Negative effects of free-living nematodes on the populations of Bursaphelenchus xylophilus in dead pine trees

Abstract

The pine wood nematode (PWN), Bursaphelenchus xylophilus Nickle, is a devastating pathogen of pine forests that has caused significant economic losses and ecological damage in East Asia and Europe. Efficient and environmentally friendly methods for controlling the PWN are limited, and it is therefore necessary to explore alternative management methods. Competition between nematode populations inhibits the growth and development of one competing population. Free-living nematodes (FLNs), which are scavengers, are reported to have biological control potential and may have important value in controlling the PWN. We created a new medium that allows the rapid production of FLNs isolated from dead pine trees and studied interspecies competition. Single-factor and orthogonal tests were utilized to screen the main components of the medium and optimize ratios, respectively. Five species of FLNs were cultured in large numbers in the optimized medium. Quantified FLN/PWN competition was quantified in the laboratory, and its impact was assessed in the field with two inoculation methods. The main components of the medium are pine sawdust, glucose and agar, and the optimal ratio is 30 g/L pine sawdust, 10–20 g/L glucose and 30 g/L agar. Of the five nematode species, JR-3 (Parasitorhabditis sp.) significantly reduced PWN population densities in both the laboratory and field. The PWN population density in the wood samples around the pupal chamber was 2.91 in the experimental group compared to 13.64 in the control group during the same period in the field. This is the first study on interspecies competition between FLNs and the PWN in dead trees. JR-3 increased the rate of PWN population eradication and has the potential to help control pine wilt disease.