A team led by Prof. WANG Sibao at Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences (CAS) and the collaborators revealed that Anopheles swarming and mating are coordinately governed by clock genes, light and temperature. This study was published online in Science on January 22.

Swarming is a natural mating behavior of mosquitoes, occurring at dusk. Each swarm contains tens to thousands of males. Females fly into the swarm to select a male for copulation. After insemination, the female would not be receptive to mating for the rest of life. This feature provides a unique advantage for mosquito genetic control. Understanding mosquito mating biology is crucial for the implementation of any genetic control programs via the release of either conventional sterile or genetically engineered males. However, the molecular mechanisms that modulate the swarming and mating activity in mosquitoes remain unclear.

In this study, the researchers used microarray transcriptional analysis to identify genes involved in swarming and mating behaviors by comparing gene expression profiles between swarming and nonswarming male heads of Anopheles mosquitoes. They found that the circadian master genes period (per) and timeless (tim) are markedly upregulated and rhythmically expressed in swarming male heads compared with non-swarming males. Knockdown of per and tim expression affects mating activity of male mosquitoes in both laboratory and semi-field conditions.

Because of the rotation of the earth and day/night cycle, light intensity and environmental temperature exert dramatic changes on organisms. Since Anopheles mosquitoes form swarms at dusk, the researches anticipated that the two most important environmental cues, light and temperature signals, may affect mosquito swarming and mating. Indeed, they found that adverse temperatures and prolonged light exposure during dark periods suppress mating activity, and light and temperature affect mosquito mating via modulating the expression of tim or per genes. These results showed that light and temperature together entrain the circadian clock, influencing the programming of mosquito swarming and mating.

Sex pheromones play important roles in the courtship behavior preceding mating. Many insects use cuticular hydrocarbons (CHC) as sex pheromones for species and sex recognition and courtship, but little is known about the role of CHCs in Anopheles mating, and no sex pheromone has been identified so far in Anopheles mosquitoes.

The researchers found that the desaturase gene desat1 is also upregulated in swarming males, and regulates the production of cuticular hydrocarbons, including heptacosane, in Anopheles mosquitoes. Importantly, mating bioassays further revealed that perfuming virgin Anopheles males with heptacosane markedly enhances mosquito mating activity. They further found that desat1 is a clock-controlled gene in mosquitoes and that light inhibits its transcription and reduces the production of CHCs. These results indicated that the synthesis of male cuticular heptacosane is dynamically regulated.

The increasing global threat of emerging and reemerging mosquito-borne diseases poses a threat to human health. Currently, the control of malaria vectors focuses on the use of chemical insecticides. Due to the rapid emergence and spread of insecticide resistance, alternative tools are urgently needed to control mosquito populations. This study provides mechanistic insights on the molecular, environmental and chemical factors regulating Anopheles swarming and mating behaviors, and contributes to the understanding of mating mechanisms, which may lead to vector control strategies targeting insect reproductive behavior.

Mosquitoes transmit various human infectious diseases. Anopheles mosquitoes are the vector of malaria. For mosquito control. although the sterile insect technique (SIT) has achieved successes in the control of other dipteran pests, earlier mosquito SIT programmes often have conflicting results because of a lack of understanding of male mating biology, especially in terms of the ability of mass-reared male mosquitoes to communicate, courtship and mate with wild female mosquitoes.