Temperature thresholds and thermal requirements for the development of the rice leaf folder, Cnaphalocrocis medinalis

Abstract

The rice leaf folder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) is a predominant foliage feeder in all the rice ecosystems. The objective of this study was to examine the development of leaf folder at 7 constant temperatures (18, 20, 25, 30, 32, 34, 35° C) and to estimate temperature thresholds and thermal constants for the forecasting models based on heat accumulation units, which could be developed for use in forecasting. The developmental periods of different stages of rice leaf folder were reduced with increases in temperature from 18 to 34° C. The lower threshold temperatures of 11.0, 10.4, 12.8, and 11.1° C, and thermal constants of 69, 270, 106, and 455 degree days, were estimated by linear regression analysis for egg, larva, pupa, and total development, respectively. Based on the thermodynamic non-linear optimSSI model, intrinsic optimum temperatures for the development of egg, larva, and pupa were estimated at 28.9, 25.1 and 23.7° C, respectively. The upper and lower threshold temperatures were estimated as 36.4° C and 11.2° C for total development, indicating that the enzyme was half active and half inactive at these temperatures. These estimated thermal thresholds and degree days could be used to predict the leaf folder activity in the field for their effective management.

Figure 1.

Percent survival of different larval instars of Cnaphalocrocis medinalis at 7 constant temperatures. High quality figures are available online.

Figure 2.

Cumulative emergence of Cnaphalocrocis medinalis adults at each constant temperature. High quality figures are available online.

Figure 3.

Linear and non-linear thermodynamic OptimSSI model fitted to the temperature dependent development of Cnaphalocrocis medinalis. Circles indicate data points. Open circles indicate data points outside the range of the linear model. The curved line indicates the values of developmental rate predicted by the OptimSSI model, whereas the straight line denotes the values of linear fitting. The 3 open squares denote the predicted mean developmental rates at T^L, T^Φ, and T^H. High quality figures are available online.