H.—34.

During the 1935-36 season 79,000 parasites were distributed, as follows :— Canterbury .. .. ..30,095 Westland .. .. .. .. 1,460 Auckland.. .. .. .. 23,285 Wellington.. .. .. .. 1,340 Marlborough .. .. .. 9,850 Taranaki .. .. .. .. 300 Otago .. .. .. .. 8,060 Nelson .. .. .. .. 2,610 Total .. .. .. 79,000 Southland .. .. .. 2,000 Diamond-back Moth: A considerable amount of work in regard to this pest is being carried out both here and in England. From a report on a preliminary survey in connection with the moth and its parasites, it is pointed out that the moth is known in England mainly in epidemic form ; frequently it is not noticed and recorded by economic entomologists. A number of parasites have already been found in England, but a considerable amount of work remains to be done before any material can be sent out here. In New Zealand a considerable amount of time has been devoted to field surveys, life-history studies, and the existing host-parasite relationship. A detailed account of this work as far as it has progressed will shortly be forwarded. White Fly: Stocks of the white-fly parasite (Encarsia formosa) have been kept going throughout the year, and supplies of the parasite have been sent out to various applicants from time to time. This parasite when given time to establish proves a thoroughly effective check to the white fly. Red Mite : Further experiments were carried out, much on the same lines as those already reported in the Journal of Science and Technology, Vol. 16, No. 5, pp. 261-270 (1935). The purpose of the work was to ascertain as accurately as possible the value of applying winter oils against the overwintering eggs of the red mite (Paratetranychus pilosus) as a control for this pest. The technique of counting and observing results was the same as that used in the experiments already reported in the publication mentioned above. The results indicate that under the outdoor conditions neither increasing viscosity nor stability of emulsion have any significant increased killing-effect. The oils applied in July and early August had no killing-effect at all, whereas those applied in late August and September gave only about 40 per cent, kill due to oil, taking into consideration the percentage natural mortality, which was high, being in 75 per cent, of the trials approximately 40 per cent. The weather during the period for which the twigs were exposed in the outdoor cage was abnormally wet, and conditions were generally unfavourable to a good control by the oil. From experience in this work it would seem, when the eggs are exposed to outdoor conditions in this way, that the method of estimating results described in experiments already reported in the Journal of Science and Technology (mentioned above) might be investigated with advantage. If suitable supplies of eggs can be secured it is proposed to carry out such an investigation this winter, as this is necessary to interpret the results correctly. In conjunction with the above detailed work a fairly large field experiment was carried out on Delicious-apple trees in a Hastings orchard. Altogether 204 trees were included in the experiment, which was designed to test the effect of viscosity and stability of emulsion on the killing-power of winter oils on red-mite (P. pilosus) eggs. The oils were applied in early July on one block and in early September on a second block. The purpose of this was to discover also whether the time of application influenced the kill secured. In July and September overwintering eggs of P. pilosus were very plentiful on most of the trees, but at an inspection in the middle of December mites were extremely scarce on all trees, even on the checks, so that it was impossible to detect any difference between the effects of any of the oils. The season had been an extremely wet one, and apparently this accounted for the disappearance of the mites. Up to the present there seems to be little evidence to show that winter oils against P. pilosus give a good kill. Insecticides for controlling the White Butterfly (P. rapae) on Cabbages. —This work was continued at the area in the 1935-36 season. The insecticides tested were arsenate of lead sprays and dusts, calcium arsenate sprays and dusts, pyrethrum sprays, nicotine sprays, common-salt sprays, lettucedecoction sprays, and derris sprays and dusts. The results show the superiority of the derris dusts. The poison-residue problem is also being investigated thoroughly. This is of moment where arsenicals are used. Cabbages were sprayed at various times with lead arsenate and harvested at specified intervals after spraying. The samples have been forwarded to the Dominion Analyst for examination. Results so far show that, even if an interval of six weeks is allowed between the last spraying and the time of harvesting, there is a danger of more than 0-01 grain of arsenic trioxide per pound being present if the whole cabbage is analysed. On the other hand, if only the hearts of such cabbages are used, there is little more than a trace of arsenic present. The figure 0-01 grain of arsenic trioxide per pound of foodstuff was that adopted by the Royal Commission on Arsenical Poisoning in London, 1903. This figure is accepted in most countries, but in New Zealand the regulations under the Sale of Food and Drugs Act, 1908, s do not allow the'presence of any arsenic or lead at all on fresh cabbages and cauliflowers. The whole position is unsatisfactory as far as recommendations for the use of arsenicals are concerned, especially since lead-arsenate spray will give quite a good control of white-butterfly larvas. Therefore the present work is designed to clear up the position. This project should be finished after next season. Red Scale (Chrysomphalus aurantii). —In collaboration with the Horticulture Division an experiment on the control of red scale on lemons was carried out at Tauranga. The object of the work was to discover the nature of the control secured with summer oil at 1-33 on this pest. The 1934-35 season was a bad one for this scale, and growers claimed that it was very difficult to secure a control by oil spraying. The plots at Tauranga were sprayed at specified intervals, and a week to ten days after spraying samples of the sprayed fruit were forwarded to Palmerston North for examination as

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