Investigating landing and take-off contact dynamics of host-seeking Anopheles coluzzii malaria mosquitoes using frustrated total internal reflection

Abstract

To avoid detection during a bloodmeal, a mosquito must minimize contact forces during attachment and detachment contact while maintaining sufficient grip to insert their proboscis and feed. Measuring contact mechanics of the mosquito is technically challenging due to the small length and force scales. Because of this, many aspects of blood feeding are still poorly understood. We developed an optic measurement set-up that enables the observation of contact dynamics when mosquitoes are host-seeking and blood feeding. Using frustrated total internal reflection (FTIR) we were able to record contact dynamics of freely flying mosquitoes at a spatial resolution of 25µm2 per pixel and a temporal resolution of 500 Hz. While useful given its non-invasiveness, FTIR as a technique may lack reproducibility due to the subjectivity in defining an intensity threshold that signifies contact. At these time and length scales, low signal-to-noise ratio may amplify variations in contact areas measured given selections in intensity thresholds. We developed a systematic approach to select contact thresholds for large image sets, allowing for standardized high-throughput FTIR studies. Our results suggest that probing behaviour, characterized as rapid pulling of the fore and mid legs towards the body during contact, might be less related to surface evaluation via sensing than previously thought, and more related to establishing sufficient grip to insert the proboscis. This new perspective illustrates the need for further investigation into the contact dynamics of mosquitoes during blood feeding to understand the mechanisms that enable the transmission of vector-borne diseases, such as malaria, between hosts.