MATING ACTIVITY AND STATUS OF OVERWINTERING MONARCH BUTTERFLIES (LEPIDOPTERA, DANAIDAE) IN CENTRAL CALIFORNIA

Based on spermatophore counts, >40% of the overwintering females were mated when they arrived at the Pismo North Beach winter site, San Luis Obispo County California, in October. This percentage remained statistically unchanged until a few weeks before emigration in February. During this period, significantly more mating pairs on the ground were observed within the grove than in an adjacent open field. There was a positive linear relationship between female forewing lengths and the number of spermatophores. Mean female body weights decreased to their lowest level in December but increased in March to a level similar to their arrival weights. This increase, however, is attributed to size (based on forewing length) of the butterflies remaining at the winter site rather than to their multiple-mated condition.