Estimated life history of the curculionid needleminer <i>Parendaeus abietinus</i> in relation to defoliation damage in fir trees

The curculionid needleminer Parendaeus abietinus has caused severe defoliation and deaths of fir trees (Abies spp.) in Iwate prefecture. So far, its biology is unknown. We investigated its life history and how defoliation and tree death progressed with infestation by P. abietinus and secondary mortality agents, such as boring insects, to provide useful ideas for the future management of fir tree stands with a P. abietinus outbreak. Adults emerge from late June to early July, eggs are deposited on current year shoots, and larvae mine needles which drop from trees to the litter where they overwinter. Pupation started in June and lasted about 2 weeks. Dissection of dropped mined needles revealed that few parasitoids exploited them. Borers targeted wholly defoliated trees with reduced resin activity, although some trees died without secondary attack. This suggests that P. abietinus can kill trees alone. Adults fed on and oviposited on only current-year needles, defoliating 50% of them, but annual loss of 20% to 30% of 1- to 3-year-old needles also occurred. Although the mechanisms for the older-age needle loss are unknown, the annual loss suggests that needleminer infestation over 4 years or more can wholly defoliate fir trees, in which needle longevity is eight years. To reduce needleminer populations, litter could be removed in areas with high needleminer population densities.