The light at the end of the tunnel: photosensitivity in larvae of the mountain pine beetle (Coleoptera: Curculionidae: Scolytinae)

Abstract

Investigations of light sensitivity and its physiological effects on insects developing within subcortical tree tissues are limited, presumably due to the assumption that cryptic microhabitats are completely devoid of light. In this study, we documented light-mediated behaviour and opsin gene expression in larvae of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), an extremely important forest insect that is well adapted for development beneath the bark of pine (Pinus Linnaeus; Pinaceae) trees and is eyeless in the larval stage. Larvae were negatively phototactic, as they selected dark over light microhabitats in phototaxis assays. We recovered long-wavelength opsin transcripts from all life stages, including eggs and larvae, suggesting that D. ponderosae is photosensitive throughout its entire life cycle. Our results imply that photosensitivity contributes to immature D. ponderosae survival and that extraocular photoreception could be common among bark beetle larvae.

Autumn shifts in cold tolerance metabolites in overwintering adult mountain pine beetles

“…Mountain pine beetle phenology is known to be most responsive to temperature changes, with hormonal regulation and photo period playing little part in cold acclimation [13]. Photoperiod, historically thought to have little effect on cold hardening, may be involved to some degree as new evidence suggests that mountain pine beetle larvae respond negatively to light, even when located in a sub-cortical environment [19]. Reliance on temperature occasionally results in phenological delays causing an extension of the life cycle beyond one year.…”

Autumn shifts in cold tolerance metabolites in overwintering adult mountain pine beetles

“…Mountain pine beetle phenology is known to be most responsive to temperature changes, with hormonal regulation and photo period playing little part in cold acclimation (Régnière and Bentz 2007). Photoperiod, historically thought to have little effect on cold hardening, may be involved to some degree as new evidence suggests that mountain pine beetle larvae respond negatively to light, even when located in a sub-cortical environment (Wertman et al 2018). Reliance on temperature occasionally results in phenological delays causing an extension of the life cycle beyond one year.…”

Shedding new light upon circadian emergence rhythmicity in the mountain pine beetle (Coleoptera: Curculionidae: Scolytinae)

“…For example, insect behaviours under circadian control may include eclosion, oviposition, egg hatching, and movement (summarised in Felisberti et al 1997 andLampel et al 2005). Direct and circumstantial evidence from a diverse set of entomological studies indicates that a diversity of cryptic (physically concealed, see definition by Wertman et al 2018) insects are capable of photoperiodic time measurement (Shintani et al 1996;Doležal and Sehnal 2007;Shintani 2011;Friedrich 2013). Photoperiod is known to influence development rate, including diapause programming, in certain subcortical tree-tissue developing beetles (Coleoptera) (Shintani et al 1996;Doležal and Sehnal 2007;Shintani 2011), and is implicated in the entrainment of circadian behavioural rhythms in cave beetles (Friedrich 2013).…”

“…Dendroctonus ponderosae larvae, like all scolytid beetle larvae, lack external ocular organs (stemmata) (Jordal 2014), and photoperiodic information for circadian clock entrainment must therefore be received extraocularly (Wertman et al 2018). The photoperiodic stimuli that reach D. ponderosae larvae developing beneath the bark most likely consist of long-wavelength light (480-600 nm), which is considered important to the ecology of low-light-adapted insects (Jackowska et al 2007;Friedrich et al 2011;Wertman et al 2018).…”

“…Dendroctonus ponderosae larvae, like all scolytid beetle larvae, lack external ocular organs (stemmata) (Jordal 2014), and photoperiodic information for circadian clock entrainment must therefore be received extraocularly (Wertman et al 2018). The photoperiodic stimuli that reach D. ponderosae larvae developing beneath the bark most likely consist of long-wavelength light (480-600 nm), which is considered important to the ecology of low-light-adapted insects (Jackowska et al 2007;Friedrich et al 2011;Wertman et al 2018). It is therefore probable that long-wavelength-sensitive opsin proteins are the photoreceptors responsible for stimulating physiological responses in cryptic insects (Wertman et al 2018), including those observed in subcortical tree-tissue developing beetles (Shintani et al 1996;Doležal and Sehnal 2007;Shintani 2011).…”