DIFFERENTIAL RELEASE OF DIAPAUSE IN THE EARWIG FORFICULA-AURICULARIA AS INDICATOR OF RESPECTIVE CONTRIBUTION OF 2 COHORTS TO THE REPRODUCTIVE GENERATION

Persistence of a two-cohort reproductive strategy in the earwig Forfic ula auricularia would seem to imply a selective advantage to females w hich complete two reproductive maternal cycles. This advantage is not, however, obvious because (1) females which rear a second cohort succe ssfully abandon their first cohort larvae more rapidly and this may lo wer their chances of survival and because (2) only some females, less than 25 % of the total, succeed in their second parental phase. Each a nnual generation, sum of the two cohorts, becomes adult in the summer and vitellogenesis occurs before the end of autumn. The first egg layi ngs and parental phases are usually stimulated by exposure of over win tering and diapausing females to cold. Because of the fluctuating cond itions in the field (specially the slow spring warm up) females from t he two cohorts lay at the same period at the end of winter and cannot be distinguished in this respect. We describe how to estimate the comp osition of a reproductive population in terms of females from the two preceding larval cohorts: about 50 % of reproductive females in the ge neration observed came from the second, yet smaller at hatching, cohor t. The few females which reared a second cohort successfully may then indeed be at an appreciable selective advantage. Traits associated wit h achievement of a second maternal phase would then also be subjected to strong positive selection.