Hearing of malaria mosquitoes is modulated by a beta-adrenergic-like octopamine receptor and serves as insecticide target
Malaria mosquitoes acoustically detect their mating partners within large swarms that form transiently at dusk. Indeed, male malaria mosquitoes preferably respond to female flight tones during swarm time. This phenomenon implies a sophisticated context- and time-dependent modulation of mosquito audition, the mechanisms of which are largely unknown. Using transcriptomics, we identify a complex network of candidate neuromodulators regulating mosquito hearing in the species Anopheles gambiae. Among them, octopamine stands out as auditory modulator during swarm time. In-depth analysis of octopamine auditory function shows that it affects the mosquito ear on multiple levels: it modulates the tuning and stiffness of the flagellar sound receiver and controls the erection of antennal fibrillae. We show that two a- and ß-adrenergic-like octopamine receptors drive octopamine's auditory roles and demonstrate that the octopaminergic auditory control system can be targeted by insecticides. Our findings highlight octopamine as key for mosquito hearing and mating partner detection, and as a potential novel target for mosquito control. Overall design: To investigate expression, and circadian pattern of expression of transcripts in Anopheles gambiae mosquito ears we conducted the following: First, we entrained mosquitoes, in environmental incubators, to 12H:12H light/dark cycle with 1-hour ramped light transition to simulated dawn and dusk (ZT0-ZT1 and ZT12-ZT13, respectively; ZTX is the formalised notation of an entrained circadian cycle's phase). Temperature and relative humidity were set constantinside the incubators throughout the circadian day, at 28 °C and 80% respectively. Mosquitoes were exposed to the circadian entrainment in the incubators for three days before performing any experiment. Then, on day four of circadian entrainment, 35 male and 35 female mosquitoes were removed from the incubators at six different circadian time points (ZT0, ZT4, ZT8, ZT12, ZT16, ZT20), and we collected their Johnston's organs (JO; the mosquito's "internal ear"). This procedure was repeated 3 times, resulting in three biological replicates of JO samples at each circadian time point. Finally, we performed RNA sequencing of the samples, and conducted transcript expression, differential expression (between males and females), and circadian expression analyses on the sequenced data.