POPULATION TRENDS OF FINNISH LEPIDOPTERA DURING 1961-1996

Based on a query and on a literature review, the population trends of Finnish Lepidoptera since Kaisila's (1962) thorough overview are analy sed. Changes in the belt of three coastal biogeographical provinces (V -EK) show significant correlations with those in three inland province s (St-ES). Furthermore, positive trends in these belts are reflected a s new provincial finds north of them. The spatial synchrony is suppose dly caused by spatially correlated climatic conditions. This is suppor ted by evidence of synchronous trends in species grouped according to their overwintering stages (Marttila 1991, Bruun 1992). The increased migration rate, indicated by the new provincial finds, is probably a c onsequence of high population densities, and does not explain the sync hrony itself. Kaisila's division into expansive and fluctuant species is considered to be a historical rather than a biological characteriza tion. During the 19th century, the reporting of new lepidopteran speci es was delayed by about 50 years if they were night-active vs. day-act ive. The low numbers of observers and slow development of collecting m ethods have caused further analytical uncertainties. Some of Kaisila's expansive species may actually have been inhabitants of Finland for l ong periods of time. At present, drainage of peatlands and overgrowth of meadows are the most adverse environmental changes causing a declin e of lepidopterans, particularly of the butterflies. Increase of bushi ness and reeds appear to have positively affected many geometrid and n octuid species. The high incidence of new provincial finds and of spec ies new to the country in the 1990s as well as positive trends in late -autumn and early-spring species supposedly reflect the ongoing climat ic change. The Finnish lepidopteran fauna is undergoing a dynamic phas e: around 30 recent invaders and 40 older expansive species are spread ing, while fewer are retreating; the declining species are mainly habi tat specialists while the expansive ones are generalists, mainly feedi ng on bushes and trees. Fewer expansions are evident among micro-than macrolepidopterans.