Temperature-dependent development of the great European spruce bark beetle Dendroctonus micans (Kug.) (Coleoptera: Curculionidae: Scolytinae) and its predator Rhizophagus grandis Gyll. (Coleoptera: Monotomidae: Rhizophaginae)

Abstract

Dendroctonus micans is an invasive species that has spread throughout Britain, which prompts the question: how is the voltinism of this pest and its biocontrol agent Rhizophagus grandis affected by climate? Dendroctonus micans and R. grandis were reared at a range of constant temperatures. Lower developmental threshold temperature (LDT) and day degree (DD) requirements for the egg, larval and pupal stage of D. micans were estimated to be 7.4 °C 153 DD, 6.6 °C 527 DD and 7.2 °C 126 DD, respectively. At 12.5, 15 and 17.5 °C, prior to prepupal cell formation, fifth-instar larvae underwent a diapause, which has not been observed previously in this species. Prepupal development rate also did not increase linearly with temperature. For R. grandis, the LDT and DD requirements for the egg, larval, prepupal and pupal stages were 5.7 °C 84 DD, 6.2 °C 263 DD, 8.1 °C 90 DD and 6.8 °C 178 DD, respectively. At 12.5 and 15 °C, most prepupae failed to pupate, which is indicative of a facultative diapause. The key developmental parameters reported in the present study may be used to model the phenology of the beetles throughout their range, providing better-timed control strategies or to predict outbreak risk under climate change as a result of reduced biocontrol effectiveness.