ADULT FEEDING AND OVIPOSITION OF PHYTOMYZA-ILICICOLA (DIPTERA, AGROMYZIDAE) IN RESPONSE TO LEAF AND TREE PHENOLOGY

The influence of leaf phenology on host discrimination by Phytomyza il icicola Loew was explored in the laboratory by examining the influence s of leaf age-shoot position on adult feeding and oviposition and leaf age only (independent of relative leaf position on expanding shoots) on adult feeding. The relationship between adult feeding and shoot phe nology among trees was also examined in 10 American hollies, Ilex opac a Aiton, growing under natural forested conditions. Three age-position classes of leaves were recognized on new growth in the spring: young folded leaves at shoot tips, expanding leaves at midshoot, and fully e xpanded hardening leaves at the base of shoots. For leaf age-position, feeding by adult P. ilicicola was similar on expanding leaves and ful ly expanded leaves and 3.6 times greater on shoot tip leaves than on e xpanding and fully expanded leaves. For leaf age independent of positi on, feeding by adult P. ilicicola was 9 times greater on expanding lea ves than on fully expanded leaves and 20.7 and 2.2 times greater, resp ectively, on shoot tip leaves than on fully expanded leaves and expand ing leaves, Oviposition was independent of leaf age and position on ne w shoots. There was no relationship between tree phenology and intensi ty of feeding under natural conditions.