Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Drepanosiphum platanoidis (= platanoides)
Common Sycamore AphidOn this page: Identification & Distribution Biology & Ecology: Colour Life cycle Natural enemies Other aphids on the same host
Identification & Distribution
Immature Drepanosiphum platanoidis (see first picture below) are pale green with long cylindrical siphunculi and red eyes. All adult viviparae are alates. The alate female Drepanosiphum platanoidis has a yellow-brown head and thorax with darker brown markings. The abdomen is usually pale green, although there is a less common red form which occurs from summer to autumn. If the alate develops in spring or autumn, it has variably developed dark cross-bars (see second picture below), but if it develops in mid summer, there are no cross-bands and the aphid is generally paler (see third picture below). The dark cross-bars are never restricted to abdominal tergites 4-5 (cf. Drepanosiphum acerinum, which has one or two short brown bars on abdominal tergites 4-5 only). The antennae are brown, and the siphunculi are pale with a brown tip. The forewing has no black spot at the tip nor one at the outer end of the pterostigma; the pterostigma is defined by two longitudinal brown stripes. The body length is 3.2-4.3 mm.
Note: Drepanosiphum platanoides is an incorrect, but commonly used, synonym for Drepanosiphum platanoidis.
The common sycamore aphid is found on the undersides of leaves of sycamore (Acer pseudoplatanus). It is also recorded from many other Acer species, as well as a wide variety of other trees which are only visited on a casual basis. Sexual forms occur in September-November. Drepanosiphum platanoidis is common or abundant on sycamores wherever they are grown in Europe, central Asia, north Africa, Australia, New Zealand, USA and Canada.
Biology & Ecology:
The abdominal ground colour of Drepanosiphum aphids is determined by body fluids and fat body visible through the cuticle. The aphids that develop from the overwintering eggs in spring (the fundatrices) are always green often with bold black transverse bars on the abdomen. The offspring of the fundatrices, which reach maturity in summer, are always very pale with no black bars and with paired white wax patches on the abdominal segments. They are also usually green as in the picture below.
However, a small percentage (up to 17%) of the summer adults are red rather than green (see picture below).
Red adults give birth only to red nymphs so that within the population clones of red aphids develop. This means that red aphids continue to be produced in September but with the black abdominal bars that are also present on the green aphids in spring and autumn.
Dixon (1972) investigated the mechanisms by which the red forms develop. He found that red forms can be induced to develop in the third generation if the aphids are kept at high temperatures. First generation adults (which are always green) cannot readily be induced to produce red offspring, whereas later generations are more easily induced to do so. This suggests there is an interval timer mechanism controlling the develoment of red forms similar to the mechanism which restrains the appearance of sexual morphs early in the year. The action of this restraining mechanism and the cool conditions in spring result in the red forms first appearing in summer. In addition to temperature, overcrowding is also thought to induce the development of red forms. Little more is known about the red form of the sycamore aphid but it seems to be more active than the green form, possibly develops faster, and is possibly better adapted to withstand the high temperatures and overcrowded conditions prevalent in summer.
The eggs of Drepanosiphum platanoidis are laid on rough areas of sycamore bark in the autumn, and hatch in the following March. Hatching is well synchronised with the average time of bud burst, so the young nymphs are able to exploit highly nutritious young foliage as it emerges from the buds.
The picture above shows a young nymph of Drepanosiphum platanoidis on a sycamore bud in March.
The two pictures above show first and second instar nymphs of the common sycamore aphid aggregating on the bursting buds of sycamore. Those aphids that hatch immediately prior to budburst grow more rapidly and achieve a greater size than those that emerge after budburst (Dixon, 1976).
The nymph shown in the first picture above has reached the fourth instar and the developing wing buds are visible. These nymphs mature into adult female winged fundatrices, one of which is shown below.
The nymphs produced by the fundatrix mature in June and July, usually into very pale alates such as shown in the picture below. These alate aphids show a remarkable uniformly-spaced pattern of aggregation on the undersides of sycamore leaves.
