Morphological variation associated with dispersal capacity in a tree‐killing bark beetleDendroctonus ponderosaeHopkins

Abstract

1 Intrinsic factors influencing the dispersal of insect pests during outbreaks are poorly understood, yet these factors need to be quantified to parameterize dispersal in models that predict population spread. The present study related wing and body morphology of female mountain pine beetles (Dendroctonus ponderosae) to flight distance, as measured by flight mill bioassays. 2 Beetles that flew long distances (> 11 km) had a greater body weight and larger wings than beetles that flew short distances (< 1 km). These heavier female beetles should also be more capable pioneers because other studies have shown that body weight is positively correlated with lipid content. 3 Wing and body morphology of females are significant predictors of flight distance; heavy beetles with large wings generally flew further than smaller beetles, although this relationship is heteroscedastic. Dispersion of flight distance values increases with wing loading (weight/wing area) as a result of a cohort of 'lazy' individuals that fly short distances (< 1 km) regardless of flight phenotype. 4 The observed morphology explained less than 20% of the variation in flight capacity, indicating a substantial contribution from other intrinsic factors that remain to be investigated. The present study may have implications for dispersal modelling, providing estimates of flight capacity using morphological measurements.

Spatial variability of hosts, parasitoids and their interactions across a homogeneous landscape

“…Information on parasitoid mobility is scarce and controversial (Jeffs & Lewis, 2013), but the general belief is that parasitoids are less mobile than their hosts (Cronin & Reeve, 2005; Jeffs & Lewis, 2013). However, the ability of insects to disperse is usually associated to body size (Shegelski, Evenden, & Sperling, 2019) and, in our study, the body size of most parasitoids is similar to that of their hosts (unpublished data). We can thus assume similar mobility for hosts and parasitoids.…”

Factors influencing dispersal by flight in bark beetles (Coleoptera: Curculionidae: Scolytinae): from genes to landscapes

“…Although much of this variation can be explained by morphological or physiological factors, some may be genetic, but specific genes that dictate flight capacity in bark beetles have yet to be discovered. Flight mill studies of D. ponderosae illustrate that beetles with similar body condition, size, and mass still exhibit variable flight capacity (Shegelski et al 2019). Multiple approaches to measuring flight capacity and dispersal are required to get an accurate view of dispersal by flight in bark beetles.…”

“…Jactel (1993) uses pronotum width as a proxy for body size; Botterweg (1982) and Forsse and Solbreck (1985) use elytra mass and length, respectively; and studies by Evenden et al (2014) and Anderbrant and Schlyter (1989) use beetle mass. It is important to distinguish between these terms as physical body dimensions often do not predict flight capacity of individual bark beetles (Botterweg 1982;Forsse and Solbreck 1985;Jactel 1993;Shegelski et al 2019).…”

“…Wing beat frequency increases with wing loading (body mass/wing area), inertia, and resistance. Bark beetle wing size and shape influence these measures and affect wing-beat frequency (Atkins 1960) and subsequent flight capability (Shegelski et al 2019). Wing area is one of the most important morphological factors that influence flight capacity in D. ponderosae (Shegelski et al 2019).…”

“…Flight muscle size also correlates with flight capacity in bark beetles. Wing shape and size contributes to flight capacity in some bark beetles (Shegelski et al 2019), but research into specific genes coding for wing structure is lacking. Flight muscle size seems to be equally important in the prediction of flight capacity in both Dendroctonus and Ips, suggesting that the energetic capacity of large Dendroctonus beetles is a key driver of flight capacity.…”