Relationships between the fecundity of two bark beetle pests and the presence of antagonist

Although previous research has documented the occurrence of antagonists of bark beetles, the studies have only evaluated individual antagonists and have not assessed the overall effect of all antagonists on adult beetles. In this study, we determined which antagonists were associated with reduction in the fecundity and maternal gallery lengths of two important species of bark beetles: Ips typographus on spruce and I. cembrae on larch. We evaluated these relationships under natural conditions by collecting maternal females in galleries and dissecting and examining their internal organs. The antagonists in the I. typographus hemolymph had the most significant negative associations with fecundity and gallery length. These antagonists were mainly nematodes and parasitoids in the hemocoel. In contrast, a positive association was found between gregarine presence and I. typographus fecundity. No antagonist was found that was likely to significantly alter I. cembrae fecundity or maternal gallery length. Our study provides the first comprehensive assessment of antagonists that may have the potential to reduce the fecundity and thereby reduce the outbreaks of these bark beetles.