Submitted to: Physiological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2009
Publication Date: 9/1/2009
Citation: Rinehart, J.P., Yocum, G.D., Chirumamilla-Chapara, A., Boetel, M.A. 2009. Supercooling Point Plasticity During Cold Storage in the Freeze-Tolerant Sugarbeet Root Maggot Tetanops myopaeformis. Physiological Entomology. 34(3):224-230.
Interpretive Summary: The sugarbeet root maggot is a major insect pest in many of the sugarbeet producing areas of the United States. This insect damages sugarbeet plants by feeding on the roots as larvae. In the field, it overwinters as a fully grown larvae buried in the soil. In the laboratory, the larvae exhibit a remarkable ability to be stored for up to five years in cold temperatures. In either case, the larvae of the sugarbeet root maggot are freeze tolerant, exhibiting the ability to survive the formation of ice crystals in their bodies. This study investigates the survival and supercooling point (temperature at which the insect freezes) for this species. We discovered that the freezing temperature of the larvae changes significantly during cold storage, highlighted by a large range of freezing points in older larvae. However, when a group of larvae are frozen, thawed, and frozen again, their freezing point of the second freeze changes to a temperature similar to what is seen in much younger larvae. How does this all affect overwintering in the field? To answer this question, we recorded the temperature at various soil depths on an hourly basis through an entire winter. Our data shows that the overwintering larvae are protected from extreme temperatures when buried in the soil, and in many cases, the temperature below ground does not reach the temperature at which their body freezes at. Hence, their behavior is to avoid freezing. Further study on how these observations occur, and how they affect winter survival will be important to understanding this economically important species.
Technical Abstract: The sugarbeet root maggot, Tetanops myopaeformis (Röder), overwinters as a freeze-tolerant 3rd instar larva. While most larvae are thought to overwinter for only one year, some may exhibit prolonged diapause in the field. In the laboratory, they can live for over five years using a combination of diapause and post-diapause quiescence. In this study, we investigated the cold survival strategies of these larvae during storage by measuring their supercooling points in combination with survival data. We found that SCPs change significantly during storage, highlighted by a marked increase in the range of SCPs recorded, although the ability to tolerate freezing is not affected. Additionally, we have found that a freezing event “re-focuses” the SCPs of aged larvae to levels similar to those seen at diapause initiation. This change in SCPs is dependant not only on the initial freezing event, but on the parameters of the incubation period between freezing events as well. Finally, we monitored the temperatures of larval overwintering microhabitats during the 2007-2008 boreal winter. Our results indicate that while overwintering larva are physiologically freeze-tolerant, they may in essence be freeze avoidant during overwintering via microhabitat selection.