Developmental consequences of water and temperature in the European corn borer – maize interaction

Maize plants were grown under four moisture regimes (wet to extreme deficit) and three constant temperatures (20°, 25 ° & 30 ° C) in a phytotron. Each plant was infested with one E-race European corn borer [Ostrinia nubilalis (Hubn.)] (ECB) egg mass at pollen shed. ECB development, location, and establishment were recorded over the course of 12 destructive sample dates (4/temperature). ECB developmental rates were not significantly affected by soil moisture treatments, but were significantly affected by temperature. In spite of successful establishment of four distinctly different soil moisture regimes, the maize stalk tissue water levels were not significantly different among soil water treatments. Instead, the maize plants exhibited accelerated leaf senescence in response to the water deficit conditions. Among the soil water treatments, differences were found in larval establishment, vertical distribution and dispersion, and feeding site selection; however, those effects were slight and could not explain the similarity in ECB developmental rates observed in these treatments. In maize, the larval environment within the stalk was effectively insulated from changes in the external environment by the plant's ability to maintain a relatively high and stable stalk tissue water content. Thus, large changes to the soil environment had essentially no effect on ECB development, though drastic consequences for the plant. This study indicates that ECB rates of development are relatively insensitive to changes in the soil water environment as well as the associated changes in the maize plant that accompany severe drought stress. The significance of these findings to insect modelling, crop physiology, and insect-crop interactions is discussed. RESUME Influences de l'eau et de la temperature sur le developpement d'Ostrinia nubilalis dans le systeme pyrale-mais Des plants de mais se developpent dans un phytotron dans 4 conditions d'humidite du sol (de la saturation a la dessication) et a 3 temperatures constantes (20°, 25° & 30° C). Chaque pied est contamine au moment de l'emission du pollen, par une ooplaque d'O. nubilalis Hubn. (ECB) de race europeenne E. L'installation, la colonisation et le developpement des chenilles sont notes lors de 12 periodes de prelevements destructifs (4 par temperature). La vitesse de developpement d'O. nubilalis est affectee par la temperature, main non par l'humidite du sol. Les 4 niveaux d'humidite du sol n'ont aucun effet sur la teneur en eau des tiges de mais. En fait, les feuilles de mais presentent une senescence precoce lorsqu'il y a deficit en eau dans le sol. La teneur en eau du sol agit sur l'installation, sur la distribution verticale, la dispersion et le lieu d'alimentation des chenilles; mais ces effets sont legers et ne modifient pas la vitesse de developpement. L'environnement larvaire dans la tige de mais est efficacement isole des variations externes par l'aptitude de la plante a maintenir la teneur en eau des tiges relativement elevee et stable. Ainsi, des changements importants au niveau du sol n'ont pratiquement pas d'effets sur le developpement d'O. nubilalis, malgre les consequences brutales pour la plante. Cette etude montre que la vitesse de developpement d'O. nubilalis est relativement insensible aux modifications de la teneur en eau du sol ainsi qu'aux effets de ce stress de secheresse severe sur le pied de mais. La discussion porte sur l'importance de ces resultats pour la modelisation de la dynamique de l'insecte, la physiologie de la culture et les interactions entre insecte et plante.