Preemergence mating, inbreeding, and their consequences in the bark beetle Ips typographus

Scolytinae is a subfamily of weevils that contains many major pest species. Most scolytines employ an outbreeding mating system: individuals emerge from their natal host trees and fly to new hosts, where they mate with unrelated conspecifics. However, in several outbreeding species, some individuals mate prior to emergence, either with a sibling or an unrelated neighbor from another gallery. Preemergence mating allows females to start adult life with a supply of sperm; they can then dig a gallery on their own in a new host tree. In this study, we examined preemergence mating in Ips typographus, a supposedly outbred bark beetle that causes considerable damage to European spruce forests. Our field and laboratory studies have shown that 15-94% of females are mated at (re)emergence, a wide range of values that is shaped by environmental conditions and time of year. This figure is also positively correlated with time spent under the bark. Moreover, in laboratory experiments, outbreeding females had the same level of productivity whether they established themselves with a partner or on their own. However, compared to both types of outbreeding females, solitary inbreeding females exhibited lower productivity due to higher mortality in the egg and postlarval stages, suggesting the presence of inbreeding depression. In a choice experiment, females preferentially entered nuptial chambers containing unrelated males versus brothers. These results shed new light on this bark beetle's mating behavior, which ultimately influences the species' ability to colonize new areas.

Automated summary

This study examined preemergence mating in Ips typographus, a supposedly outbred bark beetle. The results showed that 15-94% of females engage in mating at (re)emergence, with the proportion influenced by environmental conditions and time. Our findings also revealed that outbreeding females had the same level of productivity whether they established with a partner or on their own, while inbreeding females exhibited lower productivity due to higher mortality rates. In addition, females showed a preference for nuptial chambers containing unrelated males over brothers.