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 pinon pines of summer-wet southeast Arizona than on pinon pines of the drier summer climates of northcentral and northwest Arizona. Sucking insects were more abundant and needles were tougher on pinon pines of northcentral Arizona. Pit-feeding insects were less abundant on southeast pinon pines (the difference was significant in 1990 but not 1991) and showed different abundance on northcentral and northwest pinon pines between the 2 summers.