Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Waxy willowherb aphidOn this page: Identification & Distribution Biology & Ecology: Life cycle Colour Natural enemies Other aphids on the same host Damage & Control
Identification & Distribution:The adult aptera of Aphis epilobiaria is a reddish-brown to blackish-brown or blackish green, but the colour is mostly masked by a striking pattern of dense pleural wax bands (see first picture below). These converge on the thorax and posterior tergites to occupy most of the width of the dorsum, leaving a spindle-shaped area of the mid-dorsum without wax. The abdominal dorsum of the apterous Aphis epilobiaria is membranous with only a dusky narrow band across tergite 8 and sometimes 7. There are small marginal tubercles on tergites 1 and 7. The apical rostral segment (RIV+V) is 1.3-1.6 times the length of segment II of the hind tarsus and has 6 or more subsidiary hairs. The second tarsal joint is almost entirely smooth (cf. Aphis epilobii where it is ridged). The siphunculi are 1.0-1.6 times the length of the cauda and often bear a few fine hairs. The siphunculi are usually quite pale, sometimes a little dusky. The cauda is quite dark. The body length of apterae is 2.2-2.7 mm.
The alate viviparous Aphis epilobiaria (see second picture above) is reddish brown and usually has postsiphuncular and small marginal sclerites but no dorsal cross bands in front of the siphunculi. The ovipara is reddish brown or greenish black with the hind tibia more or less distinctly swollen on the basal half.
The waxy willowherb aphid does not host alternate. Sexual forms occur in autumn. It feeds on the shoot and flowers of the great willowherb (Epilobium hirsutum) and on other Epilobium species including marsh willowherb (Epilobium palustre), spear-leaved willowherb (Epilobium lanceolatum) and square-stalked willowherb (Epilobium tetragonum). Aphis epilobiaria is not usually ant attended. It is known from Britain and a few western European countries.
Biology & Ecology:
The commonest food plant of Aphis epilobiaria is great willowherb (Epilobium hirsutum), a tall perennial plant with hairy stems and leaves and purple-pink flowers. It has glandular trichomes which contain flavonoids (polyphenolic plant, and fungus, secondary metabolites). The first picture below shows a flowering great willowherb with a colony of the waxy willowherb aphid on the main flower stems. The second picture below shows a colony of Aphis epilobiaria on the flower stem of another willowherb species, the marsh willowherb (Epilobium palustre).
The picture below shows a group of reddish-brown immature Aphis epilobiaria.
There is some evidence that Aphis epilobiaria is currently attempting to colonize another plant genus - evening primrose (Oenothera species). Turcinaviciene et al. (2006) reported that parthenogenetic apterae and winged females, as well as oviparae and males of Aphis epilobiaria were found on Oenothera in the Czech Republic. The colonies were thriving and winter eggs were deposited in great numbers. However, the fundatrices were unable to feed on Oenothera in spring.
The dramatic black and white coloration of this aphid is very reminiscent of the coloration of Macrosiphoniella absinthi As with that species, we have to ask whether this a case of aposematic coloration (black and white are commonly-used warning colours) or a form of crypsis: either pattern blending in amongst the flower head, or disruptive coloration - where a block of highly contrasting coloration and sharp boundaries prevent a predator from detecting or recognizing the prey's outline (Caro, 2009 ).
Their black and white coloration could of course have a dual function, as Ruxton (2002) suggested for zebra stripes - cryptic when aphids are amongst the flower heads in low light, and aposematic when exposed on the flower heads. We suggested something similar for Tuberolachnus salignus in our August blog.
Natural enemiesThere are only a few references to Aphis epilobiaria being attacked by parasitoids. Takada (1998) gives Aphidius colemani as a parasitoid of Aphis epilobiaria whilst Mescheloff & Rosen (1990), gives Lysiphlebus fabarum. We have found parasitoid mummies of Aphis epilobiaria (see picture of light-brown mummified aphid below), but have not yet identified the species involved.
We have found a syrphid larva predating Aphis epilobiaria (see picture below). Given the larva is dorso-ventrally flattened, it is most likely an Epistrophe species.
Most authorities indicate that Aphis epilobiaria is not ant attended, but we have found a Lasius ant apparently tending Aphis epilobiaria (see picture below).
Other aphids on same host:
Blackman & Eastop list about 33 species of aphids as feeding on willowherbs (Epilobium species) worldwide, and provides formal identification keys.
Of these aphid species, Baker (2015) lists 16 as occurring in Britain: Aphis epilobiaria, Aphis epilobii, Aphis fabae, Aphis frangulae, Aphis gossypii, Aphis grossulariae, Aphis mirifica, Aphis praeterita, Aphis salicariae, Brachycaudus cardui, Macrosiphum euphorbiae, Macrosiphum tinctum, Myzus ascalonicus, Myzus lythri, Myzus ornatus and Myzus persicae - although some only occur on particular species of Epilobium, such as Aphis mirifica and Aphis salicariae on Epilobium angustifolium.