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Drepanosiphum platanoidis (= platanoides)
Common Sycamore AphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:The alate adult female Drepanosiphum platanoidis has a yellow-brown head and thorax with darker brown markings, and a pale green abdomen with or without variably developed dark cross-bars. If cross-bars are present, these are never restricted to abdominal tergites 4-5. 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 3.2-4.3mm. Drepanosiphum platanoides is an incorrect, but commonly used, synonym for Drepanosiphum platanoidis.
The first picture shows an alate vivipara of Drepanosiphum platanoidis which developed in May. Note the yellow-brown head and thorax with darker brown markings. It has well-marked cross-bands which are not restricted to abdominal tergites 4 and 5. The second picture shows an alate vivipara of Drepanosiphum platanoidis which developed in mid-summer (late June). There are no cross-bands and the aphid is generally paler.
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 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 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 in the second image. Fundatrices maturing early often lack any lack melanic pigmentation as in the second picture, although those that mature later are cross-banded.
This picture shows a female fundatrix depositing a nymph. She reproduces parthenogenetically and viviparously. The nymphs 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. This diapause is thought to be induced by high population density of the aphid combined with a poor nutritive status of the leaves (Dixon, 1963 , 1966 ). 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 - on walnut (Juglans regia). This aphid species is not known to reproduce on any tree other than sycamore, but perhaps it can use other species as 'emergency' hosts to to keep them alive when densities get too high on sycamore.
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 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 Discritulus 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 .
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, or wingless oviparae, as in the second image. 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 in the first image. The second image shows an oviparous female which has laid the last of her eggs on the leaf - and then died. 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 ).