THE RELATIONSHIP BETWEEN ABUNDANCE AND PERFORMANCE OF ERIOCRANIA MINERS IN THE FIELD - EFFECTS OF THE SCALE AND LARVAL TRAITS STUDIED

1. This paper examines patterns of host use and larval performance in solitary and gregarious birch-feeding Eriocrania miners. We compared t he correspondence between miner abundance and different components of larval performance at various scales (sites, birch species, individual trees). 2. Infestation levels, larval mass, survival, mortality from different causes and feeding efficiency of Eriocrania miners varied at all scales. 3. We found a correspondence between patterns of host use and larval performance in birch leaf-miners only at some scales: at t he level of the birch species in the gregarious E. haworthi Bradley an d at the level of the individual tree in the complex of solitary speci es. 4. The parameters of larval performance were in general poorly cor related with each other. The probability of larval survival seemed to be the critical factor for solitary Eriocrania miners, whereas for E. haworthi plant quality was more important. 5. Although some correlatio ns between patterns of host use and larval performance of Eriocrania m iners were statistically significant, larval performance explained les s than 10% of the variation in miner density at any level. 6. We assum e that a good correspondence between patterns of host use and larval p erformance is rarely observed in the field because the distribution of larvae among and within patches is affected by numerous factors besid es oviposition preference and offspring performance.