Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
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 (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. They can be seen clearly in the alcohol-preserved specimens 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. 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)
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 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 ).
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.