Threshold Temperature and Thermal Constants for the Development of Cotton Leaf Roller, Natarcha (Sylepta) derogata F_ABRICIUS (Lepidoptera: Pyralidae)

Abstract

Studies were made on the threshold temperature and thermal constants for the development of cotton leaf roller, Natarcha derogata FABRICIUS. The results are summarized as follows:
The threshold low temperature for development and total effective temperature were calculated from the result of rearing throught all stages as shown in the next table.
The relationship between developmental velocity (V) and temperature (T) was expressed as following liner equation.
EggV=0.0176 T-0.1805 Larva V=0.0038 T-0.0828 Pupa V=0.0075 T-0.0828 All stages V=0.00224T-0.02642
Under the constant environmental condition of 25°C and 75-90% humidity, the larvae were reared separately on fresh leaves of the Firmiana platanifolia SCHOTT et ENDLE. The larva passed through 6 instars in a generation, and the mean width of head capsule ranged from 1st to 6th instar as 0.24, 0.41, 0.76, 1.23, 1.9, 2.23mm respetively. And the ratios of the same width between succeeing instars were similarly 1. 71, 1.85, 1.62, 1.37 and 1.32.
The relations of log-width of exuviae of head capsule to instar number were found to berepresented generally by two straight lines intersecting at a point of the 4th instar. The larval instar (X) was related to the head capsule width (Y) by the following equation.
lst-4th instar: log Y=2.14+0.24X 4th-6th instar: log Y=2.573+0.13X