Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Cherry - grass aphidsOn this page: enigmae maidis nymphaeae oxyacanthae padi rufiabdominale Rhopalosiphum
Genus Rhopalosiphum [Aphidini]
Rhopalosiphum are small to medium-sized aphids with a body that is broadly oval to rather elongate in shape. The dorsal body cuticle is membranous with pigmented patterns confined to small intersegmental muscle sclerites and variably present bands across the pronotum and abdominal tergite 8. Marginal tubercles are normally present on the pronotum and on abdominal segments 1 and 7. The siphunculi are variable in shape - cylindrical, tapering, vasiform or slightly swollen, always with an apical expansion and a strong flange. The cauda is shorter than the siphunculi and bluntly tapering or tongue shaped.
There are about 14 species in the Rhopalosiphum genus. Most species are holocyclic over some part of their distribution, but many have anholocyclic populations. Rhopalosiphum species usually host alternate between plum (Prunus spp.) or apple (Pyroideae) as primary hosts and grasses (Poaceae) or sedges (Cyperaceae) as secondary hosts. Rhopalosiphum species may be ant attended and some are important crop pests.
Rhopalosiphum enigmae (American cattail aphid)
Adult apterae of Rhopalosiphum enigmae are broadly oval and coloured dark reddish brown to greenish brown or dark green (see first picture below). They usually have a quite marked red-brown patch between and anterior to the siphunculi (most evident in immatures) similar to that found in Rhopalosiphum padi. The terminal process is 4.0-6.3 times as long as the base of antennal segment VI (cf. Rhopalopsiphum maidis, which has the terminal process 1.7-2.8 times the base of segment VI). The longest hairs on antennal segment III are 0.8-2.0 times the basal diameter of that segment. The dorsal abdominal cuticle has a pattern of blunt spicules arranged in polygons. Small marginal tubercles are usually present on some or all of abdominal tergites II-VI as well as I and VII (cf. Rhopalosiphum padi, which has no marginal tubercles on tergites II-VI). Their femora are dark brown, paler at the base. The siphunculi appear more or less cylindrical or slightly swollen, narrowing sharply just before a large flange (cf. Rhopalosiphum nymphaeae, which has slightly swollen siphunculi with a narrower section on the basal half; and cf. Rhopalosiphum maidis, which has siphunculi with no subapical constriction and a small flange). The siphunculi are 0.12-0.17 times the body length, and more than 2.1 times the length of the cauda (cf. Rhopalosiphum padi, which has siphunculi less than 2.2 times the length of the cauda). The body length of adult Rhopalosiphum enigmae apterae is 1.7-2.3 mm.
Both images above by permission, copyright Claude Pilon, all rights reserved.
Rhopalosiphum enigmae alatae (not pictured) have 7-15 secondary rhinaria an antennal segment III, and 0-3 on segment IV. Young immatures (see second picture above) are light greenish yellow to umber (greyish-brown to dark reddish-brown).
Rhopalosiphum enigmae feed on cattails (Typha spp.), especially Typha latifolia, forming colonies concealed within leaf sheaths. The species is also recorded from a bur reed (Sparganium sp.). There is no host alternation and sexual forms develop in autumn. The American cattail aphid is widely distributed in North America.
Rhopalosiphum maidis (Corn leaf aphid)
Adult apterae of Rhopalosiphum maidis (see first picture below) are elongate-bodied olive green to bluish-black aphids, sometimes dusted with wax. The areas around the bases of the siphunculi and often other parts of the dorsum are a darker green or purplish black (cf. Rhopalosiphum padi which has a rusty red suffusion around the siphuncular bases). The antennae are dark except for segment III and part of IV, and the terminal process is 1.7-2.8 times the length of the base of antennal segment VI. The apical segment of the rostrum (RIV+V) is about 0.8 times the length of the second hind tarsal segment (HTII). The siphunculi are dark and rather short, not flared at the apex and only 1.1-1.4 times the length of the cauda. Immature Rhopalosiphum maidis are usually a somewhat lighter blue-green, with clearly marked darker areas around the bases of the siphunculi.
All images above copyright Mihajlo Tomić, all rights reserved.
The alate Rhopalosiphum maidis (see second picture above) has a yellow-green to dark green abdomen with darker areas around the bases of the siphunculi, but no other dorsal dark markings anterior to the siphunculi.
Rhopalosiphum maidis populations are anholocyclic on grasses (Poaceae) in most parts of the world, but in parts of Asia (where Rhopalosiphum maidis originated) it host alternates with Prunus spp. as the primary host. It only occurs sporadically in cool temperate climates such as Britain and southern Scandinavia, but is cosmopolitan in warmer climates, where it can be an important pest of cereals. Rhopalosiphum maidis are commonly attended by ants which consume the abundant honeydew.
Rhopalosiphum nymphaeae (Water lily aphid)
Apterae of Rhopalosiphum nymphaeae are brownish on the primary host (plum), and more or less shiny reddish-brown to dark olive (see first picture below) on the secondary host (water lily). The dorsal cuticle has reticulation formed by regularly shaped roundish bead-like spinules. The antennae are about 0.6 times the body length. The terminal process of antennal segment VI is about 3-4 times the length of the base of that segment. On the primary host the apical rostral segment (RIV+V) is 1.0-1.1 times longer than the second hind tarsal segment (HTII). On the secondary host RIV+V is 1.15-1.45 times longer than HTII. The siphunculi are more than twice the length of the cauda and are swollen on the distal half. The cauda is elongate and slender. The body length of Rhopalosiphum nymphaeae aptera is 1.6-2.6 mm.
Rhopalosiphum nymphaeae alatae (see second picture above) are shining brown, sometimes with white dorsal wax markings. The immatures (and sometimes the adults) may be dusted with a light grey wax on the head, thorax and legs.
