On the Winter Mortality of Arrowhead Scale, Prontaspis yanonensis KUWANA

Abstract

The mortality of arrowhead scale attacking the citrus trees was studied for two winters during 1963-1965 at Nagasaki Prefecture. 689 individuals of immature adult females, 2251 of matured adult females and 2141 of male pupae were marked and observed since December 1963 to May 1964. The mortality during the winter were as follows; immature adult females 97 percent, matured adult females 84 percent and male pupae 97 percent. 506 individuals of immature adult females, 1930 of matured adult females and 960 of male pupae were marked and observed during January-May 1965. The mortality during the winter season were as follows; immature adult females 91.5 percent, matured adult females 95.3 percent and male pupae 97.8 percent. These data on mortality were compared with some other mortality records of this species investigated at various districts of Japan. Winter mortality of other districts varied between 50∼82 percent in immature adult females 10-90 percent in matured adult females. The winter mortality observed in Nagasaki Prefecture were higher than those of other districts. Age distribution of overwintering arrowhead scale in this orchard was examined during the same seasons. In early winter, various stages of living scales such as 2nd instar larvae, immature adult and matured adult of females, 1st instar larvae, 2nd instar larvae and pupae of males were found. During these winters, proportion of young larvae gradually decreased and at the beginning of spring, overwintering arrowhead scale populations chiefly consisted of matured adult females and pupae of males. These results coincided with the results obtained from some other districts.