Diapause Regulation in Newly Invaded Environments: Termination Timing Allows Matching Novel Climatic Constraints in the Box Tree Moth, Cydalima perspectalis (Lepidoptera: Crambidae)

Abstract

The association between indirect environmental cues that modulate insect diapause and the actual stressors is by no means granted when a species encounters new environments. The box tree moth, Cydalima perspectalis, is an Asian pest whose rapid invasion in Europe causes considerable economic and ecological impacts. Larvae enter a winter diapause induced by the photoperiod in both native and invaded ranges, but factors that trigger the return to an active phase are still unknown. Yet, identifying them is crucial to understand how diapause end synchronizes with the end of the winter stress encountered in Europe. To test whether activity resumption is regulated by thermal and/or photoperiodic thresholds, or additive effects between these factors often involved in diapause termination, diapausing caterpillars from an invaded area were exposed to crossed treatments at the laboratory. The evolution of diapause rate was monitored over time and compared to that of nearby field sites invaded. A strong positive effect of increasing temperature was found on the rate and dynamics of diapause termination, whereas no compelling effect of photoperiod appeared. Resuming development directly when main stressors fade, not in response to indirect photoperiodic cues that could be mismatched outside native areas, likely contributes to the good match observed between diapause and the new climates that this pest encountered in the invaded range.

Predictive simulation of spring development of Cydalima perspectalis Walker in the South of Russia

“…Considering that the thermal conditions causing the end of diapause in C. perspectalis in winter occur before the temperature rises to the level necessary for the resumption of active feeding of larvae and ontogenesis [4], it was assumed that the need for exposure to low temperatures necessary for the end of diapause at the beginning of the calendar year is fulfilled. After the accumulation of sufficient heat, overwintering ends, and the larvae can resumption their development.…”

“…The increasing intensity of the process of biological invasions associated with climate change and the intensification of international trade of ornamental plants in recent decades has become one of the most acute problems in many countries of the world [1][2][3]. Therefore, issues related to the expansion of adventitious insect species, the mechanisms of their invasion, the main environmental factors and processes that favor or limit the productivity of invasive species are of utmost importance [1,3,4].…”

“…Photoperiodic induction of diapause duration of at least 1.5 months occurs in autumn, when the photoperiod decreases below a key threshold of 13.5 hours [1,4]. However, the conditions under which the end of diapause is observed remain unclear, which makes it difficult to predict the timing of the resumption of insect development in spring [3].…”

“…Despite a large amount of experimental material and generalizations on the manifestation of phenotypic plasticity of temperature norms of C. perspectalis development in various geographical regions [1,3,4,7,9,13], information regarding the forecast of the box tree moth development stages for the rapid provides of pest control action plans is insufficient.…”

Spatial structure of natural boxwood and the invasive box tree moth can promote coexistence

“…In Europe, five to seven larval instars are necessary to the larvae to become pupae for about ten days before emerging as moths [Kawazu et al, 2010]. During the winter, the larvae are at the beginning of their development in stages two, three or even four [Poitou et al, 2020] and form cocoons to enter in hybernaculi [Nacambo et al, 2014]. The moths live up to two weeks during which they reproduce and lay eggs on boxwood leaves.…”