Illinoia morrisoni

Identification & Distribution:

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).

Micrographs of clarified mounts by permission of Roger Blackman, copyright AWP all rights reserved.

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)

Biology & Ecology:

Illinoia morrisoni is an American species which was first found in Europe by Dr V. Eastop on Sequoia sempervirens in Kew Gardens, Surrey in September 1960 (Stroyan, 1964). Rabasse et al. (2005) recorded the species in France on Cupressus arizonica, Coceano & Petrovic-Obradovic (2006) recorded alatae in suction trap catches in Italy and Rodrigues et al. (2006) caught alatae in a suction trap in Portugal.

In Britain, since Eastop's original find, it has occurred in suction-trap catches in Scotland since 2001 (Blackman (2010)). In September 2007 Baker (2009) found the species on a young Sequoia sempervirens at Roath Park, Cardiff, Wales. Then in September 2014 we found Illinoia morrisoni using a beating tray on a large Sequoia sempervirens at Bedgebury Pinetum in Kent.

We tend not to use a beating tray much because this sampling method (sometimes poetically called 'thrashing') does tend to damage aphids. We concentrate on photographing the aphids in situ, along with their parasitoids and predators.

However, cryptic species like the sequoia aphid are very hard to spot on their foodplant, so beating is sometimes the best way to check if there are any interesting aphids around. The aphid above is a fine adult Illinoia morrisoni that dropped on to the tray after about the third 'thrash'.

We have since found a flourishing colony of this aphid (see picture below) on another conifer species at Bedgebury Pinetum, the Bermuda juniper (Juniperus bermudiana).

We suspect this aphid is now common and widely distributed in Britain given it is known to be present in south-east England, Wales and Scotland (albeit the latter only via suction traps).

Other aphids on same host:

Taxodiaceae

• Illinoia morrisoni has been recorded from 1 Sequoia species (Sequoia sempervirens).

  Blackman & Eastop list 2 species of aphid as feeding on redwood conifers (Sequoia species) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists both as occurring in Britain (Show British list).

• Blackman & Eastop list 2 species of aphid as feeding on 1 Taxodium species (Taxodium distichum) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists one as occurring in Britain. (Show British list).

Cupressaceae

• Illinoia morrisoni has been recorded from 1 Chamaecyparis species (Chamaecyparis lawsoniana).

  Blackman & Eastop list 6 species of aphid as feeding on cypress or false cypress (Chamaecyparis species) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 4 as occurring in Britain (Show British list).

• Illinoia morrisoni has been recorded from 6 Cupressus species (Cupressus arizonica, Cupressus funebris, Cupressus lusitanica, Cupressus macrocarpa, Cupressus sempervirens, Cupressus torulosa).

  Blackman & Eastop list 8 species of aphid as feeding on cypresses (Cupressus species) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 5 as occurring in Britain (Show British list).

• Illinoia morrisoni has been recorded from 12 Juniperus species.

  Blackman & Eastop list 21 species of aphid as feeding on junipers (Juniperus species) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 8 as occurring in Britain (Show British list).

• Illinoia morrisoni has been recorded from 1 Thuja species (Thuja plicata).

  Blackman & Eastop list 4 species of aphid as feeding on Thuja species worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 3 as occurring in Britain (Show British list).

Damage and control

There are no records of this aphid causing damage to conifer trees, neither in its native North America nor in countries it has established itself in.

Acknowledgements We especially thank the UK Forestry Commission Bedgebury Pinetum for their kind assistance, and permission to sample. Our particular thanks to Roger Blackman for images of his clarified slide mounts. Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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).

Useful weblinks

References  Baker, E.A. (2009). Observations of aphids (Aphidoidea) new to Wales. British Journal of Entomology and Natural History 22, 235-246. Abstract  Coceano, P.G. & Petrovic-Obradovic, O. (2006). New aphid species for Italy caught by suction trap. Phytoparasitica 34(1), 63-67.  Rabasse, J.M. et al. (2005). On the presence in Europe of two Illinoia aphids of North American origin (Homoptera, Aphididae). Bolletino di Zoologia Agraria e di Bachicoltura 37(3), 151-168. Abstract  Rodrigues et al. (2006). Interactions between ground cover management, hedges and aphids in lemon orchards. Bulletin OILB/SROP 29(3), 117-125  Abstract  Stroyan, H.L.G. (1964). Notes on hitherto unrecorded or overlooked British aphid species. Transactions of the Royal Entomological Society of London 116(3), 29-72. Abstract