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Myzodium [Macrosiphini]Myzodium apterae have a nodulose head, with well developed, rounded antennal tubercles and median frontal tubercles. Apterae are without secondary rhinaria on the antennae, but alatae have rhinaria scattered irregularly on antennal segments III, IV and commonly V. The apical rostral segment is 2.3-2.8 times its width at base. Tarsal chaetotaxy (=bristle arrangement) is 3-3-2 (fore-mid-hind). The abdomen has faint dorsal stripes. The siphunculi are subcylindrical, pigmented and usually coarsely imbricated, with the length 4.0-6.5 times the basal width. The cauda has a broad protruding base and a shield-shaped medially extended projection. There are 3 Myzodium species worldwide. The American species is now thought to host alternate from Crataegus to Mimulus, Veronica and various moss species, but other species in Europe & Asia are thought to be monoecious holocyclic or to exist as anholocyclic populations. Myzodium mimulicola (Orange-tinged monkeyflower aphid) Western NearcticAdult apterae of Myzodium mimulicola are brownish green, with some orange color laterally, and between the siphunculi. The siphunculi, cauda and legs are brown. The surface of the head is conspicuously nodulose, and both median frontal tubercle and antennal tubercles are well developed. The antennae are brownish, paler at the base of segment III, 0.60-0.95 times the body length, and with a terminal process 2.4-2.8 times the base of antennal segment VI. Segment III is without secondary rhinaria, and the hairs on that segment are very short and stout, <0.4 times the midpoint diameter. The rostrum reaches to or slightly beyond the metacoxae; the apical rostral segment is elongate, 2.2-3.5 times the basal width, with 2-4 accessory hairs. The thoracic and abdominal dorsum is reticulate, with no marginal tubercles. There are 3,3,2 hairs on the first tarsal segment. The abdomen is mainly membranous, without a large pigmented patch (cf. Myzodium modestum, which has a large pigmented patch on the abdominal dorsum). The siphunculi are strongly imbricated, gradually tapering from base to preapex, and with a marked flange; they are 2.7-3.0 times the cauda. The cauda has a broad basal part, and a distinctly narrower distal part, but its apex does not have a small, narrow digitate projection (cf. Myzodium modestum on mosses, which has such a projection on the caudal apex). The cauda has 4-6 hairs. The body length of adult apterae is 0.8-2.0 mm. Immatures are greenish or reddish.
Images above copyright Andrew Jensen, under a creative common licence. The alate Myzodium mimulicola has a blackish head & thorax, with the abdomen greenish-yellow suffused with red on the anterior part of the dorsum. The antennae are 0.78-0.86 times the body length, with secondary rhinaria distributed 21-32 on antennal segment III, 8-11 on segment IV, and 0-6 on segment V. The abdominal dorsum has a dark pigmented patch, or patch partially separating into transverse bars. Myzodium mimulicola was originally thought to be monoecious holocyclic on Mimulus guttatus, on angiosperms growing in wet situations such as Nasturtium & Veronica, and on certain mosses (Aulacomnium, Brachythecium, Calliergon, Philonotis, Saniona). Drews & Sampson (1937) found that they seem to prefer the lower and older leaves of Mimulus, and are not found on the tender growing tips. Pike et al. (2010) note it is occasionally abundant on Mimulus and Veronica, but always sparse on other hosts. However, recent work by Jensen reported in Aphidtrek indicates strongly that they are not monoecious as previously assumed, but heteroecious with Crataegus douglasii as the primary host. Sexuales have not yet been found. Myzodium mimulicola has a broad western Nearctic distribution, ranging from central California east to Utah, and north to southeastern Alaska, USA.
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