Host–Pest Interactions: Investigating Grapholita molesta (Busck) Larval Development and Survival in Apple Cultivars under Laboratory and Field Conditions

Abstract

Phenology models are widely used in Decision Support Systems to predict the phenology of pests. Grapholita molesta (Busck) (Lepidoptera: Tortricidae), a polyphagous pest, has a high prevalence in apple trees (Malus domestica Borkh.) (Rosales: Rosaceae) in certain areas, despite the fact that apple trees are considered secondary hosts. Its natural behavior of feeding inside plant tissue at the larval stage makes monitoring and planning methods of control critical for Integrated Pest Management. The development times and survival rates of two field populations of G. molesta larvae on apple cultivars ‘Gala’, ‘Golden’, and ‘Fuji’ were determined under different temperature (constant versus field fluctuation) and feeding conditions (diet versus apples attached to the tree and detached from the tree). The results showed that G. molesta fitness in apples is affected by fluctuating temperature regimes in the field, the condition of the fruit, whether or not the fruit is attached to the tree, and the cultivar. The temperature was the main cause of the differences in the studied parameters. Larvae development time was delayed due to fluctuating field temperatures. Larvae had a shorter development time in fruits detached from the tree compared to attached fruits, and apple cultivars influenced development time in both laboratory and field conditions, with the ‘Golden’ cultivar having better fitness and a higher rate of larvae survival in the fruits attached to the tree. These factors need to be considered to properly adjust the phenology models and improve the Integrated Pest Management system of apples.