Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Mugwort gall aphidOn this page: Identification & Distribution Biology & Ecology Galls Natural enemies Other aphids on the same host
Identification & Distribution
The aphid Cryptosiphum artemisiae produces, and lives within, large deep red globular leaf galls on mugwort (Artemisia vulgaris, see first picture below). The adult apterae are almost globular, dark red to brownish black, and powdered with greyish wax (see second picture below). The head, antennae, legs, tergite 8 and cauda have brownish pigmentation. The antennae are only about 0.25 times the body length with a terminal process that is 0.3-0.7 times the length of the base of the last antennal segment. Like most other Artemisia feeding aphids, the terminal fused segment of the rostrum, (RIV+V), is acutely pointed with concave sides. The siphunculi are reduced to very small pores which are hardly visible, and the cauda is broadly rounded. The body length of adult Cryptosiphum artemisiae apterae is 1.1-1.9 mm.
First image above copyright Gansucha, all rights reserved.
The Cryptosiphum artemisiae alate is also dark red to black, and is covered in wax although less thickly than on the aptera. Its antennae are about 0.5 times body length, and segment III has about 15 secondary rhinaria along the entire segment.
The images below show an apterous adult, and an alate, Cryptosiphum artemisiae in alcohol.
Cryptosiphum artemisiae feeds all year round on mugwort (Artemisia vulgaris) or rarely on field wormwood (Artemisia campestris) forming red leaf galls. Oviparae and alate males are produced in September to October. The mugwort gall aphid is found throughout Europe and Asia.
Biology & Ecology
Until recently we had never found the galls of Cryptosiphum artemisiae on mugwort, despite having found many of the other aphid species found on this plant (see below). The pictures of the gall shown in the first image above and the one below were generously provided by Victor Finchuk (Gansucha) from Ukraine.
Image above by permission, copyright Gansucha, all rights reserved.
These galls are a bright crimson red and appear to be fairly young, recently formed galls. The browny pink galls below are some we found ourselves for the first time on mugwort growing on the old (abandoned) hoverport site at Pegwell Bay in Kent.
The galls covered a large part of the two or three affected plants growing together in a clump, and they were clearly rather old galls. We do not know whether the colour difference simply reflects difference in age of the Ukrainian and English galls, or represents part of the (geographic? inherent?) variability in colour of these galls. Certainly there were very few aphids left alive in the galls we found - one of the few adult apterae is shown in the picture below.
There were however several wine-red immature alatae present in the galls, which soon moulted to adult alatae.
The pictures above show a fourth instar immature alate from one of the galls, and a mature alate about to take off from the mugwort plant.
Cryptosiphum artemisiae is quite unusual in that it has a specific predator, namely the larva of the mugwort hoverfly (Triglyphus primus). The fourth instar larva of Triglyphus primus (shown below) is quite distinctive with large orange-brown respiratory horns (image left), coloured light creamy-green over much of the body with a pinkish hue over the mid-dorsal area.
The adult Triglyphus primus is small and black. It is distinguished by having abdominal tergites II and III very large and tergite IV very small and inconspicuous. On the legs only the 'knees' and metatarsi are pale as can be seen in the picture below of a mature male.
The picture below shows a newly emerged teneral female - the teneral is brown but the mature female is black like the male.
Triglyphus primus is generally considered scarce or rare over much of Europe, although it can usually be readily found wherever galls of its chosen prey, Cryptosiphum artemisiae are present. Falk (2019) notes that the mugwort hoverfly is found most often on post-industrial land - and indeed our find of Cryptosiphum artemisiae and its predator was on the derelict site of the Pegwell Bay hoverport in Kent.
Triglyphus primus was not the only occupant of the galls of Cryptosiphum artemisiae that we found. The pictures below show another aphid/coccid predator, a coccinellid larva, most likely a Rhyzobius species.
Rhyzobius are best known as coccid predators, but on this occasion they were apparently predating the (similarly waxy) Cryptosiphum aphids.
There were other prey, such as numerous Collembola, available for the above predators, especially in the older galls where there were few remaining aphids.
Other aphids on same host:
Cryptosiphum artemisiae has been recorded from 20 species of Artemisia.