ENVIRONMENTAL AND CLONAL INFLUENCES ON HOST CHOICE AND LARVAL SURVIVAL IN A LEAFMINING INSECT

1. The larvae of Phytomyza ilicicola (native holly leafminer) generall y have higher survivorship and densities on Ilex opaca (American holly ) grown in cultured suburban settings than on natural forest trees. 2. Survival and density also vary among trees within these two habitats; natural enemies and host-plant factors are thought to generate betwee n-habitat variation in Phytomyza densities, while mainly host factors generate within-habitat variation. 3. We explored the latter by examin ing the effects of fertilization, clonal variation, exposure to sunlig ht and site of exposure to attack (forest or open field) on Phytomyza success using potted holly clones in a common garden setting. 4. Ferti lization, clonal variation and site of exposure to attack all influenc ed various measures of Phytomyza success whereas exposure to sunlight did not.5. Fertilized plants had 32% more adult feeding, 47% more ovip ositions (as determined by the number of first instar larvae), 9.5% gr eater larval survival and 7% heavier pupae than did unfertilized plant s. 6. Clonal variation had no influence on adult leafminer feeding, bu t influenced both oviposition (29% lower on clone 30 than on clones 65 and A1) and larval survival (over 60% higher on clone 65 than on clon es A1 and 30). 7. Plants that were exposed to leafminer attack in a su nny open field had 50% more feeding scars and 82% more first instar la rvae than did those exposed in a shaded woodlot. There were no differe nces in larval survival between the two sites. 8. Density variation is influenced by adult discrimination among trees by adult leafminers in feeding and oviposition, and by differential mortality and growth of the larvae after oviposition.