Deciduous tree fruits such as pears and apples are widely grown in the Pacific Northwest of the United States and are well adapted to the seasonal environment in that region. Extended cold periods provide adequate chilling to break dormancy and reinitiate growth in the spring. Cold exposure synchronizes the physiological processes and makes sure that bloom is uniform and that fruit matures in a uniform manner. As a result of global warming, some fruit-growing areas may experience inadequate cold exposure during the winter months, gradually shifting the southern boundary for production of deciduous fruits further north. However, climate change will affect not only growth and fruiting habits of fruit trees but also the insect and mite pests which feed on them. There is general agreement that in temperate regions a trend towards warmer summers and milder winters will generally benefit insect and mite pests and increase their injuriousness. Temperature changes in particular will impact the development, mortality, phenology, and voltinism of fruit pests. Here we discuss how climate change may affect pests and control practices on deciduous tree fruits in the Hood River Valley of northern Oregon. This small valley extends in a north-south direction from the Columbia River to the foothills of Mt. Hood and is characterized by a varied topography and large altitudinal differences (sea level to 600 m). The major pest of pears and apples in that area is codling moth, Cydia pomonella L., a cosmopolitan pest which is present in most deciduous fruit-growing areas of the world. Like its host trees, the codling moth is well adapted to a seasonal environment. Diapause is the principal mechanism which synchronizes its phenology with the tree and the presence of fruit, the larval food source. Diapausing overwintering larvae require cold exposure (chilling) to terminate diapause in late winter or early spring. At the lower elevations close to the Columbia River the codling moth is bivoltine but gradually becomes univoltine at the higher elevations where the growing season is shorter and fewer heat units (above 10oC) are available for development. Long-term temperature records from the lower Hood River Valley indicate that the 25 years since 1985 have been considerable warmer than the 25 years prior to 1985. For instance, the average heat units available for codling moth development over a season have increased by more than 10% over the last 25 years. The codling moth is adapting to this warming trend by gradually increasing its voltinism (number of generations). As a result, the severity of codling moth as a pest can be expected to increase. Therefore, fruit growers will have to adjust and intensify control practices to keep fruit free from codling moth damage. We will also explore how other fruit and foliage feeding pests which are part of the pest complex of pears and apples in northern Oregon fare under different global warming scenarios compared to codling moth.

Deraeocoris brevis Knight (Hemiptera: Miridae) is a generalist predator and is a key natural enemy in pear orchards in the northwestern United States. Although D. brevis undoubtedly contributes to the regulation of major pear pests, pesticides often disrupt its activity and reduce its effectiveness as a biological control agent. A temperature-dependent stage-structured matrix model was developed to analyse the population dynamics of D. brevis influenced by insecticides. In this study, impacts of acetamiprid on field populations of D. brevis were analysed. The age class of D. brevis was categorized into four stages: eggs, small nymphs (1st to 3rd instar), large nymphs (4th to 5th instar), and adults. Probabilities for each element in the projection matrix were estimated using published temperature-dependent developmental data of D. brevis. Transition probabilities from an age class to the next age class or the probabilities of remaining in the age class were obtained from development rate function of each stage (age classes). The fecundity coefficients of adult population were the products of adult longevity completion rate (1/longevity) and temperature-dependent total fecundity. Also, direct and indirect residual effects of acetamiprid were incorporated into the model. The model results were much overestimated compared with observed actual data from 25d after model running. Such a discrepancy might be occurred from various reasons such as an intra-species competition, successful fecundity rate, etc. Further, the improvement and application of the model were discussed.