Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2008
Publication Date: 4/1/2008
Citation: Chirumamilla, A., Yocum, G.D., Boetel, M.A., Dregseth, R.J. 2008. Multi-year survival of sugarbeet root maggot (Tetanops myopaeformis) larvae in cold storage. Journal of Insect Physiology. 54(4):691-699. Interpretive Summary: The sugarbeet root maggot, Tetanops myopaeformis (Röder) (Diptera: Ulidiidae), is a major economic insect pest of sugarbeet in the Red River Valley of Minnesota and North Dakota, and it is also a problem for growers in the Western United States. Typically univoltine and freeze tolerant, the root maggot survives the winter by undergoing diapause as a matured third-instar larva. The sugarbeet root maggot has been successfully maintained alive in cold storage for up to six years. Although these field-collected larvae presumably entered storage in diapause, it was not known whether they were maintaining the same physiological status during long-term storage. Prolonged diapause resulting from either a simple extension of normal winter diapause, or re-entering a second diapause following the winter diapause could be allowing this phenomenon to occur. Alternatively, the larvae could be in a state of post-diapause quiescence and waiting for the appearance of favorable temperatures. To develop a better understanding of various physiological phenomena associated with diapause and long-term storage and to investigate the probable differences and similarities between them, we conducted four independent experiments involving respirometry, biochemical analyses of external and internal lipid content, evaluation of differential gene expression patterns, and assessments of post-storage survival, emergence, and reproductive performance on T. myopaeformis larvae. Results from these experiments revealed that extended survival of T. myopaeformis larvae in long-term cold storage is facilitated by two mechanisms, with majority of them in post-diapausal quiescence and a smaller fraction in a state of prolonged diapause.
Technical Abstract: Sugarbeet root maggots (Tetanops myopaeformis), as third-instar larvae have been successfully maintained in cold (6 ± 1ºC) storage for up to six years. To test the hypothesis that this long term survival in storage is facilitated by larvae undergoing prolonged diapause, comparative studies on respiration, lipids, and gene expression patterns were conducted comparing field-collected diapausing larvae with one-, two-, and five-year laboratory stored larvae. Additional assessments were made on post-storage survival, emergence, and reproductive fitness of stored larvae. Respirometry at 5 and 20ºC revealed no difference between respiration rates of initially diapausing and long-term stored larvae. A 15-degree increase in temperature elevated respiration in both diapausing and stored larvae, with CO2 levels ranging between 8- and 14-fold higher at 20ºC than at 5ºC. Similarly, 6- to 10-fold increases in O2 levels were observed at the higher temperature. Increasing temperatures caused a major shift in respiratory quotient (RQ) values from 0.5 to approximately 1.0 in five-year stored larvae and December field-collected diapausal larvae. Usage of lipid reserves was significant over five years of storage. Lipid usage was low from diapause to one year of cold storage, but significant from one to two years and non-significant from two to five years of cold storage. A transcript with sequence similarity to fat body protein 2 (Fbp2) gene, was expressed in diapausing larvae, and was not detectable in one-, two-, and five-year stored larvae. Survival and emergence studies of stored larvae revealed mixed populations of diapausing (6-16% of larvae that did not pupate) and post-diapausing (63-83% of larvae pupated) insects, with a high rate of pupation (63%) and emergence (54%), even after four years in cold storage. Therefore, extended survival of T. myopaeformis larvae in long-term cold storage is facilitated by two mechanisms, with majority of them in post-diapausal quiescence and a smaller fraction in a state of prolonged diapause.