Multi-year survival of sugarbeet root maggot (Tetanops myopaeformis) larvae in cold storage

To test the hypothesis that long-term survival of sugarbeet root maggot in storage is facilitated by larvae undergoing prolonged diapause, respiration and gene expression patterns of field-collected diapausing larvae were compared with those of 1-, 2-, and 5-year laboratory-stored larvae. Additional assessments were made on post-storage survival, emergence, and reproductive fitness of stored larvae. Respirometry, carried out at 5 and 20 degrees C revealed no differences among respiration rates of initially diapausing and long-term stored larvae. A 15 degrees increase in temperature elevated respiration in both diapausing and stored larvae, with levels of CO2 release ranging between 8- and 14-fold higher at 20 degrees C than at 5 degrees C. Similarly, 6-10-fold increases in O2 consumption levels were observed at the higher temperature. A transcript with sequence similarity to the fat body protein 2 (Fbp2) gene was highly expressed in diapausing larvae, and trace levels were expressed in some samples of 1-year stored larvae. However, no expression was detected in 2- and 5-year stored larvae. Survival and emergence studies of stored larvae revealed mixed populations of diapausing (i.e., the 5-17% of larvae that did not pupate) and post-diapausing (62-84% of larvae pupated) insects, with a high incidence of pupation (62%) and emergence (47%), even after 4 years in cold storage. Therefore, extended survival of Tetanops myopaeformis larvae in long-term cold storage is facilitated by two mechanisms, with a majority of larvae in post-diapause quiescence and a smaller fraction in a state of prolonged diapause.