Vergara - 1976 - Physiological and morphological adaptability of ri

CLINIATE AND RICE INSECTS 371
2. [sodevelopmental zonatitm of Laodelpliar srriarellzis
in
Japan.
L. sn-iatellus. a northern species. is also distributed in Taiwan and the Philippines.
but in the latter. distribution is restricted to cool and elevated localities.
ll multiplies much more on wheat and weeds such as [Jigitaria and Loliun:
during spring and autumn than on rice in summer, while N. cincriceps multiplies
preferentially on the rice plant in summer.
The law of total effective temperature is not applicable when temperature
fluctuates below or around the developmental threshold as mentioned by Messenger
(1959). l-lokyti (1972) found that with N. cincticeps. accumulated daydegrees
above 12°C (tentatively fixed as the threshold for posl-diapause development
instead of 13.3°C for non-diapausing development) from January‘ l. and
50 percent molting date of the ovcriariiiteriiig fouith-instar nymph showed a
clear linear regression. This served as a forecast of the date of molting of the
fourth-instar nymph and that of the date of emergence of ensuing adults. Daydegrees
D(x) until a certain date (x) were calculated as tollovys:
D(x) = (Max temperature at >< — l2.0)/2(Max(x) - Min[x))
Actual dajv-degrecs in the field were 5 to l5_ while under constant temperature
in the laboratory‘. 50 to 60. meaning that post-diapause nymphs can grow while
accumulating minor temperature around the threshold in the field. On the other
hand. day-degrees for the fifth-instar nymph were about 50, showing a fairly
constant value for various years.