d'Eustachio, Gabriel JohnLandscape managers need durable, effective, and safe methods for controlling key pests of valued plants in both landscape and nursery settings. The boxwood leafminer (Monarthropalpus flavus, Diptera: Cecidomyiidae) is a serious pest of boxwoods. Boxwoods (Buxus sp.) are a key plant in suburban Maryland landscapes. They are the second most common woody ornamental plant in these settings. In a recent study almost 43% of boxwoods surveyed required treatment for leafminer infestation. Boxwood leafminers also pose a serious problem in historical gardens, such as Longwood Gardens, PA, Dumbarton Oaks and the US National Arboretum in Washington, DC. At the present time, there is a lack of a comprehensive, environmentally sound, management program for the boxwood leafminer. The first step toward an effective management strategy is a better understanding of the boxwood leafminer's life cycle. Over the summers of 1994-1995, leafminer populations were surveyed and life cycles documented and correlated with growing degree days. The first growing degree day developmental chart for boxwood leafminer was developed. Various pesticides were tested in 1995. Different chemicals and application times were evaluated for control of both adults and larvae. At present it appears that application of a translaminar pesticide such as Avid or Merit at adult emergence (growing degree day 352) provides the best control. Resistant cultivars appear to be the most durable, simplest method to control the leafminer. Some cultivars.are highly resistant to boxwood leafminer attack while others are highly susceptible. The third goal of my project was to identify resistant cultivars. This was accomplished by first observing natural variation in leafminer populations in the field. Next I caged ovipositing adults on terminal branches of various cultivars of boxwood, and measured survival of larvae. All cultivars received heavy oviposition with equal frequency, although survival rates were very different. Finally, I tested the hypothesis that leafminers could discriminate among resistant and susceptible cultivars. To test this emerging adults were caged with different cultivars of boxwood and allowed to select plants for oviposition. Plants were then analyzed to determine acceptance of various host plants. I found that although survival on different cultivars can vary dramatically, leafminers were unable to distinguish between suitable and unsuitable host plants.enThesis