Peculiar liquid-feeding and pathogen transmission behavior of Aedes togoi and comparison with Anopheles sinensis

Enhanced heat tolerance of viral-infected aphids leads to niche expansion and reduced interspecific competition

Vector-borne pathogens are known to alter the phenotypes of their primary hosts and vectors, with implications for disease transmission as well as ecology. Here we show that a plant virus, barley yellow dwarf virus, increases the surface temperature of infected host plants (by an average of 2 °C), while also significantly enhancing the thermal tolerance of its aphid vector Rhopalosiphum padi (by 8 °C). This enhanced thermal tolerance, which was associated with differential upregulation of three heat-shock protein genes, allowed aphids to occupy higher and warmer regions of infected host plants when displaced from cooler regions by competition with a larger aphid species, R. maidis. Infection thereby led to an expansion of the fundamental niche of the vector. These findings show that virus effects on the thermal biology of hosts and vectors can influence their interactions with one another and with other, non-vector organisms.

Effects of oil-film layer and surfactant on the siphonal respiration and survivorship in the fourth instar larvae of Aedes togoi mosquito in laboratory conditions

Mosquitoes transmit various diseases; thus, controlling them is necessary to prevent mosquito-borne infections. Unlike flying adult mosquitoes, those in the immature stages are easy to control because of being restricted to their habitats found in an aquatic environment. In this study, we aimed to evaluate of respiration and survivorship in the larvae of Aedes togoi. The mechanism of actions of the oil-film layer and the surfactant as well as their effects on the siphonal respiration of submerged Aedes togoi larvae were analyzed by checking the survival time of mosquito larvae against oil-film layer and surfactant, and conducting experiments using a siphon-model. Compared with an impermeable membrane used for reference (762.4 min; average time in all cases), the survival time of mosquito larvae was 5% longer for the oil-film layer (808.1 min) and 40% longer for the surfactant (1086.9 min). The surface of the siphon was changed from hydrophobic to hydrophilic by addition of a surfactant. In addition, the surface tension and wettability have a significant influence on the opening and closing of siphon. This study would be helpful for understanding the basic mechanism of physical control measures for disturbing the siphonal respiration of mosquito larvae in a way of dissolved oxygen and surface tension. The present results would guide the establishment of effective control measures for mosquitoes.

Burst mode pumping: A new mechanism of drinking in mosquitoes

Mosquitoes transport liquid foods into the body using two muscular pumps in the head. In normal drinking, these pumps reciprocate in a stereotyped pattern of oscillation, with a high frequency but small stroke volume. Do mosquitoes modulate their neuromotor programs for pumping to produce different drinking modes? More broadly, what are the mechanical consequences of a two-pump system in insects? To address these questions, we used synchrotron x-ray imaging and fluid mechanical modeling to investigate drinking performance in mosquitoes. X-ray imaging of the pumps during drinking revealed two modes of pumping: continuous reciprocation with multiple small strokes, and a newly discovered ‘burst mode’ involving a single, large-volume stroke. Results from modeling demonstrate that burst mode pumping creates a very large pressure drop and high volume flow rate, but requires a massive increase in power, suggesting that continuous pumping is more economical for drinking. Modeling also demonstrates that, from one mode of pumping to the other, the mechanical role of the individual pumps changes. These results suggest that the advantage of a two-pump system in insects lies in its flexibility, enabling the animal to pump efficiently or powerfully as demanded by environmental considerations.

Superb feeding behavior of Aedes albopictus transmitting Zika virus

Disease-mediated mosquitoes have been receiving much attention, as the World Health Organization recently declared the Zika virus a global public health emergency. Mosquitoes transmit pathogens that cause various tropical diseases including malaria, dengue fever and yellow fever as well as Zika virus. The vector efficiency of mosquitoes depends on their blood-feeding characteristics and the mechanics of their blood-sucking pump system, but only a few studies have attempted to investigate these key issues. In this study, we demonstrate the rapid and gluttonous liquid-feeding characteristics of Ae. albopictus which transmits Zika virus can be explained by similar proportion of two blood-sucking pumps and accelerated liquid intake driven by fast expanding of pumps. Our results provide insight into the vector efficiency of Ae. albopictus in terms of feeding velocity, pumping frequency, liquid-intake rate, and wall shear stress.

Comparison of the tracheal systems of Anopheles sinensis and Aedes togoi larvae using synchrotron X-ray microscopic computed tomography (respiratory system of mosquito larvae using SR-μCT)

Mosquito-borne diseases, such as malaria, dengue fever, and Zika virus, are serious global health issues. Vector control may be an important strategy in reducing the mortality caused by these diseases. The respiratory system of mosquito larvae in the water has to inhale atmospheric oxygen as aquatic organisms. In this study, the three-dimensional (3D) structures of the dorsal longitudinal trunks (DLTs) of the tracheal systems of Anopheles sinensis and Aedes togoi were compared using synchrotron X-ray microscopic computed tomography. DLT respiratory frequencies were also investigated. Interestingly, the larvae of the two mosquito species exhibit tracheal systems that are both morphologically and functionally distinct. A. sinensis hangs horizontally under the water surface, and has a smaller DLT volume than A. togoi. In contrast, A. togoi hangs upside down using a siphon by fixing its tip to the water surface. The frequency of peristaltic movement in A. togoi is higher than that of A. sinensis. These differences in the structures and breathing behaviors of the respiratory systems of mosquito larvae provide new insights into the tracheal systems of mosquito larvae, which should help develop novel effective control strategies targeting mosquito larvae.