Analysis of a complex vertical copulatory-courtship display in the yellow fever vector Sabethes chloropterus

Sabethes chloropterus (Von Humboldt) (Diptera: Culicidae), an arboreal mosquito vector of the yellow fever virus, perches on vertical surfaces, where airborne males patrol for potential mates and mating occurs. Laboratory analysis of 26 virgin mating pairs partly confirms and greatly extends an earlier description suggesting that males perform a courtship ritual. A male approaches a female by hovering behind her, moving toward her from one side, reaching toward her and occasionally touching her with his closest midleg, and eventually seizing her wing with that midleg and inverting beneath her, forelegs against the substrate. Immediately after male alignment with the female, the pair enters a superficial genital-coupling phase, in which the male's extended gonostyli are linked to the female, and he proceeds sequentially through four stages of midleg oscillations (MLOs): Alternate I, Synchronous I, Double-flex, and Synchronous II. Following one or more genital thrusts, the pair shifts to a full-copulation phase, which lasts only up to 6 s, during which the genitalia are clasped and insemination occurs. The male raises his midlegs and hindlegs in succession, then performs Alternate II MLO until the female kicks him and he is released. Nineteen (73%) of the 26 pairs successfully completed the entire sequence, including genital shift and full copulation, taking an average of 3.7 min. Features of the display that might determine success were not evident. Reversions in the chain of events occurred, but linear progression of stages and phases was characteristic of nearly all matings. The male's approach, however, lacked stereotypic form and probably is not part of the courtship.