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-feedi ng, and sucking) and leaf characteristics (toughness as measured by re sistance to penetration, and specific leaf area) were examined during 2 summers along a climatic and Vegetation gradient in the southwest Un ited States. Strip-feeding insects were more abundant, and needles wer e softer (less resistant to penetration) and thinner (higher specific leaf area) on pinon pines of summer-wet southeast Arizona than on pino n pines of the drier summer climates of northcentral and northwest Ari zona. Sucking insects were more abundant and needles were tougher on p inon pines of northcentral Arizona. Pit-feeding insects were less abun dant on southeast pinon pines (the difference was significant in 1990 but not 1991) and showed different abundance on northcentral and north west pinon pines between the 2 summers.