Pupal diapause
of Coloradia pandora: Thermal constraints on
successful pupation
Copyright
E. A.
Gerson 1 , R. G.
Kelsey 1 & D. W. Ross 2
1 U.S.
Forest Serv., PNW Research Station, 3200 Jefferson Way,
Corvallis, OR 97331, USA; 2 Dept. of Forest Science, Oregon
State Univ., Corvallis, OR 97331, USA
The pandora
moth, Coloradia pandora, is a native lepidopteran
that periodically defoliates large areas of pine forest in
the western U.S. In central Oregon, pupation occurs in loose
soil over winter, and the pupal phase generally lasts 12 to
13 months of a 2-year life cycle. To determine the minimum
cold storage time required to break diapause we held pupae
at 5 o C for 8 to 24 weeks, then incubated them at 25 o C
and measured the time until adults emerged. The minimum cold
time required under these conditions was 12 weeks, but
emergence rates were highest (87.5%) for 14 to 18 weeks at 5
o C. Cold storage in excess of 20 weeks resulted in
emergence rates of less than 40%. In a separate experiment,
1000 pupae were maintained in field enclosures for 3 years
while soil temperature was monitored. Seventy-two percent of
these pupae emerged in Year 1. Prolonged (extended) diapause
was observed in only 0.6% of the sample population. Soil
temperatures fell below 5 o C for ? 21.7, 22.9, and 25.1
weeks over the three consecutive winters, and the minimum
soil temperature was -2 o C. Based on results from the cold
storage experiment, the 72% emergence rate for Year 1 in the
field was higher than expected for ? 21.7 weeks of soil
temperatures below 5 o C. However, the soil temperature
profiles indicated that pupae used in the cold storage
experiment probably were exposed to several weeks of cold
soil in the field prior to collection for the lab study. In
this case, emergence rates in the lab and field experiments
correspond well. Soil temperature monitoring in the field
revealed the duration of cold may be lethal to a large
proportion of the pupal population in winters such as Year 3
with 25.1 weeks below 5 o C. From the bell curve for
emergence rates established in the lab experiment, less than
40% of pupae would be expected to successfully complete
diapause after a long winter (such as Year 3), compared to
the 72% successful pupation rate observed for the shorter
winter of Year 1. Together, the laboratory and field studies
suggest duration of cold during the pupal phase is a
variable, but potentially significant, mortality factor for
pandora moths in central Oregon.
Index terms:
pandora moth, Saturniidae, rearing, adult emergence, winter
mortality.
Copyright:
Session 13 – INSECT PHISIOLOGY, NEUROSCIENCES, IMMUNITY
AND CELL BIOLOGY Symposium and Poster Session, ABSTRACT
BOOK II – XXI-International Congress of Entomology,
Brazil, August 20-26, 2000
and
Gerson, E.A., R.G.
Kelsey, and D.W. Ross. 1999. Pupal diapause of Coloradia
pandora Blake (Lepidoptera:Saturniidae). Pan-Pacific
Entomol. 75:170-177.
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