Sycamore aphids aggregate on particular leaves, but maintain a minimum space between each other (Kennedy & Crawley, 1967) giving the spaced-out pattern. Dixon & Logan (1972) showed that the spacing is partly dependent on the density of aphids on the leaf. Very few nymphs are present at this time of year, because most of the adults undergo a reproductive aestivation or diapause.Note the globules of honeydew (sugar-rich aphid excretion) on the leaf - unlike some aphid species, Drepanosiphum platanoidis is not attended by ants feeding on this secretion.
Not all aphids remain on the same tree throught their life. Two types of flights have been distinguished for sycamore aphids: trivial flights and migratory flights (Dixon, 1969). Both types are more common when there are high densities of fourth instar nymphs. Trivial flights occur when the aphid changes its position within the canopy of the tree, or disperses to adjacent trees. Such movement is not restricted to alates and both alates and nymphs can often be found in large numbers on adjacent unsuitable hosts.
The image above shows a common sycamore aphid nymph living - and apparently feeding - not on sycamore, but on walnut (Juglans regia)! This aphid species is not known to reproduce on any tree other than sycamore, but perhaps it can use other plant species as a reserve host to keep them alive before the alatae migrate to another sycamore tree.
By August the (previously aestivating) alate females start to produce nymphs, often after having first migrated to another tree. Some of these nymphs develop into parthenogenetic females, but over time an increasing number instead develop into either winged males, as in the first image below, or wingless oviparae, as in the second image below.
This ovipara is dark green with dark bands, but colour varies from light green to dark brown and bars may be present or completely absent. The end of the abdomen of the ovipara is extended like an ovipositor.
By October most of the sycamore aphid population is comprised of winged males and oviparous females and mating pairs can often be seen on the leaves, as shown above.
Normally the eggs of Drepanosiphum platanoidis are laid in crevices in the bark more than 50 cm from a terminal bud (Dixon, 1976).
Freshly laid aphid eggs are pale yellow to green, but soon darken to shiny black. They are aggregated on rough bark, with competition among oviparae for the best oviposition sites. Egg mortality varies from 65-85% with the greatest mortality in late winter (Wade, 2002).
Predators and parasitoids are not often seen early in the year, but from July onwards they can be very common amonst sycamore aphids. These two images show the aphid 'mummy' resulting from attack by the specialist braconid parasitoid Dyscritulus planiceps (sometimes wrongly named Discritulus planiceps). The parasitoid larva feeds in the body of the aphid and then pupates under the aphid, but in a flat disc rather than a tent as Praon species do. Macroscopically these can resemble aphids attacked by Entomopthora fungus, but close examination shows no fungal hyphae on these aphids.
The first image shows the adult braconid Dyscritulus planiceps which emerged from the mummy of a sycamore aphid shown above. Another specialized parasitoid is the aphelinid Aphelinus thomsoni which produces a black mummy shown in the second image.
Predators of sycamore aphids are also numerous. The first image shows a syrphid larva found feeding on Drepanosiphum platanoidis in October. The second image shows an anthocorid bug Anthocoris nemorum attacking a mummy caused by yet another specialized parasitoid - either Monoctonus pseudoplatani or Trioxys cirsii. Dixon and Russell (1972) reported that anthocorids regularly feed on mummified aphids, not least because they are much easier to catch than live active aphids. Other predators include the two-spot ladybird (Adalia bipunctata), lacewing larvae (Chrysopa carnea) and wood ants (Formica rufa). Skinner & Whittaker (1981) demonstrated that predation of this species by wood ants resulted in significant depression of the population compared to when ants were excluded from shoots. Hence the relationship between wood ants and aphids on sycamore is not always beneficial to the aphids as it was with Periphyllus acericola.
Sycamore aphids are not attended by ants, but vespids can often be found gleaning the honeydew from the leaves (see picture below).
Other aphids on same host:
Drepanosiphum platanoidis has been recorded on 19 Acer species.
Blackman & Eastop list 12 species of aphid as feeding on European sycamore (Acer pseudoplatanus) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 8 as occurring in Britain (Show British list).