In fact, when individual mating attempts are observed, the proportion that lead to successful copula formation is consistently relatively low (16% 40, 28% 43, and 37% 42). There are, however, multiple published accounts of females displaying a variety of active behaviours to evade, deter, or displace prospective partners including evasive flight manoeuvres, leg pushes, kicks, or thrusts, and abdominal jerks or tilts 18, 21, 40, 41, 42, 43, 44, 45.
Indeed, the absence of readily observable selective behaviours within mating swarms has raised the question of whether females exert any choice whatsoever in this system 6, 22, 26. In particular, the role of female choice and the degree to which it influences mating outcome is not known. Insemination rate is typically used to assess male performance 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, yet the specific behavioural differences that underlie variation in success are poorly defined. Mosquito swarms have thus been said to resemble lek mating systems 15, 26, with males clustering around and competing within locations attractive to receptive females 27, who approach and are mated, while receiving no paternal care contribution 15.įundamentally, successful mating inside a swarm requires males to detect and intercept females in flight (coupling), engage their genitalia (copula formation), and transfer semen (insemination) 12. aegypti predominantly mate only once in a lifetime 24, 25, it is thought that the likelihood that any particular male will successfully copulate is low compared to the total number participating within the group. Copulation-which can take between 9 and 31 seconds to complete 12-has been observed both inside and outside the swarm, and with the pair in flight or at rest 10, 22, 23. At this point a quick reorientation takes place such that the pair are “venter-to-venter” 12, 21, a position that facilitates genital engagement. Males detect a nearby female via the sounds produced by her beating wings 18, 19, 20, and pursue and seize her in mid-air. Individual females approach-likely in search of a blood-meal source 10, 13-and enter swarms in much lower numbers 11, leading to a sex ratio that is skewed towards males 8, 9. Although the precise mechanisms that mediate swarm formation in this species are not fully understood 9, 14, both chemical and acoustic cues have been proposed 15, 16, 17. In the yellow fever mosquito, Aedes aegypti, small groups of males aggregate in close proximity to vertebrate hosts 10, 11, 12, 13. Numerous species of mosquito are known to mate in aerial swarms 6, 7, 8, 9. Releasing males with high mating success will facilitate programme success and ultimately improve the feasibility and sustainability of these control strategies in the long-term. Ensuring that released males are able to effectively compete for and mate with wild females is a key component of these initiatives 5. Mass release of sterile and transgenic males to manage wild mosquito populations is currently being integrated into vector control programmes 1, 2, 3, 4.
Our findings provide a clearer understanding of the relationship between acoustic interactions and mating performance in mosquitoes, offering insights which may be used to target improvements in laboratory reared lines. Harmonic convergence (wingbeat frequency matching) was detected more often in successful attempts, coinciding with the transition to stabilised paired flight and subsequent genital contact. Rapid frequency modulation of flight tones was observed in all interactions up to acceptance of the male.
We identified two distinct phases of acoustic interaction. Successful males were kicked at a reduced rate and sustained paired contact-flight for longer than those that were rejected. In most couplings, males were actively displaced by female kicks in the early phases of the interaction, while flight cessation prior to adoption of the pre-copulatory mating pose also inhibited copulation. Using synchronised high-speed video and audio recordings, we quantified behavioural and acoustic features of mating attempts between tethered female and free-flying male Aedes aegypti. Despite the importance of mosquito mating biology to reproductive control strategies, a mechanistic understanding of individual mating interactions is currently lacking.