Mosquito's mouthparts are exquisite and complex, in which the hypopharynx is located in the middle of the lower lip, with a tongue-like shape and teeth at the end. It can regulate the opening of salivary gland duct. When mosquitoes suck blood, dengue virus enters the human body along the salivary gland with saliva. The cutting function of mosquito mouthparts is accomplished by the big jaw and the small jaw, both of which have fine teeth at the ends. The maxilla and mandible of male mosquitoes have degenerated and lost the function of piercing the skin. Only taking nectar can maintain a short life, so only female mosquitoes have the ability to spread diseases.

The blood-sucking behavior of female mosquitoes is regulated by two fleshy pumps, one of which is located in the sinus pump from the mouth to the pharynx, which is used to control the base of the food passage; The other is pharyngeal pump, which is used to regulate the movement of digestive tube from mouth to middle chest. These two pumps are separated from the midgut of mosquitoes by sphincter. When mosquitoes suck blood, they will first explore the skin surface with the lip flap and repeatedly puncture the skin to choose the most suitable blood sucking position, and the selection criteria are mainly based on the distribution density of microvessels in the skin. Mosquitoes are supported by their lower lip when sucking blood, and then insert the oral needle into the skin. Oral acupuncture is a structure composed of upper lip, big jaw and small jaw, which can be operated as a whole. The lower lip left outside the skin is arched inward.

When mosquitoes suck blood, the oral needle can directly pierce the capillaries, or use the movement of the mouthparts to cut the capillaries and form a blood pool before sucking blood. During the biting process, the virus enters the human body with saliva. In fact, the mouthparts of mosquitoes are not only a flying syringe, but their salivary glands at least contain

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Plant protein. At present, it is known that mosquito saliva contains neutrophil capture factor, which will aggregate neutrophils at the bite, causing inflammatory reaction, redness and papules. People often feel stimulated after being bitten, which is an allergic reaction of the bitten person to mosquito saliva. These allergic reactions may be related to the increased concentration of eosinophils and histamine in the body.

Another component of saliva, tachykinin, can dilate microvessels and help mosquitoes suck blood smoothly. In addition, the saliva of Aedes aegypti contains adenylate hydrolase, which can hydrolyze adenosine triphosphate (ATP) and adenosine diphosphate (ADP) into adenosine monophosphate (AMP) and inorganic phosphorus. The composition has the effect of inhibiting platelet aggregation. Because not all mosquitoes have this enzyme, this enzyme is not a necessary condition for successful blood sucking.