Abstract
This paper deals with the effect of the water content of rice and the temperature on the velocity of development and the rate of reproduction of eight strains of two species of the rice weevils, Calandra oryzae L., C. sasakii TAKAHASHI. Each strain of C. oryzae was obtained from Japan (JL), Australia (AL), Indonesia (ID) and Missouri in U.S.A. (UM), and that of C. sasakii was from Japan (JS), Australia (AS), Nepal (NE) and Canada (CA).
Generally, the higher the water content in the range from 12.2 to 16.7%, the faster the velocity of development. The influences of water content on the velocity of developments of JL, AL, CA, and NE were greater than these of ID, UM, JS, and AS.
Similar inclination was observed on the rate of reproduction of each strain. There are two types on the influences of water content, one of which is independent on the change of water content, and another is not so. It seems that the former type belongs to the type of storage infestation and the latter that of the cross infestation.
At the temperature of 20, 25, 30°C the days necessary for the development of C. sasakii was slightly longer than that of C. oryzae. Developmental zero point of C. oryzae calculated by theoretical method was comparatively lower than that of C. sasakii without exception, but the totalt effective temperature of C. sasakii was significantly lower. The rate of reproduction of C. oryzae decreased with the increase of temperature between 25°C and 30°C, but increased for C. sasakii.
On C. oryzae, the developmental duration for female was shorter than the male at each temperature. On C. sasakii, however, the male was shorter, except at 30°C. Therefore, there appears to be considerable specific difference between these two rice weevils in regard to effects of temperature.
