Benefits of Prolonged Male Residence with Mates and Brood in Pine Engravers (Coleoptera: Scolytidae)

In the pine engraver bark beetle, Ips pini (Coleoptera: Scolytidae), males stay in their breeding galleries for almost as long as their mates do - a period of several weeks. We examined several potential benefits of such a prolonged association of males with their mates in field studies. Attraction of additional females to male breeding sites and mate-guarding of current mates did not explain the observed male residence times, because the probability of arriving pine engravers of either sex was negligible within a week. Instead, a male-removal experiment showed that males significantly increased the reproductive rate of their mates, apparently by removing female-produced frass from the galleries, and males also defended the egg galleries against predators. Consequently, reproductive success tended to be greater when males were present. The breeding biology of bark beetles predisposes males to providing these types of assist