STUDIES ON THE DISPERSION OF THE MULBERRY SCALE, PSEUDUALACASPIS PENTAGONA

Abstract

The distribution of the female adults of the mulberry scale on each twig of the cherry tree, the plum tree and the mulberry tree was recorded, and the mortality and oviposition rates were surveyed to elucidate the phase of dispersion and its ecological significance ; on the other hand in the laboratory condition of 25℃, the number of eggs laid on the tuber of the potato by a female adult and the phase of dispersion of the nymphs hatched from these eggs were surveyed. The results are : 1) The individual number of the female adults settled on each twig suits the following equation, which was first proposed by KETTLE(1951), log y = log a +bx, where y represents the individual number at the distance x from the crotch of the twig. 2) The number of eggs laid by a female adult at a constant temperature of 25℃ was 99.7 on an average, while in the field 11 on an average of the nymphs from a female adult settled on the twig of the mulberry tree. Accordingly the mortality in the course of the dispersion was estimated to approach 89 per cent in the field. 3) The mortality of the female adult was about 30 per cent on an average (including the sterile female) from the settlement on the twig to the oviposition time, and it was higher towards the center of the dispersion. 4) Although no relations were recognized between the number of the eggs embraced by a female adult and its settling position on the twig, the rate of the sterile female adults were higher near the crotch of the twig and accordingly the oviposition rate on the whole was lower there. 5) The sex ratio, ♀/(♀+♂), of the nymphs which were laid by hibernated female adults was higher the top of the twig.