal halves of siphunculi are dark.
The willow - umbellifer aphid host alternates between willows (Salix spp.) and some umbellifers mainly hogweed (Heracleum), wild parsnip (Pastinaca) and Angelica. Common over most of Europe and in North America.
Cavariella theobaldi (Willow - parsnip aphid)
Adult apterae are green with the tips of the antennae and apices of the legs dark. The antennae are 0.50 times the length of the body and the terminal process is 2.1-3.5 times the base of the last antennal segment. The siphunculi are more than twice as long as the cauda and are cylindrical or tapering from base to the apex; they are not swollen (distinguishes from Cavariella pastinacae which has the siphunculi slightly swollen towards the tip). The supracaudal process is more or less quadrangular and small, about 0.3-0.7 times the length of the cauda. The body length of apterae is 1.8-2.8 mm. The alate has a dark abdominal patch formed by more or less fused cross bands on tergites III-VI. The antennae are dark and the siphunculi are brownish.
The willow - parsnip aphid host alternates between willows (Salix spp.) and some umbellifers mainly wild parsnip (Pastinaca) and hogweed (Heracleum). Common over most of Europe and in North America.
- Dixon, A.F.G. & Thieme, T. (2007). Aphids on deciduous trees. Naturalist's Handbooks 29. Richmond
- Heie, O.E. (1980-1995). The Aphidoidea, Hemiptera, of Fennoscandia and Denmark. (Fauna Entomologica Scandinavica) E.J. Brill, London
David Fenwick,11 July 2013, Cavariella pastinacae
Does this appear to look like Cavariella pastinacae to you?
I first thought C. theoboldi, but the siphunculi appear to be slightly swollen, although on juveniles they look quite straight.
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Although my views may change on more reflection/examination, on Cavariella pastinacae versus C. theobaldi, it's very difficult in photos because both occur commonly on Heracleum, and the precise angle can change the appearance of the siphunculi. I'm going to do some slide preps soon to try to confirm a few provisional IDs. You may well get mixed species colonies on Heracleum.
Starting to know exactly what you mean! LOL. Finding some quite tricky indeed, can probably get to genus level on some but futher than that it's like wading through treacle. It actually goes to show how good your site is as it's without a doubt the best reference point I can find for many.
Yes and of course other species that will feed on most things. C. theobaldi hasn't been recorded in Cornwall but I guess it's here. Lots of records for Cavariella pastinacae but mostly from one person, which makes me wonder a bit!
David Fenwick, 4 August 2013, Aphid on Fennel
This fennel had either naturalised, or was planted, in [Bolitho Park] along the promenade at Wherry Town.
Interesting one this.
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I'm fairly certain your fennel aphid is Cavariella aegopodii - the willow-carrot aphid.
Antennae 0.4x body length, swollen siphunculi with the supracaudal process about as long as the cauda.
We find it every year on fennel, often heavily pararasitized.