Influence of blood meal on the responsiveness of olfactory receptor neurons in antennal sensilla trichodea of the yellow fever mosquito, Aedes aegypti

In female Aedes aegypti L. mosquitoes, a blood meal induces physiological and behavioral changes. Previous studies have shown that olfactory receptor neurons (ORNs) housed in grooved peg sensilla on the antennae of Ae. aegypti down-regulate their sensitivity to lactic acid, a key component driving host-seeking behavior, which correlates with observed changes in the host-seeking behavior of this species. In the present study, we performed electrophysiological recordings from the most abundant antennal sensillum type, sensilla trichodea. Our results indicate that the response spectra of ORNs contained within most trichoid sensilla do not change in response to blood feeding. However, we observe an increase in sensitivity to primarily indole and phenolic compounds in neurons housed within four of the five functional types of short blunt tipped II trichoid sensilla, both at 24 and 72 h post-blood feeding, which was more pronounced at 24 h than 72 h. Furthermore, sensitivity to undecanone, acetic acid and propionic acid was observed to increase 72 h post-blood meal. Considering the timing of these changes, we believe that these neurons may be involved in driving the orientation behavior of female mosquitoes to oviposition sites, which are known to release these compounds

Neuromodulation in the chemosensory system of mosquitoes - neuroanatomy and physiology

The impact of mosquito vectored disease on global public health is overwhelming. Mosquitoes depend on chemosensory capability for blood-feeding and as such have a highly developed chemosensory system, which consists of peripheral and central components. The repertoire of mosquito behaviors during their life cycle are modified by external and internal factors. The main goal of this thesis is to describe some factors that modulate odor-associated behavior, focusing on biogenic amines, neuropeptides, and physiological state change. I generated a detailed distribution map of serotonin, one of the major biogenic amines in the central and peripheral chemosensory system of Aedes aegypti. The arborization pattern of serotonin-immunoreactive (SI) neurons in the central chemosensory neuropil included the antennal lobe (AL), subesophageal ganglion, tritocerebrum and higher brain centers. In addition, I found SI fibers in the peripheral chemosensory organs: the antennae, the maxillary palps and the labia. Furthermore, to investigate the affects of the gonotrophic and circadian state of mosquitoes on serotonin, dopamine and octopamine levels in the heads of female Ae. aegypti, I used high-performance liquid chromatography coupled with electrochemical detection. Changes in the titer level of these biogenic amines are correlated to flight activity and physiological status of this mosquito. The neuropeptides in the mosquito AL are a highly diverse class of neurochemicals described by matrix assisted laser desorption ionization time-of-flight mass spectrometry of a single AL. I isolated and identified a total of 26 neuropeptides belonging to 10 gene families. Additionally, the cellular distribution of four major families of neuropeptides revealed distinct localization patterns of each of these families in the AL and to other olfactory-associated neuropil areas in the brain. Finally, I employed single sensillum recording to investigate the modulation of odorant receptor neurons housed in the antennal sensilla trichodea after a blood meal. Three functional classes of short blunt-tipped type II sensilla displayed a higher sensitivity after blood feeding to the host and oviposition-associated cues, indole and three phenolic compounds. This study indicates modulation of olfactory behavior occurs at the peripheral level post blood-meal, which may be associated with the physiological status of the mosquitoes

Evolution of Multiple Sensory Systems Drives Novel Egg-Laying Behavior in the Fruit Pest Drosophila suzukii

International audienceThe rise of a pest species represents a unique opportunity to address how species evolve new behaviors and adapt to novel ecological niches [1]. We address this question by studying the egg-laying behavior of Drosophila suzukii, an invasive agricultural pest species that has spread from Southeast Asia to Europe and North America in the last decade [2]. While most closely related Drosophila species lay their eggs on decaying plant substrates, D. suzukii oviposits on ripening fruit, thereby causing substantial economic losses to the fruit industry [3-8]. D. suzukii has evolved an enlarged, serrated ovipositor that presumably plays a key role by enabling females to pierce the skin of ripe fruit [9]. Here, we explore how D. suzukii selects oviposition sites, and how this behavior differs from that of closely related species. We have combined behavioral experiments in multiple species with neurogenetics and mutant analysis in D. suzukii to show that this species has evolved a specific preference for oviposition on ripe fruit. Our results also establish that changes in mechanosensation, olfaction, and presumably gustation have contributed to this ecological shift. Our observations support a model in which the emergence of D. suzukii as an agricultural pest is the consequence of the progressive modification of several sensory systems, which collectively underlie a radical change in oviposition behavior