Effect of Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) Larval Population Levels onPopulusTerminal Damage

Abstract

The cottonwood leaf beetle, Chrysomela scripta F., is a major defoliating pest of Populus in North America. We determined the relationship between larval population densities and defoliation levels in central Iowa, and related that to potential biomass loss. During the 1995 and 1996 growing seasons, egg mass surveys were performed: in 1995 for generation 2 and in 1996 for all 3 generations. Open and caged Populus trees were infested with different populations of freshly eclosed larvae on actively growing terminals. The 1996 observations from the open and caged trees in the 2nd generation and from the caged trees in generations 1 and 3 are consistent with those of the open and caged trees of the 1995 2nd generation. The results from the open trees during the 1st and 3rd generations in 1996 are much different from those of the 2nd generation in either year. The probability of reaching damage levels that cause biomass loss is greatest for the 2nd generation. Egg mass density may be useful in predicting damage levels. Damage rating is an accurate estimator of foliage loss.