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Genus Illinoia [Macrosiphini]
Illinoia are medium to rather large usually greenish aphids with long siphunculi. The antennal tubercles are well developed, with their inner faces divergent. The median tubercle is frequently also well developed. The siphunculi are weakly to moderately swollen, similar to those of Amphorophora, but with a few rows of rather large polygonal cells occupying the distal 0.06-0.2 of total length. The cauda is shorter than siphunculus, slender and finger shaped.
There are about 45 mostly North American Illinoia species, although some have been introduced to other parts of the world including Europe. Most species retain a sexual stage in the life cycle. There is no host alternation and many species in the two main subgenera are associated with the Heath and Rhododendron family (Ericaceae). Other species feed on taxonomically diverse plants. They are not attended by ants. Some species are important pests of ericaceous plants.
Illinoia lambersi (Rhododendron aphid)
Winged and wingless Illinoia lambersi both exist as green, pink and yellow forms (see first picture below of yellow aptera) which can occur in mixed populations (cf. Illinoia azaleae which is always green). The apices of the antennal segments and the tips of the legs are dark. The second segment of the hind tarsus is rather short and less than 1.5 times longer than maximum diameter of the swollen part of the siphunculi (cf. Illinoia azaleae which has the second segment of the hind tarsus more than 1.5 times longer than that diameter). The siphunculi are mostly pale but with darkened apices. They are slightly swollen, strongly attenuated near the tip, and 2.0-2.5 times longer than the cauda. The cauda is mainly pale but dusky towards the tip. The body length of Illinoia lambersi apterae is 2.2-3.3 mm.
The alate of Illinoia lambersi (see second picture above of green alate) has rather indistinct abdominal marginal and intersegmental pleural sclerites. The antennae are only slightly longer than the body and have 21-30 secondary rhinaria placed along the whole segment, not precisely in a row (cf the antennae of Illinoia azaleae which have 7-21 secondary rhinaria in a row).
Colonies of Illinoia lambersi are mainly found on the new shoots and flower buds of rhododendrons and azaleas (Rhododendron), but have also been found on holly (Ilex aquifolium) (cf. Illinoia azaleae which mainly occurs on azaleas). Illinoia lambersi is indigenous to North America where it is widely distributed and sexual forms occur. It is now also well established on rhododendron in South America (Chile), Japan and parts of Europe including Denmark, England and the Netherlands where it overwinters as viviparae.
Illinoia liriodendri (Tulip-tree aphid)
Illinoia liriodendri apterae are spindle shaped and pale green, lightly dusted with wax (see first picture below). There are also yellowish and pink-red forms. The antennae are black except at the bases, and are 1.2-1.6 times as long as the body. The legs are pale green except for black apices to the tibiae and tarsi. The siphunculi are black except at the base, and are 2.3-2.9 times as long as the cauda. They are slightly swollen on the distal half, sometimes bent outwards, and with reticulation on the apical one-tenth to one-eighth. The cauda is pale greenish-yellow and is elongate. The body length of an adult Illinoia liriodendri aptera is 1.7-2.5 mm.
The tulip-tree aphid feeds on undersides of the leaves of tulip tree (Liriodendron tulipifera). Dense populations can build up resulting in large deposits of honeydew on the leaves. Sexual forms occur in autumn. Illinoia liriodendri is native to North America, but in 1998 was found in France. It has since been reported in other European countries and in Japan.
Illinoia morrisoni (Sequoia aphid)
Adult apterae of Illinoia morrisoni (see first picture below) are spindle-shaped and rather dark apple green in colour. The antennal terminal process is 3.6-4.7 times the length of the base of the sixth antennal segment. The first tarsal segments usually have 3 hairs, all subapical, and the apices of the legs are dark. The siphunculi are distinctly swollen and darkened at the tips. The adult apterae are rather small with a body length of 1.5-2.3 mm. Immature Illinoia morrisoni are dusted with a fine wax powder (see second picture below).
Illinoia morrisoni feeds on the terminal leaves and shoots of many species of conifer, mainly in the Taxodiaceae (e.g. Sequoia, Taxodium) and Cupressaceae (e.g. Chamaecyparis, Cupressus, Juniperus, Thuja). Sexual forms have not been described, and it appears to overwinter as parthenogenetic forms. The sequoia aphid is indigenous to western North America, but has now been recorded from Central and South America and several parts of Europe (Britain, France, Italy and Portugal).
