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Coloradoa are small green or reddish globose (globe-shaped) aphids. They have a very convex frons with no antennal tubercles. Their antennae are always shorter than the body, and the terminal process is always longer than the base of the last antennal segment. The dorsal body hairs are short or very short and are expanded at the tip. The apical rostral segment is acutely pointed with concave sides. The siphunculi vary in size and shape.
Coloradoa achilleae (Small yarrow aphid) Europe, Asia, North America
Adult viviparous apterae of Coloradoa achilleae are small oval aphids, coloured pale green to greyish green or reddish (see pictures below). The tips of the antennae and the tarsi are dark. The antennal terminal process is 1.1-1.4 times longer than the base of the sixth abdominal segment. The siphunculi are 1.3-1.8 times the length of the cauda. The siphunculi are near cylindrical, or with a weakly swollen apical part, and a well developed flange. The cauda is obtuse (=not pointed), slightly constricted at the base and with 5 hairs.
Coloradoa achilleae is a small, inconspicuous species that can be found feeding on yarrow (Achillea millefolium) especially on leaves at the base of the stem. Their overwintering eggs hatch in late spring, but there is no information available on the population trends of this species through the year. Sexual forms develop in autumn, with eggs laid at the base of the host plant. The small yarrow aphid is found in Britain, and throughout Europe into Russia, as well as having been introduced into USA.
Coloradoa bournieri (Cotton lavender aphid) Middle East, Western and Southern Europe
Adult apterae of Coloradoa bournieri (see first picture below) are pale or dirty green with dark apices to the appendages. The terminal process of the sixth antennal segment is quite short being 1.2-1.5 times the length of the base of that segment. The fused last two rostral segments (RIV+V) are 1.2 to 1.5 times longer than the second segment of the hind tarsus (HTII) (cf. Coloradoa absinthii, which has the fused last two rostral segments shorter than the second segment of the hind tarsus). Their siphunculi are clearly swollen and curved outwards towards apices, with the swelling asymmetrical and greatest on inner side (see micrograph below) (cf. most other Coloradoa species where siphunculi are cylindrical or only weakly and symmetrically swollen. The body length of Coloradoa bournieri aptera is 1.1-1.5 mm.
Coloradoa bournieri feeds on cotton lavender (Santolina chamaecyparissus) and green cotton lavender (Santolina viridis). No sexual forms are known and the species breeds parthenogenetically through the year. The cotton lavender aphid is indigenous to Mediterranean Europe and the Middle East where its host plant occurs naturally. It has now been found in Britain, and Argentina (coll. Durante, 2009).
Coloradoa rufomaculata (Green chrysanthemum aphid) Central & East Asia, Europe, North America, Australia
Coloradoa rufomaculata (see first two pictures below) are very small aphids found on cultivated chrysanthemum. Adult apterae have large bright red eyes and a green dorsum, marked with a few yellow and red spots of internal colour. The antennae are 0.5-0.7 times as long as body, with the terminal process 1.5-2.0 times as long as base of last antennal segment; antennal segments V & VI are dark brown. Antennal hairs are very short, about 0.25 times the basal diameter of segment III. The triommatidia is merged with the compound eye, so there is no distinct ocular tubercle. The apical rostral segment (RIV+V) is slender and pointed with six short secondary hairs, and is about 1.2 times the length of the second hind tarsal segment (HTII); (cf. Coloradoa tanacetina, which has RIV+V less than 1.1 times HTII). The dorsum bears numerous fan-shaped hairs (cf. Coloradoa tanacetina, which has very small dorsal hairs weakly club-shaped, or with only slightly expanded apices). The siphunculi vary in pigmentation from dusky just at the apex to almost wholly dark; they are symmetrically swollen just before apex, and are 0.17-0.20 times the body length (cf. Coloradoa tanacetina, which has siphunculi 0.13-0.18 times the body length). The siphunculi are almost smooth on the basal part, compared to the coarsely imbricated distal part (cf. Coloradoa artemisiae, which has siphunculi that are coarsely imbricated on both the basal and distal parts. The cauda is pale or dusky, oblong, triangular, not constricted, with 4-5 hairs. The body length of adult Coloradoa rufomaculata apterae is 0.9-1.5 mm.
Images above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka (accessed 12/2/20).
The alate Coloradoa rufomaculata (not pictured) is green with pale marginal and intersegmental sclerites. The antennae and tips of legs are black, and the siphunculi and cauda are dark. The antennae have 6-10 secondary rhinaria on segment III, 6-10 on IV and 0-3 on V.
Coloradoa rufomaculata is monoecious on chrysanthemum and Artemisia species, especially florists chrysanthemum (nominally Dendranthema × grandiflorum) and Indian chrysanthemum (Chrysanthemum indicum). The aphid has the peculiar habit of settling in the notches of the serrated leaves of the host plant. In India it is often found in association with Aphis gossypii and Macrosiphoniella sanborni. Oviparae and males have been reported from Australia, but most populations are anholocyclic. Coloradoa rufomaculata has a cosmopolitan distribution including North America, Europe, central and east Asia and Australia, but is mainly found in glasshouses in cold temperate climates.
Coloradoa tanacetina (Tansy leaf-margin aphid) Northern Europe, North America
Adult apterae of Coloradoa tanacetina are yellowish green or greenish yellow-brown, with the tips of the antennae and tarsi dark. The antennal terminal process is 1.4-2.0 times longer than the base of antennal segment 6. The last two fused segments of the rostrum (RIV+V) are 0.9-1.0 times longer than the second hind tarsal segment The longest hairs on abdominal tergite 8 are only 14-24 μm. The siphunculi are cylindrical and 1.3-2.2 times longer than the cauda. The length of the adult aptera of Coloradoa tanacetina is 1.1-2.0 mm.
Winged forms (not shown) have 9-15 secondary rhinaria on antennal segment 3, 5-11 on segment 4 and 1-9 on segment 5.
Coloradoa tanacetina feed in the indentations at the leaf margins of tansy (Tanacetum vulgare). Sexual forms of the aphid (pale green oviparae and very small orange-yellow males) occur in September and October. Coloradoa tanacetina are found across northern Europe, and have been introduced to USA.