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 beetles were individually examined to determine the occurrence of the microsporidian disease Nosema meligethi Issi & Raditsheva. The dynamics of this disease was followed at seven sites throughout the season, and its ecological aspects were studied at one locality, Hartola. The level of N. meligethi infection steadily increased in M. aeneus populations during the season, with horizontal transmission appearing to take place in flowerheads, where the beetles aggregate to feed. Infected beetles migrated to overwintering sites earlier than did healthy beetles, and just prior to overwintering, infected beetles were lighter in weight than healthy ones. This fact may drastically affect the overwintering survival of infected beetles.