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Californian Maple aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Periphyllus californiensis apterae (see first picture below) are reddish brown to dark olive-green. The length of the antennae is about 0.6 times the body length, with the terminal process about twice as long as the last antennal segment.The broken dorsal cross bands are dark as are the head, pronotum, and siphunculi. The siphunculi are about as long as the second hind tarsal segment. The hind femur and tibia are uniformly dark (cf. Periphyllus testudinaceus where the tibiae have a very pale middle section which contrasts with their dark base and tip). The cauda is broadly rounded with 8-12 hairs. The body length is 2-3 mm.
The Californian maple aphid is not indigenous to Europe (nor to California), but is from East Asia. Periphyllus californiensis has proved highly invasive and has spread to Europe, North America, Australia and New Zealand on planted Asian ornamental maples such as smooth Japanese maple (Acer palmatum) and downy Japanese maple (Acer japonicum).
Biology & Ecology:
The Californian maple aphid infests maple trees the whole year round. The overwintering eggs hatch in spring before budburst. Wang (2006) found that egg hatching of the maple aphid is affected by microhabitat and date of oviposition. The fundatrices can stay on the bud scales before bud growth begins, but they do not moult to second instar until the buds start to swell. (Furuta 1990 ).
These fundatrices give rise to one or more generations of winged or wingless spring generations by parthenogenesis, the aphids feeding on the growing buds, leaves, shoots and flowers (see picture below of developing colony).
The number of fundatrices on early budding trees is higher than on late budding trees (Furuta, 1984 ). The winged progeny then disperse to late budding tees where they reproduce in turn.
These winged adults can produce two forms of nymphs: either normal nymphs, or aestivating nymphs (misleadingly known as dimorphs) see picture below. Which form of nymph they produce depends upon their host tree condition. As leaves expand, the soluble nitrogen content in the phloem declines, and the aestivating nymphs are produced.
The aestivating nymphs of Periphyllus californiensis (close-up below) are remarkable. They are quite different in appearance from usual nymphs, being very flattened with foliate (leaf-like) marginal hairs. They have just two series of abdominal plates (spinal and marginal) in contrast to Periphyllus testudinaceus which has spinal, marginal and pleural plates.
They suffer very high mortality over summer (Furuta, 1985 ) although mortality of the dimorphs on key-fruits is slightly less than that on leaves. No density-dependency has been detected in the mortality. Sleeving cage tests indicated that the mortality is caused mainly by (unidentified) predators. On those trees on which many dimorphs have been laid in the spring, a few dimorphs remain and become active in autumn.
Periphyllus californiensis utilizes the key (winged) fruits of maple in October, the leaves in November, and the twigs in December. Winged females appear in November and disperse to spread the autumnal population over many trees. Many winged females of Periphyllus californiensis produce offspring on maple trees whose foliage is orange yellow, while only a few produce offspring on the trees whose foliage is red. (Furuta, 1986. ) Hence the autumnal colour of maple trees is an important factor which keeps some trees free from aphid infestation in autumn. The offspring develop to oviparae which lay the overwintering eggs.
Damage and control
Aphid infestations of Japanese maples are most common in the spring. Leaves with Periphyllus californiensis may become wrinkled or curled, and flowers that appear later in the year may be deformed. Heavy infestations can lead to large amounts of honeydew which may be covered with unsightly mould. The aphids can also transmit virus diseases to the tree. The aphids are best controlled by releasing or encouraging natural predators and parasitoids. Periphyllus californiensis can also be reduced in numbers by spraying insecticidal soap, neem oil or narrow range oil in a spray solution.