Identification of resistance in Malus against codling moth and leafroller

The tree fruit industry is one of the biggest industries in Washington State, producing annually crops valued over $2 billion and having an impact on the state’s economy of over $6 billion. Washington growers annually produce 5.5 billion pounds of apples valued over $1.4 billion, representing nearly 70 percent of Washington’s tree fruit industry.

The obliquebanded leafroller (OBLR), Choristoneura rosaceana, and codling moth (CM), Cydia pomonella, are two of the most important insect pests of apple in Washington, causing damage by feeding on leaves and fruits, respectively. The majority of insecticides applied to apple is for control of OBLR and CM. Pesticide usage defeats biological control efforts, incurs risks to farm labor and the environment, and evolves resistance-development and cross-resistance to insecticides throughout North America.

A whole-leaf bioassay method was developed that provided high apple-leaf quality over time. Development rates and mortality of OBLR larvae reared on an artificial diet provided the data and a timeline against which larval performance on different apple (Malus) varieties could be evaluated. OBLR larvae feeding on different Malus genotypes showed variation in development time, pupal weight, fecundity, and mortality. Pupal weight was inversely correlated with development time. Malus genotypes that negatively impacted larval survival and development showed both negative and positive impacts on fecundity.

This project will provide key information to the Washington Apple Breeding Program for selecting parents with resistance against OBLR and CM. The long-term impact will be a reduction in the use of insecticides and the enhancement of biocontrol.