Simulation-Models for the Phenological Development of Mythimna-Convecta (Walker) (Lepidoptera, Noctuidae)

Abstract

Larvae of armyworm, Mythimna convecta, were reared under fluctuating temperatures (1-7-degrees; 3-13-degrees; 7-17-degrees; 11-24-degrees; 31-39-degrees-C). Data from these trials were combined with previsouly published data derived from constant-temperature studies (ranging from 15-degrees to 33-degrees-C) to model the effects of temperature on development rate. Temperature-dependent development rates for each of eight immature stages were described by one of three non-linear functions and by a linear model modified to improve the performance about the lower and upper temperature extremes. At the lower and upper thermal limits (< 11-degrees-C and > 33-degrees-C) of the species, survival of larvae under fluctuating temperatures was greater than recorded in previously published studies under equivalent constant temperatures. A serious constraint on fitting a model to the later larval instars was the inconsistent appearance of a seventh instar. The two sets of models were evaluated against field development in three winter and one summer experiments. The modified linear model, with capacity to manipulate predicted development at threshold temperatures, provided a marginally better prediction than did the non-linear model. The sine wave method for estimating diurnal temperatures from minimum and maximum temperatures was shown to produce overestimates of development rates. A correction factor for the seasonal conditions in western Victoria was provided.