Will the wasp work?

Press, 24 January 1986, Page 10

Will the wasp work?

A parasitic wasp, originally from the Mediterranean region, is showing promise in controlling the lucerne pest sitona weevil at sites in Canterbury. But it is too early to say whether Microctonus aethiopoides, the formal name of the wasp, will successfully control sitona weevil, says a M.A.F. entomologist at Lincoln, Dr Stephen Goldson. “It is looking promising at this stage, though it is always difficult to predict the effect of biological control agents,” he said recently. The wasp lays its eggs in the adult sitona weevil and these eggs hatch into grubs which eat the host, preventlng~it from reproducing and finally killing

Sitona weevil is a pest

of lucerne and other medics and it was first found in New Zealand in 1974 and is now widespread. Both the weevil and the larvae of sitona attack the lucerne plant and severe yield reductions can occur. The small black wasp was introduced into New Zealand by the D.S.I.R. as a possible control for sitona in the spring of 1982. After a full quarantine, to ensure the wasp had no parasites of its own and that it only attacked sitona, the wasp was released at sites in Canterbury. A survey carried out during February last year found that 20 to 30 per cent of sitona weevils contained the wasp larvae during the weevil’s summer dormant period. This was described by

Dr Goldson as promising. The weevil and the wasp have complicated interlocking life cycles, adapted to the Mediterranean climate from which they both came. The wasp build-up is being monitored by the M.A.F. and the D.S.I.R. and once the life cycle is . fully understood, the parasite will be introduced to new sites in Canterbury where the effects of sitona have been closely observed for years. This should pro- < vide valuable “before ' and after” information, Dr Goldson said. It was important to determine what value ; microctonus aethiopoides ' has as a biological con- ' trol, he said, as the pesticides which are now - used to control sitona ] would also control the < wasp.