Investigating the factors influencing trap capture of bark and ambrosia beetles using long-term trapping data in a cool temperate forest in central Japan

Abstract

ABSTRACT From 1994 to 2003, bark and ambrosia beetles were captured from April to November at 12 sites in the University of Tokyo Chichibu Forest, central Japan, using flight-barrier traps with alpha-pinene and ethanol as a lure. Additional trapping was conducted between July 2013 and November 2014 at the same sites using Lindgren’s funnel traps with ethanol. Factors influencing trap captures were investigated, accounting especially for the indirect influence of sika deer on beetle populations due to induced tree mortality. Owing to incomplete data collection in 2013, trap captures of August and after August (“AUG” for 12 years) were analyzed separately from those of the whole season (“ALL” for 11 years). Trap captures in 2013–2014 were greater than those in 1994–2003. There was also an increase in the number of species across both periods, which was more conspicuous in “AUG”. Seventeen indicator species were found in 2013–2014, and only two in 1994–2003. This could be partially explained by the difference in the lure used. A sudden population increase in 25 species was observed between the average over 1994–2003 and 2013–2014. Increasing trends during the 1994–2003 were also recognized in 13 species, with a sudden increase in 6 species in the last few years of the period. These coincided with increases in sika deer populations across both periods. An increase in tree mortality caused by increases in the deer population is likely the cause of the increase in bark and ambrosia beetles.