ABSTRACT

Parental care and colonial breeding are both widespread in two related groups of weevils known traditionally as Scolytidae and Platypodidae. Within–family cooperative breeding and eusociality also occur; in at least one platypodid ambrosia beetle, non–reproductive females help presumed relatives to raise offspring.

Although they breed in a wide variety of woody tissues, the majority of species fall into two ecological categories, those reproducing under the bark and feeding directly on inner bark (‘bark beetles’, most scolytids) and diverse taxa feeding upon microbial ectosymbionts they have introduced to the walls of their tunnel systems (‘ambrosia beetles’, many scolytids and all true platypodids). In both scolytids and platypodids, females lay eggs over an extended period of time in long tunnels. Males usually remain with females in these tunnel systems, controlling and expelling refuse. We examine hypotheses for prolonged male residence, and find that the most likely explanations for long stays in burrows are either blocking out natural enemies or increasing the reproductive rate of the resident females.

Species reproducing in bark or wood usually breed in large aggregations. In most species, these colonies are an incidental effect of mutual attraction to odors emanating either from the resource itself or from the beetles (pheromones). We suggest that the key feature predisposing these beetles to the evolution of breeding in aggregations is the presence of mate–attracting pheromones coupled with the utilization of resource patches that cannot be monopolized by single families.