1957 年 1 巻 4 号 p. 226-237
During these years the frequency of application of insecticides in apple orchards has increased in order to maintain a satisfactory control. This has been considered to be perhaps due to the appearance of resistant strain of insects to insecticides and, in certain cases, to an adverse effect of insecticides on natural enemy populations. This leads to a more intensive use of insecticides; as the result apple growers generally are applying a complex schedule of sprays. To develop additional information on the direct and indirect effects in the different number of spray applications upon the structures of arthropod communities, an experiment was conducted in an adult apple orchard. This kind of study was began by the author in 1956 and is now being continued. The present article is the first report on these experiments.
Basically, the plan of the experiments carried out in the present paper is simple. The orchard used consists of about 180 trees of 15 rows including a small number of young trees. But mostly it consists of 30 year old trees of the Jonathan and Ralls varieties. Insects and mites were kept under the schedule of 11 sprayings on half of the trees and 9 spray applications on the remaining half. In this case two check trees were selected in the center part of the west side in the orchard. Each spray plot was given a treatment of mineral oil emulsion as the ground spray, and then lime-sulphur alone, lime-sulphur plus DDT, lime-sulphur plus lead arsenate, lime-sulphur plus lead arsenate plus EPN and Bordeaux mixture during the period from early April to mid-August. Counts, both on insects and mites, were taken at intervals of 7 days from each 4 trees of the spray plots and 2 trees of the check plot. Insects collected by hand sampling and sweeping of 100 times within 1 square meter areas at the height of 1.5 meters above the ground in each survey tree, but in making counts of mites, 200 mature full sized leaves were picked at random and the number of various stages of mites was recorded.
Compositions of arthropod communities in each plot during the course of the present experiment are shown in Table 1. Of the 10, 659 individuals obtained throughout the entire season, 46.8 per cent was observed in plot of the 11 spray schedule, while remaining number was found in the two plots of 9 spray applications and the unsprayed at the rates of 28.3 and 24.9 per cent respectively. So far as the present data are concerned, it would seem that as the number of spray applications increase the greater is the population density.
As will be seen in Tables 2-4, based upon the seasonal changes of all the species composing the faunae, the seasonal succession of arthropod communities can be divided into following several groups:
Myzus malisuctus→Metatetranychus ulmi·Myzus malisuctus→Lithocolletis ringoniella·Metatetranychus ulmi on the plot treated by the 11 spray schedule; Metatetranychus ulmi·Myzus malisuctus·Eriosoma lanigera→Metatetranychus ulmi→Lithocolletis ringoniella·Metatetranychus ulmi (Lithocolletis ringoniella·Chlorita flavescence from late September) on the plot of 9 spray applications; Cacoecia xylosteana·Phenacoccus aceris→Myzus malisuctus·Metatetranychus ulmi→Metatetranychus ulmi·Lithocolletis ringoniella→Lithocolletis ringoniella·Metatetranychus ulmi (Lithocolletis ringoniella from late September) on the unsprayed plot. From the results illustrated here, it is clearly perceived that although there was no noticeable difference between the former two spray plots in the structures of community accompanying a high population through the entire season, the organization in the case of the later one, was rather complex having a poor number. Furthermore, as has been already shown in Tables