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Abstract
Larvae of the bean blister beetle, Epicauta gorhami (Coleoptera: Meloidae), feed on
grasshopper eggs in soil and undergo hypermetamorphosis. This beetle undergoes larval
diapause in the fifth instar as a pseudopupa, a form characteristic of hypermetamorphosis
in meloid beetles. This pseudopupal diapause is maintained for a long period if the
larvae are kept under continuous diapause-inducing short-day conditions. In the present
study, the effects of temperature and photoperiod on termination of pseudopupal diapause
in E. gorhami were examined using pseudopupae obtained under 12L-12D at 25°C. Diapause
was terminated by exposure to low or high temperature, but not by transfer to long-day
conditions. The pseudopupal stage comprises diapause and post-diapause phases despite
its unchanging appearance. The optimum low temperature for diapause termination was
10-15°C, and a higher or lower temperature was less effective. There was an individual
variation in the low temperature requirement for diapause termination and post-diapause
development may not occur until this requirement is satisfied. Although under natural
conditions pseudopupae may encounter low temperatures that are effective for diapause
termination at different ages, our results show that pseudopupae at various ages respond
similarly to low temperature exposure. This response may ensure that resumption of
development synchronizes in a population.