SPATIAL-DISTRIBUTION PATTERNS OF PINE SAWFLIES (HYMENOPTERA, DIPRIONIDAE) IN ARIZONA, US AND SICHUAN, PR OF CHINA

In a comparison study of sawfly distribution patterns in the western U S and southwestern China, we found that defoliation and oviposition we re limited to certain forest stand characteristics. Both species (Neod iprion autumnalis Smith in Arizona, US and N. xiangyunicus (Xiao and H uang) in Sichuan, P.R. China) were restricted to pure stands of their hosts at specific elevations. Defoliation of ponderosa pine (Pinus pon derosa Dougl. ex Law.) by N. autumnalis was limited to a narrow elevat ional band (2410-2440 m) within the range of its host at the study sit e (approximately 2350-2650 m). Defoliation of and oviposition on yunna n pine (P. yunnanensis Franch.) by N. xiangyunicus was confined to a s pecific but wider elevational band (1850-2050 m) within the host range of the area studied (1650-2050 m), The density of ponderosa pine tree s (measured as basal area (m(2) ha(-1))) also appears to play a role i n the distribution of N. autumnalis. Defoliation by this species was l imited to stand basal areas of less than 4.6 m(2) ha(-1). Stand densit y does not appear to have a significant influence on N. xiangyunicus d efoliation patterns, However, a significant interaction between stand density and Vertical crown position on oviposition by N. xiangyunicus was detected, Proportionately more egg clusters were found in the top of crowns at low stand densities, while egg clusters were located in t he middle and bottom of crowns equally at all stand densities. Signifi cant differences in defoliation intensity were not detected between cr own level for either species. In addition to discerning these distribu tion patterns, we established that foliage characteristics varied acro ss stand density and elevation gradients in both Arizona and Sichuan. Needles in low density compared with high density stands in Arizona we re longer, wider, tougher, and had less water. Pine needles in Sichuan followed this same general pattern when comparing the foliage from lo w elevations with foliage from high elevations. We propose that longer needles of open-grown trees in Arizona allow ovipositing females to l ay more eggs per needle which in turn benefits larval performance thro ugh increased feeding and defense against natural enemies. The 20% mor e tough needles of yunnan pine at low elevations in Sichuan may confin e oviposition and larval feeding to higher elevations.