OCCURRENCE AND DYNAMICS OF NOSEMA-MELIGETHI (MICROSPORIDA) IN POPULATIONS OF MELIGETHES-AENEUS (COLEOPTERA, NITIDULIDAE) IN FINLAND

A total of 221 samples of the beetle Meligethes aeneus Fabricius were collected from southern and central Finland in 1989-90, and 10 152 bee tles were individually examined to determine the occurrence of the mic rosporidian disease Nosema meligethi Issi & Raditsheva. The dynamics o f this disease was followed at seven sites throughout the season, and its ecological aspects were studied at one locality, Hartola. The leve l of N. meligethi infection steadily increased in M. aeneus population s during the season, with horizontal transmission appearing to take pl ace in flowerheads, where the beetles aggregate to feed. Infected beet les migrated to overwintering sites earlier than did healthy beetles, and just prior to overwintering, infected beetles were lighter in weig ht than healthy ones. This fact may drastically affect the overwinteri ng survival of infected beetles.