The influence of temperature and photoperiod on the reproductive diapause of two Mexican bean beetle, Epilachna varivestis Mulsant, populations and their cross progeny was determined in laboratory tests. The fertility level of the El Salvador population exceeded that of the Maryland population under both diapause and non-diapause conditions. Changes in photoperiod had a greater impact on diapause in the El Salvador population, while the Maryland strain was more responsive to changes in temperature. Progeny of reciprocal crosses were more fertile than progeny of purebred crosses, suggesting hybrid vigor. Results indicated that in the Mexican bean beetle reproductive diapause is genetically inherited, has some degree of dominance, and that population differences due to temperature and photoperiod are probably adaptations to the specific population environments.

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