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An article describing the structural mechanics of mosquito antennal accessory pulsatile organs was published today in Journal of Experimental Biology.

The antennae of insects are involved in the detection of chemical, tactile, thermal, and auditory stimuli.�� In mosquitoes, the detection of near field sound by the antennae’s Johnston’s organs influences courtship and mating, and the reception of odorant and thermal cues by antennal neurons controls oviposition and host-seeking behaviors.�� Because antennae are intricately involved in essential physiological processes, insects must ensure that molecules required for proper antennal functioning are efficiently transported into and out of these sensory appendages.

In insects, hemolymph (insect blood) propulsion into the antenna is accomplished through the contraction of antennal accessory pulsatile organs (APOs).�� In this paper we use correlative imaging methods to characterize the functional mechanics of antennal accessory pulsatile organs in the African malaria mosquito, Anopheles gambiae.�� Specifically we:

1. 1.Describe the precise location of the mosquito antennal APOs (see image).
   

2. 2.Show that the antennal APOs contract in synchrony at approximately 1 Hz.
   

3. 3.Determine that the antennal APOs contract in a manner that is independent of the heart.
   

4. 4.Measure the directional velocity of hemolymph inside the antennae.
   

5. 5.Describe the structure of the antennal APOs and the antennal vessel.
   

6. 6.Show that the anesthetic agent FlyNap (active ingredient: triethylamine) accelerates both heart and antennal APO contractions rates.
   

7. 7.Construct a model of hemolymph propulsion across the antennal space (see image).
   

Article citation:

Boppana, S., and J.F. Hillyer. 2014. Hemolymph circulation in insect sensory appendages: functional mechanics of antennal accessory pulsatile organs (auxiliary hearts) in the mosquito Anopheles gambiae.�� Journal of Experimental Biology. 217(17):3006-3014.

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Graphical abstract:

Left: Image of the mosquito head showing the location of the antennal accessory pulsatile organs (labeled green).�� Right: Model of hemolymph propulsion across the antennal space.

Article abstract:

Mosquito antennae provide sensory input that modulates host seeking, mating and oviposition behaviors. Thus, mosquitoes must ensure the efficient transport of molecules into and out of these appendages. To accomplish this, mosquitoes and other insects have evolved antennal accessory pulsatile organs (APOs) that drive hemolymph into the antennal space. This study characterizes the structural mechanics of hemolymph propulsion throughout the antennae of Anopheles gambiae. Using intravital video imaging, we show that mosquitoes possess paired antennal APOs that are located on each side of the head's dorsal midline. They are situated between the frons and the vertex in an area that is dorsal to the antenna but ventral to the medial-most region of the compound eyes. Antennal APOs contract in synchrony at 1 Hz, which is 45% slower than the heart. By means of histology and intravital imaging, we show that each antennal APO propels hemolymph into the antenna through an antennal vessel that traverses the length of the appendage and has an effective diameter of 1-2 µm. When hemolymph reaches the end of the appendage, it is discharged into the antennal hemocoel and returns to the head. Because a narrow vessel empties into a larger cavity, hemolymph travels up the antenna at 0.2 mm/sec but reduces its velocity by 75% as it returns to the head. Finally, treatment of mosquitoes with the anesthetic agent FlyNap (triethylamine) increases both antennal APO and heart contraction rates. In summary, this study presents a comprehensive functional characterization of circulatory physiology in the mosquito antennae.

(This post was modified on 9/1/2014 to include the full citation of the article)