Biology, images, analysis, design...
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Identification & Distribution:The aptera is a small to medium sized aphid 1.5 - 2.6mm long with an elongate shape. It is usually pale green with a fine darker green mottling, covered with wax meal. The antennae are quite short, between 0.5 - 0.75 times the body length. The siphunculi are very short, and are thicker and darker towards the apex; they are also flangeless and rounded at apex. The cauda is 1.5 - 3.0 times longer than the siphunculi. The winged form is green with white wax patches on the dorsum of each abdominal segment.
The Mealy Plum Aphid host-alternates between its winter host - Prunus species, mainly plum but also peach, apricot and almond, and its summer host - reeds (Phragmites), Giant Cane (Arundo donax) and some other wetland grasses. Some aphids remain on plum all the year round.
The first image show an aptera of Hyalopterus pruni on Phragmites together with nymphs of various ages. Note especially the wax meal covering and the very short siphunculi which are only visible on the apterae and nymphs because of their dark tips. The second image show several alates of the same species on Phragmites.
Biology & Ecology:
The eggs of this species overwinter on Prunus species. They hatch in April, usually by the white bud stage on plum. They seldom cause much curling of the leaves, but can live inside curls of newly expanding leaves. As the season progresses, colonies can literally 'pave' the underside of the leaves.
The winged forms of this species only start to develop in early June (later than those of other aphid pests on plum, Brachycaudus helichrysi and Phorodon humuli), when they migrate to waterside grasses and reeds. The population on plum continues to increase through July, with the peak of migration to grasses occurring between early July and early August.
Its main summer host is the common reed Phragmites australis although it has been recorded on other grasses. Moericke (1969) demonstrated that Hyalopterus pruni emigrants are attracted to colour in the range orange-yellow-green, but only when these colours are unsaturated tints. This is a specific adaptation to the unsaturated colour of the leaves of Phragmites. Large colonies develop on Phragmites as can be seen below. On the summer host the species exhibits colour polymorphism with two colour forms - green and dark red.
Predators and parasitoids attack the mealy plum aphid on both its winter and summer host. The first image below shows a larva of the invasive harlequin beetle (Harmonia axyridis) on an infested plum leaf in June.
The second image above shows a mummy of Hyalopterus pruni parasitized by the braconid Praon volucre, the dominant parasitoid of this species in Europe. Other parasitoids attacking the mealy plum aphid are Ephedrus plagiator and Aphidius transcaspicus (Starý & Havelka, 2008 ). The ectoparasitic mites Allothrombium triticium and Erythraeus ankaraicus can also be found on Hyalopterus pruni. Bayram & Çobanoglu (2005) found parasitism rates were between 1% and 5%, and suggested that higher parasite loads increased aphid host mortality. Note the mites are true parasites rather than parasitoids as they do not invariably kill the host.
Damage and control
In Europe this aphid is only a pest on its winter hosts, in particular plums. When it occurs in large numbers on young leaves it causes significant feeding damage, but leaf curling only seems to occur when very young leaves are attacked. It combines this damage with excreting honeydew on to lower leaves, which become dark with sooty moulds growing in the resulting sticky film. These fungi reduce the plant's ability to photosynthesise. This species is 'weak' vector of Plum pox potyvirus.
The situation in America is rather different where Hyalopterus pruni is a non-native invasive species. Not only is it a pest on plum, but there is also concern about its effects on its summer host Phragmites australis (the common reed). An aggressive, non-native haplotype (distinct genetic lineage within a species) of Phragmites australis from Europe is invading brackish and freshwater systems in the eastern United States, potentially displacing native haplotypes. Both Lambert & Casagrande (2007) and Park and Blossey (2008) have found significantly higher aphid populations on native haplotypes than on the non-native haplotype. Moreover Lambert & Casagrande (2007) found that aphid feeding caused chlorosis and death of native stems, whilst the non-native plants remained relatively undamaged. There is therefore concern that non-native aphid infestation may indirectly affect the ability of these native plants to compete with non-native plant populations, ultimately contributing to the decline of native haplotypes. The two haplotypes of Phragmites australis have each recently been accorded subspecific status.