Monogamy in the bark beetle Ips latidens: ecological correlates of an unusual mating system

Abstract

Abstract. 1. The diversity of mating systems in bark beetles (Coleoptera: Scolytidae) is poorly understood. Ips latidens (LeConte) is a small‐bodied species of a harem polygynous genus whose mating system in nature had not been established previously. This study examines the breeding biology of I. latidens breeding in recently dead ponderosa pine (Pinus ponderosa) in California. It was expected that both the heterogeneous habitat quality inherent in dead trees and small body size would favour polygyny.2. Contrary to expectations, I. latidens was found to be monogamous on the basis of excavations of 131 galleries conducted throughout the oviposition period at two wind‐felled trees and at four sites composed of freshly‐cut logs. Males left the galleries much sooner than females (50% gone by 24 and 36 days, respectively).3. Individual females made up to four egg gallery arms extending from the male nuptial chamber, with the number of arms and the length of individual arms increasing with the age of the gallery. The relationship between total gallery length and gallery age was consistent among the trees and log sites, and did not depend on the presence of the male.4. Ips latidens bred in a wide range of tree diameters (10–24 cm), and occurred in both pure aggregations and in aggregations with two other bark beetle species, Dendroctonus brevicomis and I. paraconfusus. The presence of the other species did not appear to influence negatively the density of I. latidens.5. Monogamy in I. latidens may be due to lower male mortality during dispersal associated with a greater range of suitable breeding habitat than occurs for other Ips species, resulting in an even sex ratio at breeding sites.