The evolution of mating systems in bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae)

Abstract

The extraordinary array of mating systems in the Scolytidae and Platypodidae has been largely overlookrd by resrarchers interested in the evolution ofsexual behaviour. This paper proipides the first overview of reproducti\ e behaviour in this important and widespread group, known to most biologists only by the reputations of tree-killing taxa.Referred to generally as 'bark beetles', these insects chew egg tunnels inside a variety of (usually deadi plant tissues, though most species are either phloeophagous (breeding in the inner bark ofwoody p h t S J or xylomycetophagoris (all stages feeding on mutualistic fungi growing on sapwood or heartwood). In most species, permanent records of many aspects of reproductive behaviour are etched in the host; in many, engra\ings reveal female fecundity, eggs sired per male, hatching success, and offspring survivorship. Each gallery arm represents a good portion of a given female's lifetime reproduction. but in many species females commonly reemerge to reproduce in one or two additional sites.In most species of bark beetles, each female initiates her own gallery, to be joined later by a male. These monogynous gallery systems are associated with mating systems defined by how long males stay with females: in a few species, males seldom ife\,erjoin females under the bark; in the vast majority of species, males stay for part or all of the oviposition period then leave to seek other mates; and a few groups exhibit permanent monogamy, in that both sexes die in their only gallery system. \VliiIc these patterns emerge from an overview of the world scolytid fauna, the length ofmale residency has seldom been quantified, and the costs arid benefits associated with male mating strategies have not been measured for any bark beetle.Male-initiated monogyny is uncommon in Scolytidae, though the rule in Platypodidae; all instances of which I am aware are summarized from a phylogenetic perspective.Inbreeding polygyny with highly biased sex ratios has arisen at least seven times in Scolytidae. These taxa are usually characterized by males being dwarfed, flightless, and uncommon. Sex determination is known for only a few examples, hut both haplodiploidy and diplodiploidv have been reported.Multiple origins of harem poly~qny (otherwise rare in invertebrates] add an exciting dimension to the comparative and experimental study ofscolytid mating systems. In harem polygynous taxa, males initiate gallery construction. I summarize what little can be learned from the literature about the fine structiire of harem polygynous mating systems in bark beetles, and the problem of measuring reproducti1.e success. Data on the nature of harem polygyny in Pityophthorus lautus are presented, illustrating ( a , the fluidity ofharems; (b) that average eggs laid per gallery arm is relatively unaffected by harem size, but strongly influenced by resource quality; (cl that male egg-gain is strongly correlated with territory quality (a consequence of (b) above); and (di the temporal patterning of immigration and emigration ...

Evidence of Xyleborinus attenuatus (Blandford 1894) (Coleoptera: Curculionidae: Scolytinae: Xyleborini) populations in Quebec, Canada

“…Moreover, xyleborine ambrosia beetles are the perfect candidates for the invasion of new habitats because of their large host plant spectrum and their ability to inbreed. Theoretically, a single fertilized female can potentially start an entirely new population (Kirkendall 1983;Jordal et al 2001). In conclusion, X. attenuatus has recently arrived in Quebec and continues to spread over the province's territory.…”

Community structure and reproductive biology of bark beetles (Coleoptera: Scolytinae) associated with Macaronesian Euphorbia shrubs

“…The considerable variation in time that a male spends together with the egg laying female is also noteworthy, insofar as very few insects show this kind of variation within a species (Kirkendall, 1983). Although only A. jubae provided enough data to infer intraspecific variation, the large variation also between close relatives further indicate that this could also apply to other Aphanarthrum species.…”

“…Promiscuous mating is quite likely under such circumstances, rendering both sexes polygamous. The communal behaviour is rare among most bark beetles, but was previously reported for another crypturgine beetle, Crypturgus pusillus, which breed in conifers (see Kirkendall, 1983). Interestingly, species of the basal crypturgine genus Dolurgus and Crypturgus, are frequently found using the entrance hole of a larger, established species (Schwarz, 1894;Wood, 1982;pers.…”

Effects of ingredients and structure of semi-artificial diet on the reproduction of an ambrosia beetle, Xyleborus pfeili (Ratzeburg) (Coleoptera: Curculionidae: Scolytinae)

“…The tribe Xyleborini, which includes the genus Xyleborus, has an inbred polygynous mating system in which female adults mate with their male siblings in their galleries before dispersal flight (e.g., Kirkendall, 1983).…”