Last year, 2007, the silk-button and spangle galls on the leaves of oak trees in my garden were joined by large numbers of a new gall. It appeared as a raised dome about 3 mm in diameter on the upper surface and the corresponding depression on the lower surface was covered by what looked like an intricate miniature manhole cover. This was the nymph of the Trioza remota, a member of Sternorrhyncha, one of stranger suborders of the hemiptera
    (Hemiptera > Sternorrhyncha > Psylloidea > Triozidae > Trioza remota);
which also contains the Coccoidea, the scale insects, with their weird morphology and life cycles (Kirby et al. 2007, White Admiral 67). Unlike the scale insects, Trioza has legs terminating in two claws, which anchor it firmly in its cavity while it inserts its feeding tube into a phloem vessel. The almost circular outline of the nymph is produced by the growth of the fore and hind wing pads.

A search of the Web led to a University of British Columbia Botanical Garden site which, in addition to information about psyllid morphology, has a link to a site about psyllid acoustics with recording of the squeaks produced by some Australian psyllids. This, plus the vernacular name, ‘jumping plant lice’, raised the possibility of finding a jumping, squeaking adult Trioza.

At the end of October I saw the first of what I thought was a Trioza imago; to be sure I sent a photograph to Jerry Bowden, the SNS gall recorder. His opinion, based on the wing patterns, was that it was not Trioza, but might actually be a Psocopteran (psocids, barkflies and booklice) and pointed to a barkfly recording website. Closer inspection of pattern of wing venation of the flies confirmed his identification, although I was not too ashamed as both Dolling (1991) and Chinery (1973) comment on the similarity of imagos of the psyllids and the psocids.

Psocids are small insects 4 mm long, including the wings, when mature. The long-legged, active nymphs go through six instars, each instar increasing in size and wing development. They feed mostly on organic matter such as lichens, algae, fungi and fungal spores, and dead plant and insect material.

The identification of the barkflies clarified the identity of small patches of web enclosing sausage shaped eggs between diverging veins on the leaf lower surface and the active nymphs frequently seen scurrying about the leaves.

As the season progressed and the oaks shed twigs with attached dead leaves, it was easy to collect large numbers of barkflies simply by shaking the twigs into a tray. Among the insects collected there was variation of size and pigmentation indicating that there were several species present. A sample sent to Bob Saville, the National Barkfly Recording Scheme organiser, contained four species, one of which (Trichopsocus clarus) is rare in Britain and merits inclusion in the Entomologists’ Record.

[The barkflies recording scheme was started in 2006 with the primary aim of building up as full a picture as possible of the distribution of the species in Britain and Ireland. Knowledge of distribution is necessary to determine their national and local statuses and, in particular, whether any are under sufficient threat to require conservation action.]

Records show an almost complete absence of barkflies in East Anglia, but with such a small insignificant insect there is always a suspicion that they have been overlooked, although I, for one, have systematically looked at my trees for the past 10 years or so (Kirby, 2004, White Admiral 58).

The appearance of such large numbers of barkflies where none has been seen before may be attributed to climate change. There may also have been local factors at work. As well as the many phloem feeding Trioza nymphs, 2007 was notable for big infestations of oak aphids and the leaves became covered with sticky honeydew, often colonised by an unidentified white, fluffy fungus. This may have attracted barkfly nymphs and imagos which were seen around the fungus and provided food for the big population increase.

Barkfly eggs in the bifurcation of a leaf vein. They were originally covered in a fine web which has been pulled aside.
Trioza remota nymph anchored over a depression in the leaf. The abdomen is at the top of the picture and two lateral lighter coloured bulges are the wing pads.
Barkfly nymph with developing wings.
Barkfly imago
Fore wing of a barkfly. The veins of the wing of a psyllid are fused basally so that they appear to come from one central stalk

Fig 1: Current distribution of Psocoptera records from the National Biodiversity Network Gateway. (July 2007). Reproduced with permission.

References Chinery, M (1973) Insects of Britain. Collins, London. Dolling, W.R. (1991) The Hemiptera. OUP.