Plant Architecture, Hail Nets and Thermal Behaviour Influencing Developmental Rate and Modelling of the Codling Moth

Abstract

Changes of plant architecture result in a considerable alteration of the microclimate within orchard trees with effects on insect pest development. Consequently, such changes require adjustments in modelling phenology. Thermoregulation by choice of preferred sites within the habitat also influences insects’ body temperature and thus development. We investigated how tree shape of apple trees (high stem/dwarf) and the use of hail nets influence solar radiation and temperature within the habitats of a key pest in apple – the codling moth (Cydia pomonella L.). Furthermore, we examined whether distinct codling moth stages perform thermoregulation behaviour. Plant architecture parameters (leaf area index and global site factor), radiation intensity, and habitat temperatures were quantified in high stem and dwarf apple trees. Air temperature was assessed within the canopy, and surface temperature was determined on tree bark and apple fruits. Results from dwarf trees compare to high-stem trees as follows: The lower leaf area index of dwarf trees resulted in a higher radiation energy transmission. Air temperature within the canopy of dwarf trees was higher during daytime and lower at night. Surface temperature of bark was generally higher, while that of apple fruits was higher on sunny days, but cooler on overcast days. Hail nets reduced radiation intensity and air temperature within the canopy. The thermal response of mobile stages of the codling moth was examined in temperature gradient experiments. Feeding larvae preferred apple regions with higher temperatures, while mature larvae showed no temperature preference in cocooning sites. Adult moths responded negatively thermotactic, but females strongly preferred areas with higher temperatures as oviposition sites. The impact of plant architecture and hail nets on the developmental rate and seasonal cycle of C. pomonella is discussed.