Assessment of three techniques for measuring natural enemy inflicted mortality of leafroller larvae in commercial orchards

Measuring natural enemy (NE) inflicted mortality presents a serious challenge in managed habitats, such as apple orchards, where the crop-plant is frequently treated with a wide range of insecticides. Toxic residues keep natural populations of pests at too low levels to sample and prevent the use of techniques in which laboratory reared insects are released directly on foliage and used to measure NE activity. Three methods to implant obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) larvae were tested: (1) larvae placed on potted apple trees, (2) larvae placed on excised leaves inserted in florists' waterpicks and (3) larvae placed on branches placed into water filled Polyvinyl chloride (PVC) pipes. Use of potted trees allowed accurate estimation of NE inflicted mortality; however, this method was very labor intensive. The waterpick method required less labor, but it underestimated larval mortality caused by NEs. The use of PVC pipes to hold infested branches combined the benefits of the other two methods tested. This technique was simple to use and provided accurate estimates of NE inflicted mortality.