Species-specific differences in oak foliage affect preference and performance of gypsy moth caterpillars

The gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), is an introduced defoliator that preferentially feeds on oaks, Quercus spp. (Fagaceae) in the north-eastern USA. As the gypsy moth expands its geographic range, the extensive oak component in forests and urban environments of the USA assure its successful establishment. Given their economic and ecological importance, and the gypsy moth's potential to cause mortality, we evaluated caterpillar preference and performance on various oaks prevalent in the central hardwoods region. Most of the physical and chemical characteristics we measured, from budbreak phenology to foliar chemistry, varied significantly among the oak species tested. Similarly, insect preference and performance varied significantly, though not always in predictable ways. Caterpillar preference was compared for black, Q. velutina Lamarck, burr, Q. macrocarpa Michaux, cherrybark, Q. pagoda Rafinesque, northern red, Q. rubra L., pin, Q. palustris Muenchhausen, swamp white, Q. bicolor Willdenow, white, Q. alba L., and willow, Q. phellos L., oaks. Gypsy moth preference was greatest for black and burr, and least for northern red, pin, and willow oaks. We assessed foliar characteristics and caterpillar performance on foliage from burr, cherrybark, northern red, pin, and willow oaks. Caterpillar preference did not always correlate with performance. Gypsy moth consumption and growth were highest, and development most rapid, on pin oak, which had high nitrogen and tannin levels, and was among the least preferred. Northern red and willow oaks were also among the least preferred and were the least suitable tested, producing caterpillars with moderate to low consumption and growth rates, as well as the longest development. Northern red oak contained the lowest foliar tannins; willow oak foliage was lowest in carbohydrates and nitrogen. Our results suggest that a combination of foliar characteristics may be responsible for gypsy moth preference and performance, and that an optimal combination of foliar components serves to maximize host suitability. These data will provide information useful for planning and managing urban forests in the presence of expanding gypsy moth populations.