Could phenotypic plasticity limit an invasive species? Incomplete reversibility of mid-winter deacclimation in emerald ash borer

Abstract

The emerald ash borer (Agrilus planipennis, Coleoptera: Buprestidae) is a wood-boring invasive pest devastating North American ash (Fraxinus spp.). A. planipennis overwinters primarily as a freezeavoiding prepupa within the outer xylem or inner bark of the host tree. The range of this species is expanding outward from its presumed introduction point in southwestern Michigan. We hypothesized that loss of cold tolerance in response to mid-winter warm spells could limit survival and northern distribution of A. planipennis. We determined whether winter-acclimatised A. planipennis prepupae reduced their cold tolerance in response to mid-winter warm periods, and whether this plasticity was reversible with subsequent cold exposure. Prepupae subjected to mid-winter warm spells of 10 and 15°C had increased supercooling points (SCPs) and thus reduced cold tolerance. This increase in SCP was accompanied by a rapid loss of haemolymph cryoprotectants and the loss of cold tolerance was not reversed when the prepupae were returned to -10°C. Exposure to temperatures fluctuating from 0 to 4°C did not reduce cold hardiness. Only extreme warming events for several days followed by extreme cold snaps may have lethal effects on overwintering A. planipennis populations. Thus, distribution in North America is likely to be limited by the presence of host trees rather than climatic factors, but we conclude that range extensions of invasive species could be halted if local climatic extremes induce unidirectional plastic responses.

Insects in Fluctuating Thermal Environments

“…Storage under FTs also holds applications for mass-rearing of insects for pollination (98,124) and potential applications for sterile insect technique (21). FTs could also be exploited to deacclimate insects (103), and thus to reduce cold tolerance of pests as part of a thermal quarantine procedure. Similarly, the negative impacts of repeated cold or heat stress (80) could be leveraged to control stored product pests (59), but this has not been well-explored.…”

“…Interestingly, the benefits of FTs appear to apply only to freezeavoiding and chill-susceptible species: repeated freeze-thaw is damaging to freeze tolerant species (80). In addition, long warming interruptions can lead to deacclimation and loss of cold tolerance (103,113). For example, overwintering emerald ash borer (Agrilus planipennis) prepupae irreversibly lost their cold tolerance after exposure to +10°C for more than a week, reducing survival of subsequent cold exposures (103).…”

“…In addition, long warming interruptions can lead to deacclimation and loss of cold tolerance (103,113). For example, overwintering emerald ash borer (Agrilus planipennis) prepupae irreversibly lost their cold tolerance after exposure to +10°C for more than a week, reducing survival of subsequent cold exposures (103).…”

An invitation to measure insect cold tolerance: Methods, approaches, and workflow

“…mid-winter thaws). For example, Sobek-Swant et al (2012) found that winter-acclimatized freezeavoidant emerald ash borer prepupae had increased SCPs and decreased glycerol concentrations after exposure to mid-winter warm spells (+10 and +15 °C), and that this deacclimation was not reversed when the prepupae were returned to -10 °C. Deacclimation is rarely included in cold tolerance studies, but is clearly relevant when attempting to understand the plasticity of cold tolerance, particularly in relation to variable environments.…”

Modest Effects of Host on the Cold Hardiness of Emerald Ash Borer †

“…This holding time allowed minor injuries from extraction to become visible, but was not long enough for the overwintering larvae to lose cold acclimation [27].…”