Illinoia rubicola (Spot-winged raspberry aphid)
Adult apterae of Illinoia rubicola are pale greenish-yellow, usually with a broad dark green spinal stripe and dark green abdominal margins. The antennal terminal process is 5.5-8.2 times as long as the base of antennal segment VI (cf. Illinoia maxima, which has the terminal process 4.5-6.2 times the base of segment VI). The third antennal segment bears 7-22 secondary rhinaria (cf. Illinoia davidsoni in which antennal segment III bears 20-23 secondary rhinaria). The apical rostral segment (RIV+V) is 1.4-1.85 times as long as the second hind tarsal segment (HTII) (cf. Illinoia davidsoni, which has RIV+V 1.9-2.2 times the length of HTII). There are well developed marginal tubercles present on all of abdominal tergites I-VII, and spinal tubercles usually on tergites VII-VIII (cf. Illinoia maxima, which usually has marginal tubercles only on tergites II-V, and no spinal tubercles). The siphunculi are light brown with darker tips and a sub-apical zone of polygonal reticulation distal to a swollen part (cf. various Macrosiphum and Sitobion species, which have their siphunculi tapering or cylindrical). The body length of adult Illinoia rubicola apterae is 3.1-4.6 mm.
Images above by permission, copyright Claude Pilon, all rights reserved.
Alatae of Illinoia rubicola (see second picture above) have a dark pterostigma and a large black spot at the tip of each forewing (cf. the alate Illinoia davidsoni, which has no black spot at the tip of each forewing). Immatures (see left-most aphid in picture below) have somewhat shorter and less swollen siphunculi, but otherwise resemble the adult apterae.
The spot-winged raspberry aphid can be found on stems of American red raspberry (Rubus strigosus, and on a few other closely-related Rubus spp. Illinoia rubicola is reported as markedly gregarious, and strong colonies are often found on the undersides of the leaves and on the canes near the tip of new growth. It does not host alternate and produces oviparae and alate males in October, overwintering as eggs on raspberry. It is a vector of black raspberry necrosis virus (BRNV), but not of raspberry leaf curl. BRNV causes mild leaf mottle. Illinoia rubicola is widely distributed in the United States and Canada.
Illinoia spiraecola (Varicoloured spirea aphid)
Apterae of Illinoia spiraecola are various hues of red, green and yellow (see first picture below of immature green aptera), often with a darker spinal stripe. The longest hairs on antennal segment III of the adult aptera are 0.30-0.45 times the basal diameter of that segment (cf. Illinoia spiraeae and Illinoia macgillivrayae, which have the longest hairs on antennal segment III 0.20-0.25 times the basal diameter). Antennal segment V is 1.8-2.4 times the length of the cauda (cf. Illinoia spiraeae and Illinoia macgillivrayae which have antennal segment V 1.2-1.8 times the caudal length). The femora and tibiae are light brown and the tarsi black. The first tarsal segments have 3 hairs (cf. Illinoia spiraeae and Illinoia macgillivrayae which have 4-5 hairs on the first tarsal segments). The siphunculi are light brown with a dark tip; they have subapical reticulation with several rows of closed polygonal cells, and are slightly swollen to 1.2 to 1.5 times their basal diameter on the distal third. The body length of adult Illinoia spiraecola apterae is 2.5-3.2 mm.
Note: The other Illinoia species that have been found on Spiraea species (namely Illinoia spiraeae and Illinoia macgillivrayae) only occur in the west of the USA and Canada.
Images above by permission, copyright Claude Pilon, all rights reserved.
Alatae and immature Illinoia spiraecola (see pictures above) are similarly coloured to the adult apterae. Most of our images show the green form, but some of the young nymphs in the picture below are of the yellow form.
Illinoia spiraecola feeds on a variety of meadowsweets (Spiraea spp.). There is no host alternation, and it is assumed that sexual forms develop in autumn. In Maine several colour varieties of the species have been found on Spiraea x vanhouttei, namely vermillion (scarlet), rose pink, bright green, yellow green, and lemon yellow. It is widely distributed in North America.