Date of Award:

5-1-1971

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Entomology

Committee Chair(s)

Ting H. Hsiao

Committee

Ting H. Hsiao

Committee

James A. Gessaman

Committee

Wilford J. Hanson

Abstract

The developmental stage which is responsible for the photoperiodic induction of diapause in the alfalfa weevil was determined by subjecting an increasing number of developmental stages to a long-day photoperiod (16 hours) and subsequently transferring them to a short-day photoperiod (8 hours). Adults which did not oviposit by 90 days after emergence were considered to be in diapause. Exposure of the larval and pupal stages to the long-day photoperiod resulted in 32-47% diapausing adult females, which was similar to a control group reared entirely at the short-day photoperiod. However, when the adult stage was exposed to the long-day photoperiod for 1-4 weeks, the incidence of diapause increased to 70-100%. This indicates that the early adult stage is responsible for the photoperiodic induction of diapause in the alfalfa weevil. It was found that as more of the developmental stages were exposed to the long-day photoperiod, the mean emergence to oviposition times increased correspondingly, indicating that the photoperiod has a cumulative effect on the sexual maturation of the female alfalfa weevil. When the alfalfa weevils were reared in growth chambers having daily temperature fluctuations of 55-85, 50-90, and 45-95 F and a photophase of 8 hours, the 45-95 group had the highest mortality(59. 0%), but the shortest development time(24. 0 days). The 55-85, and 50-90 F groups had a mortality of 49.0 and 52. 0% and a development time of 25. 91 and 24. 88 days respectively. These developmental times were significantly shorter than those of a control group reared at a constant tmperature of 70 F. The lowest incidence of diapause was found in the 55-85 F group, which had a 9. 3% diapause as compared to 35. 4% in the 70 F control group, whereas the highest incidence of diapause was found in the 45-95 F(70. 2%). The 50-90 F group had 25. 5% diapause which was not significantly different from the control group. The shortest mean emergence to oviposition time was found in the 55-85 F group(48.0 days) as compared to 65 days in the control group. These findings indicate that the photoperiodic response of the alfalfa weevil is very much modified by the temperature to which it is exposed. The results also indicate that a fluctuating temperature of 55-85 F and a photophase of 8 hours is the most suitable for continuous laboratory rearing of the alfalfa weevil.

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