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"It has long been an axiom of mine that the little things are infinitely the most important" |
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Macrosiphoniella artemisiaeMugwort aphidOn this page: Identification & Distribution Biology & Ecology Colour Ant attendance Defensive behaviour Natural enemies Other aphids on the same hostIdentification & DistributionMacrosiphoniella artemisiae apterae are of moderate size, greyish-green (or sometimes pinkish see below) and wax powdered. Their antennae and legs are mostly black, except for the base of antennal segment III and the basal part of the front femur which are brown. The siphunculi and cauda are entirely black (cf. Macrosiphoniella oblonga, which has a green cauda). The body hairs are not placed on dark scleroites (cf. Macrosiphoniella millefoli, which sometimes occurs on mugwort, but has numerous dark scleroites). The sclerites in front of the siphunculi are very pale and hardly visible. The siphunculi are 0.6-0.9 times the cauda length (cf. Macrosiphoniella oblonga, which has siphunculi 1.0-1.4 times longer than the cauda). The body length of Macrosiphoniella artemisiae apterae is 2.3-3.6 mm.
The Macrosiphoniella artemisiae alate is much like the aptera but the marginal sclerites are well developed. The clarified slide mounts below are of adult viviparous female Macrosiphoniella artemisiae : wingless, and winged.
Micrographs of clarified mounts by permission of Roger Blackman, copyright AWP all rights reserved. The mugwort aphid lives on the upper parts of mugwort (Artemisia vulgaris) especially amongst the flowers. Sexual forms occur in the autumn (apterous oviparae and winged males). The species overwinters as eggs. Macrosiphoniella artemisiae is found in Europe, north Asia, North Africa and North America. Biology & EcologyColourMost of the literature describes adult apterae of Macrosiphoniella artemisiae as being greyish green and wax dusted (Heie, 1980-1995, Blackman, 2010) or "green covered with white wax so the colour appears pale green with a darker longitudinal stripe" (Jensen et al., 2020). We have found that colour in UK populations is rather more variable than that, with various pink forms present especially later in the year. We first encountered pink forms in 2015 and then again in four of the following five years. Some are uniformly pink, but many are variegated pink and green over the dorsum (see picture below).
Pink forms tend to occur in groups, so one colony will be pink and or pink/green variegated and the other green. The group shown below included pink immature oviparae (with swollen greyish tibiae).
Other colour forms of Macrosiphoniella artemisiae have been reported including a 'mutant yellow form' in Kent (Blackman, 2010). Ant attendanceLike all aphids, the mugwort aphid exudes honeydew as an excretory product - a droplet can be seen below.
The honeydew produced by Macrosiphoniella aphids tends to have little or no melezitose - a sugar specially attractive to ants (Fischer & Shingleton (2001)) - so Macrosiphoniella artemisiae is not tended by ants. Defensive behaviourThere is no information in the literature on whether Macrosiphoniella artemisiae has any specific defensive behaviour against parasitoids, although 'kicking' is the most likely.
However, Ghish & Inbar (2006) have described defensive behaviour in response to vibration such as may be caused by a mammalian herbivore which may consume both vegetation and aphids - namely the aphids may drop from their host plant to the ground. Experimentally, vibration of the apical bud induced dropping in 36% of the colony members. Dropping rates were highest in mature aphids (63%). Relocation was remarkably efficient with nearly all mature aphids that were dropped 13 cm from the plant, finding their way back in about 40 seconds. Location was apparently based on visual cues. The authors concluded that Macrosiphoniella artemisiae is capable of visually discriminating between host and non-host targets and apparently does not react to volatiles emitted from the plant. Natural enemiesThe mugwort aphid is often attacked by parasitoids. We are not certain of the identity of parasitoid that mummified the aphid below, but it is most likely to be Aphidius absinthii.
Aslan et al. (2004) found the parasitoid Aphidius absinthii parasitizing Macrosiphoniella artemisiae in Turkey. Kavallieratos et al. (2004) recorded Aphidius absinthii, Binodoxys centaureae and Lysaphidus arvensis parasitizing Macrosiphoniella artemisiae in Serbia. Other aphids on same host:Macrosiphoniella artemisiae has been recorded from 17 Artemisia species. Blackman & Eastop list 73 species of aphid (including 28 Macrosiphoniella species) as feeding on mugwort (Artemisia vulgaris) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 27 as occurring in Britain (Show British list).
Macrosiphoniella artemisiae is commonly found on the flower heads in mixed species populations with other species of aphids - as illustrated with a nymph of Macrosiphoniella oblonga below.
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