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Pear-grass aphid, Brown pear aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Interspecific competition / association Ant attendance Natural enemies Other aphids on the same host Damage & Control
Identification & Distribution
In spring Melanaphis pyraria roll the leaves of its primary host, pear, transversely or diagonal to the mid-rib (see first picture below). This pseudogall may become yellowed or reddened. The dorsal abdomen of the adult aptera on pear is dark reddish brown and has a solid dark sclerotic shield (see second picture below) (cf. Aphis pomi and Rhopalosiphum oxyacanthae, which are both green). There is little or no wax on the dorsum (cf. Dysaphis pyri, which are thickly coated with grey wax meal). The hairs on the antenna and dorsal body are minute, less than half the diameter of the third antennal segment. The siphunculi are dark, about twice their basal width and shorter than the cauda (cf. Dysaphis pyri, which has siphunculi longer than the cauda). The body length of Melanaphis pyraria is 1.3-2.1 mm. Immatures are initially orange, darkening to red-brown as they mature. The alate of Melanaphis pyraria (see third picture below) which migrates to their secondary host, grasses, has a brown abdomen with the dark dorsal shield reduced to a series of transverse dark dorsal bands across the abdominal tergites. The head and prothorax are dark sclerotic.
The appearance of the offspring of those alatae on grasses is quite different, and depends on which grass species is colonised. On oatgrass (Arrhenatherum) the apterae (not pictured) are reddish purple and hide under the deformed leaves. On brome grass (Brachypodium) Melanaphis pyraria (see three pictures below) are smaller, yellow-orange and live dispersed over the leaf blade.
The micrographs below show an apterous adult Melanaphis pyraria, dorsal and ventral, in alcohol.
Melanaphis pyraria host alternates from its primary host pear (Pyrus) to its secondary hosts grasses (including Arrhenatherum, Brachypodium, Holcus, Poa and Triticum). On their primary host they may be attended by ants. On the secondary host the appearance of Melanaphis pyraria differs according to the particular genus of grass colonized - reddish purple on Arrhenatherum, and yellowish on Brachypodium, Poa and Triticum. The pear-grass aphid is widely distributed in Europe, as well as the Mediterranean region, the Middle East and the Caucasus.
Biology & Ecology
Melanaphis pyraria overwinters on its primary host, pear (Pyrus, see first picture below of the fruit) in the egg stage. Pear-grass aphids do not produce a true gall on pear (in other words there is no enlargement and/or proliferation of host cells), but they roll and crumple the leaves to form a pseudogall. These pseudogalls can be very conspicuous on pear trees in spring even without the typical red discolouration (see second picture below).
The youngest nymphs are bright orange turning to red-brown as they mature (see picture below).
The young nymphs are often found aggregated on the young leaves of pear in dense colonies.
As densities on pear increase, so more aphids develop into alatae (see picture below).
The alatae migrate to their secondary host - various species of grasses - where they establish colonies. On oatgrass (Arrhenatherum) the aphids deform the grass blades and hide under the deformed leaves. On brome grass (Brachypodium) they live dispersed over the leaf blade (see picture below).
In late autumn there is a return migration to pear where sexual forms are produced. After mating the oviparae lay overwintering eggs on the twigs and branches of pear trees.
Interspecific competition / association
One might expect the pseudogalls made by a particular aphid species to only contain aphids of that species. But the galls of some aphid species such as the poplar-buttercup gall aphid (Thecabius affinis) may be colonised by other aphid species, in that case by the black poplar leaf aphid (Chaitophorus leucomelas) which takes advantage of the protection and improved nutrient supply offered by the gall. The pseudogalls of Melanaphis pyraria are similarly inhabited by other fruit tree aphids such asRhopalosiphum oxyacanthae (see picture below).
As well as other aphid species, the pear psyllid Cacopsylla pyricola, a notorious pest of pear, can be found feeding within the galls of the pear-grass aphid (see picture below - the psyllid nymph is pale yellow-green with red eyes).
Melanaphis pyraria is usually attended by ants, but only on its primary host (see picture below).
Most of the pear-grass aphid colonies we have found have been attended by the common black ant, Lasius niger (see picture below).
In his review of parasitoids in the Mediterranean area, Stary (1976) records three aphid parasitoids on Melanaphis pyraria - Aphidius uzbeckistanicus, Ephedrus cerasicola and Trioxys angelicae. INRA record Ephedrus persicae as a parasitoid of Melanaphis pyraria. We found the mummy of Melanaphis pyraria shown below on Brachypodium grass. It is most likely an Ephedrus species.
Various aphid predators have been recorded as frequenting pear orchards (for example Youssif (2019) recorded the coccinellids Coccinella undecimpunctata, Coccinella septempunctata, Coccinella 9-punctata, Scymnus syriacus, Scymnus interruptus, Cydonia vicina isis & Cydonia vicina nilotica on pear trees in Egypt infested with Aphis gossypii). However, we have found no records of them feeding on Melanaphis pyraria.
We have only found one species of coccinellid on pear trees with colonies of Melanaphis pyraria, namely the pine ladybird Exochomus quadripustulatus (see picture above), although given the feeding preferences for this species it is more likely that it was feeding on coccids also present on the trees.
Other aphids on same host:
Melanaphis pyraria has been recorded from 3 Pyrus species (Pyrus amygdaliformis, Pyrus communis, Pyrus korshinskyi).
Damage and control
Basilova & Rakauskas (2012) review the damage to pear caused by Melanaphis pyraria. The fundatrices and the first generation of apterous viviparous females do not cause pear leaf deformations, but further generations feeding on the undersides of young pear leaves cause transverse to mid-rib leaf rolling or curling, and also cover the leaves with honeydew. Under favourable conditions Melanaphis pyraria may cause defoliation of cultivated pear trees, but more usually this species is not common enough to cause major damage. Basilova & Rakauskas (2012) found colonies of this newly invasive species were quite numerous in Druskininkai, but they were not as numerous as those of another invasive pear aphid, Dysaphis pyri, recorded in Lithuania from 1994 onwards.