Comparing larval plum curculio, Conotrachelus nenuphar, emergence phenology in cherries and apples with implications for managing the pest in soil

Increasing legal restrictions on chemical pesticide use in stone and pome fruit orchards has stimulated efforts to develop residue-free fungi or nematodes as agents for control of the northern strain of the plum curculio, Conotrachelus nenuphar (Herbst).  When applied to soil to control this pest, the effectiveness of these agents declines rapidly.  To reduce agent wastage, novel and precise phenological models of plum curculio activity were developed to optimize the timing of agent application.  Larval development in Honeycrisp, Liberty and wild apples was observed in laboratory conditions while larval development in Montmorency tart cherries was recorded on trees in four orchards in springtime.  Median development time from egg until larval emergence from apples ranged from 207 to 336 degree days (base 10°C), with no difference in timing between larvae reared on Honeycrisp or on wild apples.  Median development time from egg until larval emergence from cherries ranged from 213 to 262 degree days.  Many more larvae emerged from large apples than from cherries and this result has implications for pest management.  An additional discovery was that when isolated with a single fruit, females frequently did not oviposit on the fruit.  When provided with multiple fruit, the recorded frequency of oviposition increased, suggesting that female roaming is an important aspect of oviposition behavior.  Also, field observations of plum curculio activity suggest that effective use of the developed phenological model in pest control strategies will depend upon precisely determining the timing of oviposition.