Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Stonecrop aphidOn this page: Identification & Distribution Biology & Ecology: Taxonomy Life cycle Ant attendance Natural enemies Other aphids on the same host
Identification & Distribution:
Aphis sedi apterae are small and dark green to blackish green with no wax powdering. Their dorsal abdominal sclerotic pattern is limited at most to dusky bands across tergites 7-8. The siphunculi of Aphis sedi are dark, but the antennae and legs have conspicuous pale sections (see first picture below). The siphunculi are 0.8-1.5 times the length of the cauda which is short, blunt and rather dark, only a little paler than the siphunculi (cf. Aphis gossypii where the cauda is usually pale/dusky, markedly paler than the siphunculi). The body length of Aphis sedi apterae is 1.0-1.6 mm.
Aphis sedi, which is monophagous on stonecrops (Sedum) and other Crassulaceae, is very similar to the polyphagous Aphis gossypii, from which it is thought to have evolved. There are nevertheless some distinguishing morphological characteristics. The antennal terminal process of Aphis sedi is 1.6-2.3 times the base of the sixth antennal segment (cf. Aphis gossypii which has the terminal process 2.1-3.2 times the base of the sixth antennal segment). The fused apical rostral segment (RIV+V) of Aphis sedi is 1.04-1.20 times the length of the second hind tarsal segment (HT2) (cf. Aphis gossypii where RIV+V is 1.00-1.57 times the length of HT2.)
The Aphis sedi alate (see second picture above) has a relatively strongly developed dorsal abdominal pattern with (on larger specimens) large marginal and postsiphuncular sclerites, broad bands across tergites 6-8 and variably developed bars on some or all of tergites 1-5. The alate has 4-12 secondary rhinaria on the third antennal segment and 0-3 rhinaria on the fourth antennal segment.
The stonecrop aphid does not host alternate. Sexual forms occur in autumn. It feeds on various stonecrops (Sedum spp.) forming large colonies up young stems, in flower heads or under leaves. It is attended by ants and causes distortion of the infested shoot. Aphis sedi occurs throughout Europe and parts of Asia as well as the eastern USA.
Biology & Ecology:
Aphis sedi is thought to have developed from Aphis gossypii by isolation on a different host, namely Sedum spp. (Kring (1955)). Coccuza et al. (2009) found that using mitochondrial DNA Aphis sedi was indistinguishable from Aphis gossypii, but Lagos-Kutz et al. (2014) detail the biological and morphological differentiation of the two species.
Aphis sedi lives all year round on stonecrop. It reproduces parthenogenetically through the warmer months, and then in autumn apterous males mate with the females to produce the overwintering eggs. In the sub-family Aphidinae, most male aphids are alate and most oviparous females are apterous, so apterous males are unusual. Kring & Kring (1991) showed that some of the wingless males had alate-like bodies and some had aptera-like bodies. Alford (2012) reports it on aerial roots of various members of the Crassulaceae. The picture below shows a colony on the flower head of Sedum.
Aphis sedi is sometimes, but not always, attended by ants. Mifsud (2008) found Aphis sedi in Malta on Sedum sediforme attended by the ant Crematogaster scutellaris. We found Lasius ants active around an aphid colony on biting stonecrop (Sedum acre) (see picture below).
However, despite the fact that we observed the colony and ants for several minutes, we saw no evidence of the ants actively tending the aphids for honeydew. Instead the ants were more interested in the stonecrop flowers, possibly for the nectar, than they were in the aphids.
We have seen rather little evidence of parasitism or predation in the colonies we have looked at, with the exception of predation by spiders on aphid populations on the flowering heads of Sedum rupestre (see picture below).
Other aphids on same host:
Blackman & Eastop list 4 species of aphid as feeding on Angelina stonecrop (Sedum rupestre) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists all 4 as occurring in Britain (Show British list).
Damage and control
Wilcaniec & Piekarska-Boniecka (2008) reported Aphis sedi infesting as many as ten different species of the Sedum genus in the collection. Significant inhibition of plant growth was observed on the stonecrops heavily infested by aphids.
Raupp et al. (1994) attempted augmentative biological control of Aphis sedi using larvae of Chrysoperla carnea (common green lacewing) and Chrysoperla rufilabris. Lacewing larvae did not appear to have an impact on aphid density on stonecrop plants. One week after the release of lacewings, there was no significant difference in aphid numbers between treatments. The reason for the lack of efficacy was unclear. It was thought that ants could play an important role in limiting the efficacy of biological control agents by protecting the aphids.