HINDSIGHT BY GENITALIA - PHOTO-GUIDED COPULATION IN BUTTERFLIES

1. Butterflies have two pairs of extraocular photoreceptive neurons on the genitalia. Here we report that the genital photoreceptors have a crucial role in achieving copulation. 2. We first investigated mating behavior of the butterfly Papilio xuthus in an outdoor cage. The matin g behavior consists of six steps: the male approaches the female (1), maneuvers into a ventor-to-ventor position with the female (2), search es the female's genitalia (3), clasps the genitalia (4), the pair copu lates (5), and finally separates (6). 3. We bilaterally ablated the P1 pair of photoreceptors, in the males, and observed mating behavior wi th virgin females. Of the intact males 66% copulated successfully, whe reas only about 25% of the treated males could copulate. About 40% of P1 ablated males stopped the mating behavior during step 3: the males could not locate the female's genitalia. P1 ablation in females did no t have a clear effect in this study. 4. Electrophysiological measureme nts showed that the P1 response of a male drops sharply when it correc tly locates the female's genitalia. We hypothesize that the sharp drop in the P1 response informs the male that the female's vagina is corre ctly positioned for penis insertion. The P1 ablated males never experi ence such a response drop, as there is no P1 response to begin with.