Assessment of pine weevil numbers on clear-cut and forest sites with shelter boards and pitfall traps

Field experiments were conducted in 1991 and 1992 on clear-cut and forest sites in four forest areas in southern Sweden with the aim to test possibilities for estimating pine weevil (Coleoptera: Curculionidae) population sizes. More pine weevils (Hylobius abietis andH. pinastri) were caught in baited pitfall traps than under shelter boards. The proportions ofH. pinastri in the totalHylobius catch were higher under shelter boards than in pitfall traps, indicating a difference between the species in behaviour towards the trap types. Numbers ofH. abietis found on forest sites were lower than those on fresh clear-cut sites, but not those on one year old or older clear cut sites. In mark-recapture experiments the recapture rates ofH. abietis ranged from zero to 73%; they were zero on fresh clear-cut sites. Recapture rate was not correlated to dispersal distance. Estimates of population size (Schnabel method) were in magnitudes of 150 to 5000H. abietis per hectare. The estimates did not reveal consistent differences between forest and one-year old or older clear cuttings. Dispersal distances were on average 6.0 m in 1991 and 5.4 m in 1992. Only in one area in 1992 the dispersal distances were significantly different between forest and clear-cut site.