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32. Log Volume Tables. —Log volume tables for insignis pine and Corsican pine in Southland Conservancy were issued. Extensions were made to the Rotorua Conservancy log volume table for insignis pine to show volumes for lengths up to 50 ft. and small-end diameters up to 24 in. Certain defects revealed in the use of these tables indicate that the original table requires careful testing. Forest Pathology Research 33. Entomology.—The major entomological problem during the year has been the study of Sirex noctilio, known sometimes as the steel-blue sawfly or wood wasp, which has been causing considerable damage in pine forests, and this insect is separately reported on below. In the silviculture of the New Zealand beech there are several insects about which information is being collected. The most important of these is Nascioides enysii, which kills trees at any age through the feeding of the larvae in the cambium region. Predisposing factors are of outstanding importance. Another important insect is the ghost moth (Charagia virescens) the larvae of which tunnel the wood of beech and othei hardwood. This insect occurs only in the North Island and its control is necessary if silviculture is to be practised in the area. Navamorpha lineatum, an insect attacking Douglas fir, has been the subject of a study which has revealed that damage to the twigs by cicada or other agency is not necessary for successful oviposition. Bud scales at the base of the new season's shoots are frequently selected, but oviposition can be successfully accomplished even when no growth has taken place. 34. The Sirex Problem. —Broadly speaking there has been a decrease in the incidence of Sirex noctilio in the forests of Rotorua Conservancy where it had developed so conspicuously since 1946. Locally it has been very abundant and its attack severe, but conditions during the summer, although dry, were less favourable to Sirex than in recent years. The rainfall in the principal forest areas during the critical period was very little short of the average for the past thirty-five years. Dry periods occurred, but at no time were drought conditions experienced. 35. The insignis-pine forests maintained a generally good appearance and it is expected that the trees will be able to resist Sirex attack. Stands where mortality took place previous to 1949 now show tufts of dark-green foliage, a feature that is interpreted as indicating recovery of vigour and benefit from the increased root space resulting from the casualties. It was found that in the majority of infected trees examined only a small proportion of the larvae have developed. A new factor that has come into play is the absence of small and suppressed trees in areas where there was heavy mortality last year ; so there is now a relatively large Sirex population and a shortage of trees suitable for successful attack. It was possible that the Sirex would therefore migrate to more suitable sites, but no appreciable migration has been observed, the Sirex attacking the trees which remained alive. A new feature is the attack and killing of large branches of marginal trees on which the living branches extend to the ground. 36. A technique for breeding Sirex under conditions of controlled temperature and humidity has been evolved, making it possible to secure Sirex when required for development of parasites from the Northern Hemisphere. Rhyssa persuasoria reared in the insectary have been liberated in forest areas. This parasite of Sirex has been recovered in forests in which they were released some years ago. Negotiations are in progress for introduction of Ibalia leucospoides to supplement the effects of Rhyssa in limiting the Sirex population. The first importations took place soon after the close of the year. 37. Chemical control of Sirex has been given considerable attention. Tests of D.D.T., toxaphene, benzene hexachloride, chlorodane, and rothane, using Sirex as a test insect, gave no indication that these insecticides would be effective under field conditions. It is possible that by strictly controlled experiments with a large variety of insecticides, solvents, and carriers, an effective chemical control for Sirex may be

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