Behavioral studies of inhibition and integration in the mosquito Culiseta inornata (Williston)

Abstract

A study was made of the interaction in the central nervous system of sensory input arising from the simultaneous application of opposing stimuli to receptors on the tarsi and labella of the mosquito. Stimulating chemosensory hairs on the tarsi with 5 M NaCl failed to inhibit the labellar response to sucrose at concentrations above 0.125 M. At lower sucrose concentrations there was a decrease in the number of mosquitoes responding. The application of 5 M NaCl to the tarsal receptors elevated the labellar threshold for sucrose in all subjects tested. This influence of the salt was expressed whether acting on the tarsi in an ipsilateral or contralateral manner. Stimulating the tarsal hairs with 2 M sucrose resulted in a labellar response to NaCl at concentrations of 0.50 M and lower. Ordinarily NaCl is rejected at all concentrations by this mosquito. Evidence was obtained which indicated that the labellar response to NaCl was mediated by the water receptor rather than by the salt receptor.The presence of contact chemoreceptor organs on the tarsi and labella of the mosquito provides a convenient means of investigating central nervous system inhibition and integration. Under appropriate circumstances, stimulation of chemosensory hairs on the tarsi with sucrose elicits the proboscis response and, likewise, the same stimulus applied to the labellar hairs evokes the labellar response (Frings and Hamrum, '50; Feir et al., '61). In contrast with these results, the application of NaCl to groups of chemosensory hairs on either of these organs will not elicit a feeding response (Owen, unpublished). At high concentrations NaCl acts as a strong rejection stimulus and, conversely, sucrose is highly stimulating as an acceptable material. The interaction in the central nervous system of sensory input arising from simultaneous application of these two opposing stimuli to sensory hairs on the tarsi and labella was the basis of this study.Much that is known about inhibition in insects has been learned from studies of the taste receptors of the blowfly, P h m i a regina. Dethier ('53) reported that NaCl, HCI and propanol could act either ipsilaterally or contralaterally in preventing the proboscis response to sucrose. He also demonstrated that the prevention of proboscis extension to both water and sucrose by unacceptable compounds was predom-J. EXP. ZOOL., 166: 301306.inantly a central nervous system phenomenon. It was also noted by Dethier ('55) that when unacceptable compounds were mixed with sucrose and applied to the tarsi of the blowfly the rejection thresholds increased as the sugar concentration was increased. Arab ('59) found that brief stimulation of a few chemosensory tarsal hairs of the blowfly with 2 M NaCl resulted in an immediate rise in the threshold of the labellar hairs for sucrose. Furthermore, he noted that the central excitatory state of a hungry fly could be raised by brief stimulation of its tarsi with 1 M sucrose. Dethier et al. ('66) demonstrated that for a hungry fly which is water satiated, stimul...

Fine Structure of the Sense Organs on the Labella and Labium of the Mosquito Aedes aegypti (L.)

“…Results from behavioral studies have indicated that mosquito labellar hairs are sensitive to water, sugar solutions and unacceptable compounds [1][2][3][4][15][16][17][18]. Electrophysiological studies have also shown that these hairs are stimulated by water, sugar, and NaCl [5,15,19].…”

The mosquito taste system and disease control

“…By contrast, bitter compounds and high concentrations of salts elicit aversive responses. Ammonium chloride or high concentrations of salts evoke rejection responses, such as proboscis withdrawal, and inhibit feeding behavior (23,(43)(44)(45)(46). These responses may have evolved in part to prevent ingestion of harmful food sources.…”

Assessment of diet choice by the yellow fever mosquito Aedes aegypti

“…The feeding cues in these simple diets are selected based on the composition of the known mosquito food sources, nectar and honeydew: the three most abundant and one of the less abundant sugars; all 20 naturally‐occurring amino acids; the salt, sodium chloride; and two plant secondary metabolites, caffeine and quinine, previously demonstrated to be detected and discriminated by a variety of insects (Siddiqi & Rodrigues, 1980; Meunier et al , 2003; Hiroi et al , 2004; Thorne et al , 2005; Moon et al , 2006). The two‐choice assay employed in the present study may be more representative of a natural environment than the previously relied upon no‐choice and labellar response assays (Owen, 2005) because it provides the mosquito with the opportunity to feed in an environment that presents a hierarchy of choice: to assess the quality of the two meals on offer and to make a choice. The aim is to produce a basic characterization of mosquito diet acceptance behaviour using a panel of ecologically relevant feeding cues and thus provide the basis for future work assessing mosquito taste‐related behaviours in the context of their natural and more complex diets.…”