Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2015
Publication Date: 8/1/2015
Citation: Prasifka, J.R., Rinehart, J.P., Yocum, G.D. 2015. Nonconstant thermal regimes enhance overwintering success and accelerate diapause development for Smicronyx fulvus (Coleoptera: Curculionidae). Journal of Economic Entomology. 108(4):1804-1809. doi:10.1093/jee/tov173.
Interpretive Summary: The number of red sunflower seed weevils in sunflowers have been inconsistent or declining, particularly in North Dakota. Because of the inconsistency of weevil populations, development of weevil-resistant germplasm and other research have been limited. Weevils spend winters dormant (in diapause) and previously have been stored at low, constant temperatures for research. A constant cold (43 °F) was compared to alternative, non-constant temperatures for storage up to one year. Both alternate temperature treatments (a fluctuating thermal regime, FTR and thermoperiod, TP) produced more adult weevils than constant cold for storage of three months or less, while all temperature treatments were good for medium length (six month) cold storage, and FTR was best for year-long storage. Excluding the very short 14 d cold storage period, a doubling of cold storage time (e.g., three months to six months) decreased the number of days until half of the weevils had emerged by about 10 days. After one year of larval storage, red seed weevil adults successfully infested sunflowers in a plant growth chamber, with damage similar to that observed in field trials. Compared to previous efforts to store weevil larvae, the new method of collection and storage is more effective or more time-efficient, and should permit faster progress in research attempting to improve management of this pest.
Technical Abstract: Recent populations of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae) have been inconsistent or declining, particularly in North Dakota. Consequently, field and laboratory research on weevil biology, including development of resistant germplasm, have been limited. To determine whether cold storage of diapausing larvae could be improved, alternative temperature treatments (fluctuating thermal regime, FTR, and thermoperiod, TP) were tested versus a constant 6 °C for storage up to 365 d. Both alternate (FTR and TP) temperature treatments produced more adult weevils than constant 6 °C for short (42 d, 91 d) storage, while all temperature treatments were good at moderate term (181 d) cold storage, and FTR was best for long (365 d) periods. Excluding the 14 d storage period, which produced too few weevils for comparison, each doubling of cold storage time (e.g., from 42 to 91 d, 91 to 181 d, 181 to 365 d) usually decreased the number of days to 50% relative emergence by ˜ 10 d. After 365 d of larval storage, emerged S. fulvus adults successfully infested sunflowers in a plant growth chamber, with damage per female similar to that observed in field trials. Compared to previous efforts to store weevil larvae, the method of collection and FTR storage is either more effective (greater adult emergence, reduced parasitism) or more time-efficient, and should permit year-round research using S. fulvus adults. Because successful emergence under FTR was > 75% after 365 d of storage, additional research would be required to determine the limits of cold storage for S. fulvus.