Phytophagous insect complex associated with cones of white fir, Abies concolor (Gord. and Glend.) Lindl., and its impact on seed production.
White fir (Abies concolor) cones were sampled for insect damage from wild stands in California and Nevada during 1984-86. Insects were recovered from cones and seed damage was partitioned by insect species. The important phytophagous insects were separated into guilds: the cone- and seed-mining guild, Dioryctria abietivorella, Eucosma (probably E. siskiyouana), Cydia (probably C. bracteatana), and Barbara sp.; the seed-feeding guild, Megastigmus pinus, M. rafni, Earomyia abietum; and the scale- and bract-feeding guild, Asynapta hopkinsi, Dasineura (probably D. abiesemia), Resseliella conicola and Strobilomyia abietis. Total damage by insects varied by year and site, reaching a maximum of 47% in 1986 on one site and a minimum of 12.5% in 1984 on another. Abortion and incomplete development were also major factors in the production of sound seed. Populations of white fir cone and seed insects varied with cone crop but were also affected by the occurrence of cone crops on alternative hosts. During most years, the seed-mining guild insects were the major cause of seed damage.