The plum curculio, Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae), is a common beetle endemic and native to the eastern United States. Native hosts include hawthorn trees, crabapple trees, and the Chickasaw plum. After the introduction of domesticated fruit trees, the plum curculio began using crop trees as hosts. Now, its pest status well established, the plum curculio is a problem in commercial fruit production for a number of trees in the Rosaceae family—including plums, peaches, and apples. Accordingly, “it is the considered opinion of entomologists that plum curculios, not gravity, cause apples to fall” (Berenbaum 1991). In the eastern United States, plum curculio is an obstacle to organic and low-spray commercial fruit growing operations. Alternative control measures under development include nematode biocontrol and pheromone traps.
Adult female plum curculio oviposit in the immature fruit, leaving a telltale crescent-shaped scar. The tiny larvae burrow into the seed cavity where they spend several weeks maturing. Infected fruit drops from the tree prematurely and the grub emerges from the fallen fruit to excavate a small cavity in the soil. There it pupates and the adult weevil emerges a month or more later. In the North, these adults represent the only generation each year and they spend the rest of the season feeding on fruit and foliage in anticipation of overwintering. Southern plum curculio will go through another generation, possible more. The limits of the weevil’s distribution extend as far west as the 105th meridian, though records west of the 97th meridian are rare. The northern extent reaches into Canada and the southern extent falls just short of the Gulf coast.
There are two known, overlapping strains of the plum curculio. The northern strain preferentially feeds and oviposits on apple (Malus spp.) and is univoltine. The southern strain favors peaches (Prunus spp.) and is multivoltine. The transition zone is thought to run roughly along the 39th parallel (Chapman, 1938).