Comparing the emergence of northern strain plum Curculio larvae from multiple fruit varieties

Increasing restrictions on chemical pesticide use in orchards have encouraged the use of alternative strategies to control the northern strain of the plum curculio, Conotrachelus nenuphar (Herbst). Some of these strategies target larvae as they emerge from fruit, so existing models for larval emergence from fruit were evaluated for accuracy while examining the effect of multiple larvae and fruit type on emergence timing. Larval head width growth rate was established and used to gauge larval development. Larval emergence timing, quantified as degree-days (base 11.1 degrees C), was recorded in tart cherries on trees, and emergence timing was recorded in multiple apple varieties both in cyclical field conditions and in constant laboratory conditions. Ovipositing females and fruit were isolated, so larvae in a fruit were all siblings. Adult emergences from pupation in soil were recorded in the laboratory and compared with existing model predictions. Model predictions did not accurately reflect the timing of larval or adult emergence, and future incorporation of factors that could improve models are discussed. Colder conditions and changing host fruit type had no significant effect on larval emergence timing but changing host fruit type correlated with a shorter pupation interval. Results suggested that females preferred to oviposit on multiple fruit rather than lay multiple eggs in one fruit. Higher numbers of larvae per fruit did not significantly alter the timing of first larval emergence, although more larvae per fruit resulted in a significantly longer emergence period in apples.