NUCLEAR POLYHEDROSIS-VIRUS OF THE EUROPEAN PINE SAWFLY, NEODIPRION-SERTIFER (GEOFFR) (HYM, DIPRIONIDAE) RETAINS INFECTIVITY IN SOIL TREATEDWITH SIMULATED ACID-RAIN

The effect of simulated acid rain on the infectivity of the nuclear po lyhedrosis virus of the European pine sawfly, Neodiprion sertifer (Geo ffr.) was studied in southern Finland. Three-year-old saplings of Scot s pine, Pinus sylvestris (L.), were sprayed once with diluted N. serti fer virus nuclear polyhedrosis (NsNPV) suspension or distilled water; after this they were irrigated during the growing season with ground w ater (pH 7) or with acidified water of pH 4 or pH 3, adjusted by addin g both H2SO3 and HNO3. The ability of virus-killed N. sertifer larvae to shelter viruses was tested by killing larvae with NsNPV on half of the virus-treated saplings before the beginning of the irrigation trea tments. The persistence of the virus on the foliage and in the soil wa s tested the following summer by two separate bioassays with European pine sawfly larvae. In the first bioassay, in which larvae were fed on ce with the foliage of the experimental saplings, no significant diffe rence in mortality among the various treatments was detected. In the s econd bioassay, in which larvae were fed on pine foliage contaminated with soil from the virus-treated saplings, virus treatment had a signi ficant effect. In that case, only 4-7% successfully formed cocoons, co mpared to larval survival of 22% in the absence of the virus. Of the l arvae fed with pine twigs contaminated with soil from saplings on whic h virus-infected larval cadavers were retained, the mortality rate was 100%. Acid rain treatments did not affect larval survival in either b ioassay. Thus, NsNPV infectivity in the held is maintained in the soil but not on the foliage and appears to be unaffected by simulated acid rain.