Notes on the New Zealand Wood-wasp Ophrynopus schauinslandi Ashmead.
[Read before the New Zealand Institute Science Congress, Dunedin, 30th January, 1926; received by Editor, 5th March, 1926; issued separately, 19th February, 1927.]
(Communicated by Dr. R. J. Tillyard, F.R.S.)
While collecting at Third House near the Dun Mountain tramline, the author had the good fortune to come unexpectedly on a breeding ground of Ophrynopus schauinslandi.
It is situated at an elevation of about 2,000 ft., amongst dense native bush, which was burnt in 1918. Many dead trees are still standing, and having been killed mainly by heat, remain uncharred and consequently open to attack by insects. Weathering has deprived most of them of bark, and already many have succumbed to the attacks of native wood-borers, and have fallen.
From the tramway the crown of a ridge extending through this area is comparatively clear of vegetation for two hundred yards, and it is possible to work down into the standing trees for a short distance on each side. The remainder of the area is practically in accessible to the collector, being a mass of intermingled, fallen tree trunks and loose vegetation often over six feet in height. The ridge is exposed, and receives the full benefit of the sun's rays through greater part of the day, a condition well suited to the habits of Ophrynopus.
Previous to 1924 little was known about this insect; apart from the originally described specimen from the Chatham Islands, only four were known to the author, all of these now being in his own collection. One was forwarded by Mr. T. R. Harris from Ohakune in the North Island; another sent was secured by Mr. J. W. Campbell of Christchurch, at Blackball, Westland, and the two remaining specimens were taken by the writer on the Port Hills, Christchurch.
Unfortunately I have been unable to secure Ashmead's description of Ophrynopus schauinslandi and do not know the sex of his type, but the sexes are very much alike except for the well-known differences in the antennae and fore-tibiae.
Generally the fauna of the Chatham Islands may be considered to parallel that of the mainland, and it is on that supposition that the mainland species has been so determined.
Ophrynopus schauinslandi varies greatly in size, ranging from 6 mm. to 10 mm. in length, is strongly built, but is exceedingly active. By approaching standing dead trees well exposed to the heat and light of the sun, one will often observe as many as four insects on a favoured tree. The bright sunlight is preferred, few going into the shaded parts for any length of time.
In the earlier part of the mornings it is possible, with caution, to get sufficiently close to place a pill-box over the insect, and many were caught in this way. As the heat of the sun increases, they become so
extremely active that sweeping quickly up the trunk with the net must be resorted to. On alighting Ophrynopus invariably runs up the tree and the upward sweep becomes the only sure way of making a capture.
After a rapid flight, an insect will alight in front of the observer and commence its search for a place in which to ovipost. The insect shows much activity, ascending the tree in stages, tapping lightly with the antennae as it goes. Rapid, short runs, with antennae tapping with equal rapidity, bring it to a place selected as being suited for the act. Much minute examination of the immediate area takes place, some insects being engaged as long as a minute and a half in their survey. Finally this small space is limited to one particular spot where the individual stands, and as if to test the position to the fullest degree remains perfectly still, with the antennae now moving less rapidly, each touching the place alternately and very lightly.
There follows an interval in which the wasp shifts its position forward a little, and raising the abdomen very slightly, projects the ovipositor on to the selected spot. The form of the last abdominal sternite allows the ovipositor to assume an almost vertical position to the abdomen, and the insect moves back until this is secured. Flexing itself and using its legs to the fullest advantage in moving the body, it now, by sinuous movements, gradually introduces the ovipositor until three-quarters of its length is in the wood. Then a more gentle probing takes place, while slowly a large opalescent sac is extruded behind the ovipositor. It is almost suggestive of preparing a suitable medium in which the larva that will shortly hatch will spend the first part of its life cycle, or may possibly assist in the correct incubation of the egg, whilst there is the further possibility that this is an air sac only, used in forcing the egg down into the wood Pulsating rhythmically for about twenty seconds, the sac is finally retracted into the body, to the accompaniment of the withdrawal of the ovipositor. No force is required in freeing itself and almost immediately the active search is again resumed.
When disturbed this wood-wasp will often stand still, but more frequently jumps rapidly from the tree and flies off.
The insects associated with Ophrynopus are mainly other Hymenoptera, and Coleoptera. Among the Hymenoptera two solitary wasps are common, Salius conformis Smith and Salius fujax Fabricius; both are gaudy insects, and are to be found hunting spiders in the interstices of the trees.
Higher up where shot-holes caused by timber-boring beetles are numerous, Rhopalum carbonarium Smith, in company with Tachytes sericops Smith, continually search these tunnels, disappearing therein for several seconds.
The beetles are too numerous to mention in detail, but three weevils, Psepholax sulcatus White, P. coronatus White, P. barbifrons White, are mentioned because of their presence in proportionate numbers with Ophrynopus, and of the likelihood of their being possible hosts, though on the other hand it is contended that Ophrynopus has a wood-boring and not a parasitic larva.
In June 1925, one tree was thoroughly examined by being split into fragments, but no sign of the wood-wasp's larvae or pupae were
found, hence development probably takes place towards the late spring.
Since writing the foregoing, a specimen of O. schauinslandi of which the writer had no previous knowledge, has been returned to the Cawthron Institute collection. This is an example taken by Mr. A. Philpott at Greenhills, 7th January, 1920.