Breeding matters: Natal experience influences population state-dependent host acceptance by an eruptive insect herbivore

Abstract

Eruptive forest insects are highly influential agents of change in forest ecosystems, and their effects have increased with recent climate change. State-dependent life histories contribute significantly to the population dynamics of eruptive forest insect herbivores; however, the proximate mechanisms by which these species shift between states is poorly understood. Laboratory bioassays were conducted using the mountain pine beetle (Dendroctonus ponderosae) to determine the effect of maternal host selection on offspring host preferences, as they apply to population state-dependent behaviors. Female mountain pine beetles exhibited state-dependent preference for artificial host material amended with monoterpenes in the absence of other cues, such that individuals reared in high-density epidemic-state simulations rejected low monoterpene conditions, while low-density endemic-state beetles accepted low monoterpene conditions. State-specific behavior in offspring was dependent on rearing conditions, as a function of maternal host selection, and these effects were observed within one generation. Density-dependent host selection behaviors exhibited by female mountain pine beetle offspring is reinforced by context-dependent maternal effects arising from parental host selection, and in situ exposure to conspecifics. These results demonstrate potential proximate mechanisms that control population dynamics in eruptive forest insects, and will allow for more accurate predictions of continued impact and spread of these species.

Fig 1

A photo of an arena and technical drawings of the setup of the assay used to determine the effect of population state on substrate acceptance by female mountain pine beetles; a) image of “half-moon” configuration of artificial diet in petri dish, with an excavating mountain pine beetle, b) configuration of arena, light, and camera for recording beetle activity, c) configuration of arenas and light during assay. Drawings are not set to scale.

Fig 2. Mean (±SE) acceptance ratio (accept/reject) per trial (38 trials, 292 total beetles) of simulated phloem amended with three monoterpene concentrations by female mountain pine beetles reared in two population-density simulations over the course of 8-hour trials.

Fig 3. Mean (±SE) acceptance ratio (accept/reject) per trial (38 trials, 292 total beetles) of simulated phloem amended with three monoterpene concentration treatments by female mountain pine beetles, reared in two population-density simulations over the course of 8-hour trials.

Asterisks (*) indicate significant differences (p<0.05) determined by analysis of variance.