The author studied on the morphology, nymph and adult stage, reproductive capacity, movement from above to under ground, wintering condition of under ground woolly apple aphid, influence of growth rate by root damage of apple tree at heart land of apple production in Korea, cytological change of root gall, resistance against apple stocks, reproductive rate according to the soil condition and quality, effect of biological control with Aphelinus mali and chemical control methods from 1965 to 1968. The results obtained were as follows;
1. Wingless adult female is elongated round with 12 segments and 6 segmented antenna. 1st and 2nd segments were shortened, thick and has sensory seta on every segments except 3rd segment. Tarsus was degenerated in the leg of woolly apple aphid.
2. There were little difference in the egg number, egg form and nymph number which were in the body of above and under ground woolly apple aphid. Form of ovary and number of ovariole was the same.
3. Nymph and adult stage were nearly the same between above and under ground woolly apple aphid. Nymph stage was about 17 days and 13 days were required for adult stage.
4. The number of nymph reproduced from adult was about 44 individuals from both above and under ground woolly apple aphid.
5. Seasonal occurence of above and under ground woolly apple aphid was decreased during hot spell, late July and increased again from September.
6. Large parts of woolly apple aphid had collected From above and under ground were inoculated above twig moved into the soil within 24 hours. Habit of movement into the soil and parasite at there were derived from toxic chemicals spray for a long time, the author believed.
7. Woolly apple aphid was wintered by nymph and adult stage at root gall and crack of the roots.
8. At heart land of apple production districts, about 40% were infested on the variety of American summer pearmain by under ground woolly apple aphid while in general, it is believed that woolly apple aphid parasite on the twig. Thus it was clarified at first in Korea by author that woolly apple aphid parasite more seriously at root of apple tree than above twig.
9. Influence of root damage affected trunk and shoot growth. Growth rate of the shoot in the most serious plot were 55.6, 26.4㎜ and 3.84㎜ in trunk, shoot length and shoot diameter.
10. Root gall is formed by piercing of stylet and cell at the point of piercing was more elongated than non-damaged root cell. Thus xylem portion of the root was corked.
11. The most resistant apple stock against woolly apple aphid was Malus prumifolia by 24 individuals.
12. Reproductive capacity was reduced considerably when applied chemical fertilizers; Acid soil suppressed their reproduction while highly increased in the plot of muck applied.
13. Biological control effect with Aphelinus mali was investigated at several districts near by Taegu city. The results showed nearly the same ratio with the results of about 30 years ago. Parasitic rate was about 50% and the lowest peak was observed in October.
14. The highest mortality showed at Metasystox among common insecticides and Hepta among soil insecticides. Upper part of the soil was the highest in the mortality at every chemicals treated. Soil insecticides are more effective than common insecticides. At various concentrations, recommended and higher concentration showed good results but it can be recommended to use the recommended concentration the author believed.
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