In spring the water lily aphid feeds on various Prunus species (such as Prunus spinosa) where it feeds on leaf petioles and fruit stalks curling the leaves. In early summer Rhopalosiphum nymphaeae alatae migrate to the secondary hosts comprising a large variety of water plants, including Nymphaea (water lilies), Potamogeton (pondweeds), and Sparganium (arrowheads). Its distribution is almost cosmopolitan - in Britain it is found from the south of England to the north of Scotland.
Rhopalosiphum oxyacanthae (= insertum) (Apple-grass aphid)
Rhopalosiphum oxyacanthae apterae (see first picture below) on apple are small light green to yellow-green aphids that are elongate-oval in shape. They have fairly well-marked dark green stripes down the centre of the back with cross bars and along each side. The 5-segmented antennae are about a third the length of the body. The frontal head tubercles are low, with the median frontal tubercle about the same height as the antennal tubercles. The siphunculi are quite short - about one tenth as long as the body - slightly swollen subapically, and pale with dusky tips. The body length of the adult aptera on the primary host is 2.1-2.6 mm.
Winged Rhopalosiphum oxyacanthae viviparae (see second picture above) have a blackish head, thorax and siphunculi and a green abdomen with some brown plates and pigmentation. The apple-grass aphid aptera on its secondary host - grass roots - (see first picture below) is pale green, yellowish green or bluish green with no clear markings. The antennae are normally 5-segmented and much shorter than half the body length. The siphunculi are brown, 0.11-0.13 times the body length and nearly twice the length of the cauda. The body length of the apterous adult on the secondary host is 1.1-1.9 mm.
The apple-grass aphid host alternates between apple and related species (Rosaceae: Cotoneaster, Crataegus, Malus, Pyrus, Sorbus) and the roots of various grasses (Poaceae). It has a sexual stage in its life cycle with eggs laid on apple. The first generation in March induces curling perpendicular to the mid-rib of the young leaves of the primary host. Apple-grass aphids may be attended by ants. Winged forms migrate in late May-June to the underground parts of various grasses, but colonies may persist into summer on primary hosts. Rhopalosiphum oxyacanthae is found in Europe and Japan.
Rhopalosiphum padi (Bird cherry - oat aphid)
On the primary host (bird cherry) feeding by the fundatrix of Rhopalosiphum padi & her offspring induces a rolled leaf gall (see first picture below). Apterae in the gall have a coating of mealy wax (see second picture below). Apterae on the secondary host (grasses) (see third picture below) are pale green to dark green, brown or nearly black, with a rust-red suffusion around the base of each siphunculus. The terminal process of the sixth antennal segment of the aptera is 3.1-5.2 times as long as the base of that segment. The apical ends of the siphunculi are slightly swollen and end with a strong flange preceded by a distinct constriction. The cauda is rather pale and shorter than the siphunculi. The body length of Rhopalosiphum padi apterae is 1.2-2.4 mm.
The alate vivipara of Rhopalosiphum padi is green, with a rusty red suffusion around the siphuncular bases. It has marginal tubercles on most or all of abdominal segments I to VII. The apical rostral segment (RIV+V) is 0.75-0.95 times as long as the second hind tarsal segment (HTII). The longest hairs on antennal segment III are 0.53-0.76 times the basal diameter of that segment.
The bird cherry - oat aphid host alternates between bird cherry (Prunus padus) as the primary host and various grasses (Poaceae) as the secondary host. Some populations reproduce parthenogenetically all year on grasses. Rhopalosiphum padi is the principal vector of barley yellow dwarf virus, and has a cosmopolitan distribution.
Rhopalosiphum rufiabdominale (Rice root aphid)
Adult apterae of Rhopalosiphum rufiabdominale on the primary host (not pictured) are reddish-brown or greenish-brown with bluish-white mealy wax on the sides of the body and forming dorsal cross-bands. Apterae on the secondary host are dark green or brownish with a rusty-red suffusion about the bases of the siphunculi (see pictures below - note they are of immatures). The hairs on antennal segment III are markedly longer than the basal diameter of that segment; on the secondary host the longest hairs are 3-5 times the basal diameter (cf. Rhopalosiphum nymphaeae and Rhopalosiphum padi, which has the hairs on antennal segment III shorter than or equal to the basal diameter of that segment). Marginal tubercles are usually only present on abdominal tergites I and VII (cf. Rhopalosiphum nymphaeae, which has marginal tubercles on tergites I-VII). The siphunculi are less than 0.3 mm long, or 1.7-1.8 times longer than the cauda, and with no discernible subapical swelling (cf. Rhopalosiphum nymphaeae, which has siphunculi more than 0.3 mm long and swollen proximal to the subapical constriction). The body length of adult Rhopalosiphum rufiabdominale apterae is 2.0-2.6 mm.
First image above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka (accessed 12/2/20).
Alatae on the secondary host are dark green with a rusty suffusion around the bases of the siphunculi. They usually have 5-segmented antennae with 3-35 secondary rhinaria on antennal segment III, and 0-4 on segment IV.
Rhopalosiphum rufiabdominale is native to east Asia where it host alternates from Prunus species, including Japanese apricot (Prunus mume) and Chinese plum (Prunus salicina), to the roots of various grasses (Poaceae), sedges (Cyperaceae), potatoes / nightshades (Solanaceae), and cannabis (Cannabaceae). It has also been found overwintering in Europe on domestic plum (Prunus domestica) and apricot (Prunus armeniaca). Rhopalosiphum rufiabdominale is found in warmer climates, or glasshouses, in much of the rest of the world as anholocyclic populations on the secondary hosts. It is a major pest of rice in east Asia and of cannabis in hydroponic cultivation.