Mating Behavior and sperm competition in fruit flies, with reference to difference between Hawaiian and Japanese melon flies.

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Comparison of mating behavior of Hawaiian and Okinawan melon flies (Bactrocera cucurbitae) was made based on field and laboratory observations. In Okinawa, melon fly males form lek on non-host plants in evening and each male waits female sitting on a leaf. When a female comes the male couts and sometimes, after female mate choice, is accepted by her. In Hawaii, on the other hand, males don't form leks, but actively fly to find females. They court to sitting females. Our field studies showed that this difference is due to difference in population density in the two areas. Even in Okinawa, males seek for females when the density was low, where the wating tactics of males was not effective to find females. Thus males adaptively change their mating tactics in different social conditions.Courtship sounds of Hawaiian melon fly males were almost the same as those of Okinawan males, but there was subtle difference. Behavior and morphological characters in relation to sex pheromone emission of Hawaiian melon fly males were the same as those of Okinawan males. These facts suggest that there is no species-level difference between Hawaiian and Okinawan melon flies.Experimental studies with Okinawan melon flies showed that (1) sperm longevity in female spermathecae was short and this was important for variation of P2 values in relation to mating interval, and (2) remating of females was suppressed by long copulation, possibly due to transportation of male accessary gland substance to female body. Existence or absence of sperm in spermathecae did not affect the remating suppression.