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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 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)

Both winged and wingless Illinoia lambersi exist as green, pink and yellow forms, which can occur in mixed populations. The images below show an adult Illinoia lambersiaptera and an alate of the green form. The apices of the antennal segments and the tips of the legs are dark. 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 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. This is in contrast to its close relative Illinoia azaleae (also found on Rhododendron) which has the second segment of the hind tarsus more than 1.5 times longer than that diameter. Other differences are that Illinoia azaleae is mainly found on azaleas and does not exhibit colour polymorphism (all are green).

 

The alate of Illinoia lambersi 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 rhododendron (Rhododendron), but have also been found on holly (Ilex aquifolium). 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.

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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 Illinoia liriodendri alate (second picture above) has a brown thorax, a greenish-yellow abdomen and black antennae and legs except for the bases of the femora.

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.

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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 (at least the fourth instars) are dusted with a fine wax powder (see second picture above).

 

The most distinctive feature of Illinoia morrisoni is the swollen siphunculi, which are not present on any other conifer-dwelling aphid.

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. Chaemocyparis, 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)

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Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure  provided by Blackman & Eastop (2006).

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References

  •  Heie, O.E. (1980-1995). The Aphidoidea, Hemiptera, of Fennoscandia and Denmark. (Fauna Entomologica Scandinavica) E.J. Brill, London