Pattern of Herbivore Abundance Along a Climatic Gradient: Guild Shift of Leaf-Feeding Insects and Changes in Leaf Characteristics

The abundance of insects in 3 feeding guilds (strip-feeding, pit-feeding, and sucking) and leaf characteristics (toughness as measured by resistance to penetration, and specific leaf area) were examined during 2 summers along a climatic and vegetation gradient in the southwest United States. Strip-feeding insects were more abundant, and needles were softer (less resistant to penetration) and thinner (higher specific leaf area) on piñon pines of summer-wet southeast Arizona than on piñon pines of the drier summer climates of northcentral and northwest Arizona. Sucking insects were more abundant and needles were tougher on piñon pines of northcentral Arizona. Pit-feeding insects were less abundant on southeast piñon pines (the difference was significant in 1990 but not 1991) and showed different abundance on northcentral and northwest piñon pines between the 2 summers.