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(I) Miscellaneous. (1) Iris Mosaic— This disease, of virus origin, has been identified as causing serious losses in bulbous iris. (2) Pyrethrum production—blowers with high pyrethrin content can be secured by growing selected clonal lines, as has been shown by further analyses. Work is being undertaken to ascertain the effects of locality on the pyrethrin content. Flowers have been harvested from ten selected pure clonal lines growing at Auckland, Ruakura, and Palmerston North, and samples forwarded to the Dominion Laboratory for analysis. Plots containing three strains of pyrethrum have been established at nine localities in the North and South Islands to test further the effect of locality on pyrethrin content. (3) Kumara Varieties.—For the purposes of ascertaining the best varieties for cropping, culinary purposes, and disease resistance all available lines have been imported from Australia, 1 acific Islands, and the United States of America and grown at Owairaka. Those grown differ markedly in leaf character and growth habit, and when harvested will doubtless display wide differences in type of tuber. The two varieties grown in New Zealand —Tauranga Red and Blackberry were at first more vigorous in growth than any of the imported ones ; but, with the advent of warmer weather some of the latter are now equally vigorous. ENTOMOLOGY DIVISION. Director: D. Miller. Diamond-back Moth and White Butterfly in New Zealand. The researches upon these two insects have been concerned with their ecology and parasitic, control. In regard to the ecological aspect, the principal avenues of investigation are (1) The recording of the variation in population density of the insects in the field throughout the year in relation to associated climatic factors. (2) Laboratory studies under controlled conditions of the climatic factors promoting or preventing epidemics of the insects. The 1938—39 season has been remarkable for the low level of population of the insects in field crops, and many of the crops are in poor condition due to lack of rainfall. The work so far has been principally directed towards determining their distribution within the crop so as to enable the development of an accurate sampling technique which can later be used for periodic estimates of population density on one crop throughout the season. Attention has also been given to the methods of recording climatic factors in the area under observation. Some preliminary experiments have been made with the object of determining the relative weights of food consumed by the diamond-back moth and the white butterfly. The white-butterfly larva, being much larger than that of the diamond-back moth, consumes more food and does more damage. In comparing the relative importance of the two insects it will thus be necessary to apply a food-weight factor to the population densities. Diamond-back Moth. A point which emerges from the investigation is that in the early stages of infestation by diamondback moth the population appears to be significantly larger on the margin of the crop than m the centre, and this complicates the taking of an accurate sample. In the later stages of an infestation, when the population density is higher, it appears that the population density is fairly even over the whole of the field. In the crops which were surveyed in the Wairarapa the population density of both diamond-back moth and white butterfly has been low this season and little damage has been done. The same position is reported to occur in Canterbury. In Hawke's Bay on some crops the diamond-back moth population was higher than any seen in the Wairarapa, but even so little damage was done. In Hawke's Bay in February many of the crops were severly damaged by the cabbage aphis, and this later appeared in the Wairarapa to a lesser extent. The behaviour of adult diamond-back moths under the influence of various feeding solutions has been the basis of a series of experiments carried out during the winter months. It has been found that moths fed on suitable solutions can live for over a hundred days. Throughout this period eggs were laid whenever the atmospheric temperature was moderately high, and moths mated freely during the first few weeks of confinement in the experimental tubes. These results show that the moth is able, under certain conditions of climate and nutrition, to survive the colder months of the year in the adult state. Whether or not these conditions can be expected in the field has not been determined, and the prospect of survival of any eggs or larva) hatching from them must form a basis for further experimental work. These points lead to a determination of the means by which the parasites, which are primarily dependent for their existence on the moth m its various stages, are able to overwinter. With reference to the researches into parasitic control, against the diamond-back moth two parasites are being utilized at present—the pupal parasite (Diadromus coUaris) and the larval parasite (Angitia cerophaga). Another larval parasite (Apanteles plutellae) was imported, but failed to develop. In the case of Diadromus collaris sufficient supplies for study were first reared in the laboratory from the small amount of material that survived the journey from England, with the result that approximately 50,000 adults have been bred during the period under review ; of this number some 24,000 have been liberated in various localities and the remainder held for laboratory studies.

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