Efficiency Enhancement Technology of Dastarcus helophoroides (Coleoptera: Bothrideridae) for Controlling Monochamus alternatus (Coleoptera: Cerambycidae): Drilling Optimization and Biological Collaboration

<i>Dastarcus helophoroides</i> Fairmaire, a parasitic natural enemy widely used in the biological control of <i>Monochamus alternatus</i> Hope, possesses strong abilities to search for hosts and prey. To enhance the biological control efficacy of <i>D. helophoroides</i> against <i>M. alternatus</i>, this study systematically evaluated the effectiveness of enhancing control through methods such as drilling holes in lure logs and introducing <i>D. helophoroides</i> carrying <i>Pyemotes zhonghuajia</i> or <i>Beauveria bassiana</i> under controlled indoor conditions. The results showed that: (1) Releasing <i>D. helophoroides</i> eggs (after 30 days) and releasing adults (after 120 days) were both effective in controlling <i>M. alternatus</i>, with the best control effects achieved when 50 eggs/m and 3 adults/m were released. The release of adults took longer to show effects but had better results than the release of eggs in the later stages. (2) The location and number of holes drilled in lure logs significantly influenced the efficiency of <i>D. helophoroides</i> in searching for and parasitizing <i>M. alternatus</i>, while the diameter of the holes was not significant. Considering the highest control efficacy and minimizing damage to the tree, the optimal conditions were releasing <i>D. helophoroides</i> adults 2 cm above <i>M. alternatus</i> fecal holes, with 0.4 cm in diameter and 2 holes/m release density, which significantly promoted the invasion of <i>D. helophoroides</i> adults into the borer tunnels and increased the <i>M. alternatus</i> mortality rate. (3) Releasing <i>D. helophoroides</i> adults carrying <i>P. zhonghuajia</i> or <i>B. bassiana</i> significantly improves the control efficacy against <i>M. alternatus</i>. The higher the number of <i>D. helophoroides</i> adults released per log segment and the greater the quantity of <i>P. zhonghuajia</i> or <i>B. bassiana</i> that they carry, the higher the mortality rate of <i>M. alternatus</i>. After 60 days of release, the highest mortality rate of <i>M. alternatus</i> was observed in treatments where <i>D. helophoroides</i> (released at densities of 3 adults per meter of log segment) carried <i>P. zhonghuajia</i> (0.6 million/m) or were sprayed with <i>B. bassiana</i> (3 g/m). The synergistic effect of carrying <i>P. zhonghuajia</i> was evident, but the overall control efficacy of spraying <i>B. bassiana</i> was limited. In summary, optimizing drilling techniques and combining biological release strategies under laboratory conditions can significantly enhance the control efficacy against <i>M. alternatus</i>, providing data support for <i>D. helophoroides</i> future application in forest pest control.