For some years now a device has been under development at the New Zealand Forest Research Institute, the purpose of which is to study the effects of sub-lethal amounts of stomach poisons (but also of fumigants and contact active materials) on the co-ordinative abilities of a cerambycid larva. This insect is Prionoplus reticularis - indigenous to New Zealand its larvae feed in decaying logs and are very common in Pinus radiata plantations. The intention of the programme has been to speed-up the screening of potential wood preservatives, deriving reproducible toxicity data in the fastest possible time. The machine itself, now termed a „repentiometer“ for lack of a better name, has been fully described elsewhere (Cross - in press), but a brief resume will be given here. Essentially it consists of two contra-rotating belts, placed one above the other, between which a larva of 0.8 to 1.2 g weight attempts to crawl (Prionoplus larva have greatly reduced legs that serve no purpose in moving along; crawling in tunnels is achieved by rhythmic turgor changes along the body). Since at this stage in its life the insect is intensely thigmotactic, i.e. will squeeze into any confined space offered rather than roll around free, there is no difficulty in getting them into the correct position. However, considerable electronic sophistication is needed to keep them there once the belts are moving, the speed of rotation being adjusted through two means, i) if the larva overtakes the belts the voltage to the driving motor is stepped up by a factor of 10, so forcing the larva back, ii) if the larva slows relative to the belts and is pushed out backwards then it makes contact between two electrodes, this reduces voltage by a small amount while at the same time supplying a mild electrical stimulus to the insect. Having now arrived at the correct speed range, and with these feedback controls working reliably, the repentiometer functions very well. It provides a very sensitive method of examining the effects of toxicity on an intact insect system, whether the chemicals under test are force fed or injected directly into the haemocoel (Cross 1979).

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