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Genus Melanaphis [Aphidini]
Melanaphis are small to medium-sized to elongate oval or pear-shaped aphids closely related to Rhopalosiphum aphids. Their siphunculi are shorter than the cauda. The abdomen has dark dorsal markings. The winged forms have dark forewing veins with the media vein twice-branched.
There are about 25 species of Melanaphis aphids. The three European species are associated with Pyrus (Rosaceae) and Poaceae, whilst the remaining East Asian species are associated with silvergrass (Miscanthus) or bamboo (Arundinaria).
Melanaphis donacis (Giant reed aphid)
Adult apterae of Melanaphis donacis are pear shaped. The dorsum is dark purplish-brown, but this colour is largely obscured by thick white wax in a characteristic pattern (see first picture below). Their antennae are 6-segmented with segments I to the basal parts of IV pale, and the remainder brown. The antennal terminal process is 1.1-1.9 times as long as the base of antennal segment VI (cf. Melanaphis elizabethae in more northern climes, which has the terminal process 2.5-3.1 times the base of that segment). The longest hairs on antennal segment III are 0.6-1.1 times the basal diameter of that segment (cf. Melanaphis elizabethae, which has the hairs on that segment 1.1.-1.5 times its basal diameter). The apical rostral segment (RIV+V) is 0.5-0.7 times length of the second hind tarsal segment (HT II) (cf. Melanaphis sacchari, which has RIV+V more than 0.8 times the length of HTII). The dorsal body hairs are short and inconspicuous (cf. Sipha maydis, which has long spine-like dorsal hairs). The siphunculi are dark, stump-shaped and broadest at the base. The dusky cauda has 12-22 hairs. The body length of adult Melanaphis donacis apterae is 1.5-2.2 mm.
Images above copyright Katja Schulz under a Creative Commons Attribution License.
Alatae of Melanaphis donacis have much less wax than the apterae, with secondary rhinaria distributed 3-13 on antennal segment III, 0-3 on segment IV and none on segment V. Immatures and recently moulted individuals also have less wax and are correspondingly more vulnerable to predators.
Melanaphis donacis is found on giant reed (Arundo donax) and common reed (Phragmites australis). Sexual forms have been found in southern France, with apterous males, but many populations worldwide are anholocyclic. The giant reed aphid is native to southern Europe, the Mediterranean region, north Africa, the Middle East, and Central Asia, eastward to India and Pakistan. It has been introduced to Argentina and Chile and apparently also to California.
Melanaphis pyraria (Pear-grass aphid)
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 (not pictured) 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 third picture above) are smaller, yellow-orange and live dispersed over the leaf blade.
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.
Melanaphis sacchari species group (Sugarcane aphid)
Melanaphis sacchari on sugarcane, and Melanaphis sorghi on sorghum have commonly been treated as synonyms, and referred to as the 'sugarcane aphid', despite evidence to the contrary. We first consider distinguishing members of the species group from other Melanaphis species. Adult apterae of Melanaphis sacchari sp. grp. (see first picture below) are broadly spindle-shaped. Their colour varies from pale yellow to yellow brown, dark brown, purple, or even pinkish, depending on host plant and environmental conditions. There is usually a variably developed black dorsal patch. Both the antennal and median frontal tubercles are weakly developed (cf. Melanaphis indosacchari, which has both the antennal and median frontal tubercles rather well developed). The antennal terminal process is 1.9-2.5 times the length of the cauda (cf. Melanaphis indosacchari, which has the terminal process 2.6-3.5 times the length of the cauda). The hairs on antennal segment III are very short being only 0.3-0.5 times the basal diameter of segment III. Abdominal tergites I-IV each have 1-2 hairs on each side and abdominal tergite VIII has 2 hairs. The longest hairs on the hind tibia are not more than 1.2 times the diameter of tibia at midlength. The siphunculi are dark, short and usually thick or rather thick, 0.70-1.05 times the length of the cauda, and usually with a well-developed, rather swollen flange. The cauda is dusky and short, less than 0.1 times the body length (cf. Sitobion miscanthi & Hysteroneura setariae, both of which have a fairly long pale cauda, greater than 0.14 times the body length). The body length of adult apterae is 1.1-2.0 mm.
The two members of the Melanaphis sacchari species group can be distinguished thus:
First image above by permission, copyright Sunil Joshi & Poorani, J., Aphids of Karnataka
The alate (see second picture above) has several dark sclerotic cross bars on the dorsum, and the antennae have 4-16 secondary rhinaria on segment III, 0 - (rarely)6 on segment IV and none on segment V.
Both Melanaphis sacchari and Melanaphis sorghi live in ant-attended colonies on cereals and grasses (Poaceae). Melanaphis sacchari is found especially on sugar (Saccharum), but also on cereals such as rice (Oryza) and sorghum (Sorghum) and some Araceae. Melanaphis sorghi is mainly found on sorghum, but is also found on other grasses and cereals. In most places populations are anholocyclic, but in China Melanaphis sacchari sp. grp. is monoecious holocyclic (with alate males) with Miscanthus sacchariflorus (Poaceae) as the overwintering host. Nibouche et al., 2021 found both members of the species group distributed throughout the tropical and subtropical regions. So far Melanaphis sorghi is the sole detected of these in West and in Southern Africa. In East Africa, Melanaphis sacchari has been detected in Kenya and Tanzania, and Melanaphis sorghi in Uganda and Kenya. The islands of Reunion and Mauritius in the Indian Ocean are exclusively colonized by Melanaphis sacchari. The Nearctic zone is colonized by both species, as a result of the recent introduction of Melanaphis sorghi in the Americas. In the Neotropical zone, Melanaphis sacchari was the only species observed before 2016, but studies indicate that Melanaphis sorghi is now present in Brazil. In Asia, Melanaphis sorghi is present in China and India, and Melanaphis sacchari in Cambodia. In Australia and in Hawaii, only Melanaphis sacchari has been detected.