Studies on breeding and control method of citrus ground mealy bug, Rhizoecus kondonis KUWANA

Abstract

1. Using breeding veils for soil insect, the authors bred citrus ground mealy bugs to know their ecological characters, and investigated relationship between their density and the presence of straw mulch under mandarin orange trees at the damaged orchard, and also their resistibility against agricul-tural chemicals, to propose their effective control method suggested by results of these experiments.
2. The optimum margin of temperature and water content of saw-dust where the bug is bred (shown in percentage against water capacity) was found to range between 15_??_25°C of temperature and 27.6_??_52.5% water content, and its range was comparatively narrow.
In case of wireworms (Melanotus caudex LEWIS) breeding, it ranged between 10_??_25°C of temperature and 27.6_??_89.4% of water content; in case of Japa-nese beetles (Popillia japonica NEWMAN) in larval stage, it was between 10_??_30°C of temperature and 19.1_??_93.1% of water content.
The optimum temperature to breed citrus ground mealy bugs was the middle between both kinds of species, but the condition where water content of saw-dust is exceedingly less than in cases of both insects was suited to breeding of this one.
3. As water content of saw-dust increased the mortality of this insect increased, and in case of 100% water content no living insect completely existed in saw-dust; on the other side they came up to soil surface when the water content increased than 52.5%; and its tendency was remarkable as water content increased.
4. Because injurious insects died as water content increases, the authors investigated water content of soil under rotten straw mulch at damaged orchards. Water content of these soils showed nearly 100% even a few days after rainfall, which leads the authors to presume that the straw mulch over, the orchards is useful to control this insect.
5. Experiments on suspected relation between their density and the presence of straw mulch were carried out. In case of covering the whole orchards with straw mulch, the density of this insect was much less than that of no covering at the same damaged field; its damage was rather negligible.
6. In Fujieda district (Shizuoka Prefecture), damaged orchards were situated only at a slope land, and their management was bad: there was scarcely any cover of straw mulch, mandarin orange trees spread their shallow roots just under soil surface, and tea trees were planted under them.
7. The resistibility of this insect against agricultural chemicals was very weak; the insecticidual effects of calcium cyamide and tobacco dust were comparatively strong.
8. The authors suggest the following method for its successful controlling. After cleaning the soil surface of damaged orchards, and dusting with non-phytotoxicitic insecticide having a long residual-effect, the whole surface of orchards must be covered with thick straw mulch, because the insect con-cerned dies or comes up to the soil surface with increase in water content of soil.