Temperature affects phenological synchrony in a tree-killing bark beetle

Abstract

Phenological synchrony can promote population growth in species with positive density dependence. Variation among life stages in the thermal thresholds for development can foster phenological synchrony under thermal regimes that include frequent occurrence of temperatures between developmental thresholds. The southern pine beetle is an insect with positive density dependence that has recently undergone important shifts in population abundance at the northern extremes of their distribution. We evaluated the hypothesis that cooler winter temperatures in their northern range cause a convergence of the population life stage structure that leads to synchrony in spring flight phenology. We used a combination of approaches. First, in situ laboratory experiments demonstrated a threshold temperature for pupation that was greater than was required for larval development; rearing larvae at lower temperatures increased the pooling of individuals at the end stage of larval development and synchrony in adult emergence. Second, a development rate model showed a similar convergence of the majority of the population at the end stage of larval development when brood experienced the cooler temperatures of the northern region, but not with temperatures from the southern region, or as a null model. Finally, field trapping of wild beetles showed greater synchrony in the pine forests of New Jersey than in the warmer, historically occupied forests of Georgia and Mississippi. Given these results, pine-dominated forests in the northern edge of the southern pine beetle's range may experience more frequent occurrence of outbreaks, due to the positive feedbacks associated with a synchronous spring emergence of this insect.

Evaluation of Phenological Indicators for Optimizing Spring Southern Pine Beetle (Coleoptera: Curculionidae: Scolytinae) Trapping Surveys

“…Adults may emerge and disperse after a few unseasonably warm d in the winter and early spring (Moser & Dell 1979). Cold winters should promote a synchronous spring emergence, particularly in the northern portion of the range of D. frontalis and higher elevation pine forests (Lombadero et al 2018). Warmer winters result in staggered emergence as was observed in our study in southern states.…”

Towards Sustainable Forest Management in Central America: Review of Southern Pine Beetle (Dendroctonus frontalis Zimmermann) Outbreaks, Their Causes, and Solutions

“…Another climate-related factor that distinguishes Central America from other regions is the effect of low temperatures. In the North, SPB range is limited by winter temperatures [15], which will not be the case anywhere south of Mexico.…”

“…The activity of SPB depends on two robust predictors: the availability of suitable host material (basal area), and predators and parasites, whose abundance may contribute to the outbreak dynamics [13,14]. Climatic parameters control SPB outbreaks on the edges of the insect's distribution [15]. The southern pine beetle is unique among bark beetles in that its outbreaks regularly occur in stands of healthy trees, rather than being dependent on poor stressed trees, as Ips and most other Dendroctonus spp.…”

The Southern Pine Beetle Dendroctonus frontalis (Coleoptera: Curculionidae: Scolytinae)

“…The most likely hypothesis for this distribution is the scarcity and/or lack of loblolly pine in the southern half of the state. In the northeastern United States, SPB has recently (since 2014) expanded into Connecticut, New York, and Rhode Island, as a result of warmer winter temperatures (Lombardo et al 2018).…”