Development response of Spodoptera exigua to eight constant temperatures: Linear and nonlinear modeling

Temperature-dependent development of Spodoptera exigua (Hubner) were evaluated at eight constant temperatures of 12, 15, 20, 25, 30, 33, 34 and 36 degrees C with a variation of 0.5 degrees C on sugar beet leaves. No development occurred at 12 degrees C and 36 degrees C. Total developmental time varied from 120.50 days at 15 degrees C to 14.50 days at 33 degrees C. As temperature increased from 15 degrees C to 33 degrees C, developmental rate (1/developmental time) of S. exigua increased but declined at 34 degrees C. The lower temperature threshold (T-min) was estimated to be 12.98 degrees C and 12.45 degrees C, and the thermal constant (K) was 294.99 DD and 311.76 DD, using the traditional and Ikemoto-Takai linear models, respectively. The slopes of the Ikemoto-Takai linear model for different immature stages were different, violating the assumption of rate isomorphy. Data were fitted to three nonlinear models to predict the developmental rate and estimate the critical temperatures. The Tmin values estimated by Lactin-2 (12.90 degrees C) and SSI (13.35 degrees C) were higher than the value estimated by Briere-2 (8.67 degrees C). The estimated fastest development temperatures (T-fast) by the Briere-2, Lactin-2 and SSI models for overall immature stages development of S. exigua were 33.4 degrees C, 33.9 degrees C and 32.4 degrees C, respectively. The intrinsic optimum temperature (TO estimated from the SSI model was 28.5 degrees C, in which the probability of enzyme being in its native state is maximal. The upper temperature threshold (T-max) values estimated by these three nonlinear models varied from 34.00 degrees C to 34.69 degrees C. These findings on thermal requirements can be used to predict the occurrence, number of generations and population dynamics of S. exigua. (C) 2014 Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society. Published by Elsevier B.V. All rights reserved.