Edward E. Davis

Lactic acid-sensitive receptors on the antennae of the mosquito,Aedes aegypti

Summary1.A pair of chemoreceptor neurons sensitive to lactic acid (LA) was identified in the grooved-peg (A3) sensilla on the antennae of the mosquito,Aedes aegypti.2.One chemoreceptor responded to LA with an increase in spike frequency, whereas the other chemoreceptor exhibited a decrease in spike frequency when presented with LA.3.CO2, either alone or in combination with LA, elicited no change in spike frequency of either LA-sensitive neuron, indicating that the behavioral synergism of CO2 and LA occurs centrally and not at the primary receptor level.4.Water vapor induced such a weak excitatory response in both LA-sensitive neurons that their involvement in the detection of water vapor is questioned.5.The insect repellent, DEET, inhibited both LA-sensitive neurons. DEET plus LA was additive in the LA-inhibited cell, whereas the LA response of the LA-excited cell was attenuated by DEET.6.The reaction spectra of the LA-sensitive neurons were determined using pure compounds (Table 1).7.The importance of LA in the host-finding behavior of the mosquito is discussed.

Temperature responses of antennal receptors of the mosquito,Aedes aegypti

Summary1.A pair of thermoreceptor units was identified in the sensilla coeloconica at the tip of the antennae on the mosquito,Aedes aegypti.2.One thermoreceptor was warm-sensitive and responded with a phasic-tonic increase in spike frequency to sudden increases in temperature. The second thermoreceptor was coldsensitive, responding with a phasic-tonic increase in spike activity to sudden decreases in temperature.3.The mean tonic spike activity of both the cold and warm receptors increased with increasing temperature to a peak of 30 imp/sec at 26‡ C for the cold receptor and 35 imp/sec at 28.5‡ C for the warm receptor. The tonic activity declined as the temperature was increased further. The maximum phasic sensitivity was observed with small temperature changes (δ T = ± 0.2‡C). This was 136 imp/sec/‡C temperature drop in the cold receptor and 130 imp/ sec/‡ C rise in the warm receptor.4.The importance of temperature in the host-seeking and “attack” behavior of the mosquito is discussed.

Regulation of sensitivity in the peripheral chemoreceptor systems for host-seeking behaviour by a haemolymph-borne factor in Aedes aegypti

Abstract The taking of a blood meal and subsequent development of eggs by a female mosquito is reported to suppress host-seeking behaviour. This change in behaviour may be partly mediated by changes in certain chemosensitive antennal afferent neurones that influence the behaviour of female mosquitoes. Electrophysiological activity of the lactic acid-excited neurons to lactic acid—a normal host-attractant substance—is depressed following a blood meal. This reduction in lactic acid sensitivity is coincident with the reported inhibition of host-seeking behaviour. The reduction in lactic acid sensitivity is reversible; this sensitivity returns to the pre-blood-fed level following oviposition. Like the inhibition of host-seeking behaviour, the reduced lactic acid sensitivity is due to a transfusable, haemolymph-borne factor. A role for the peripheral sensory system in the control of behaviour in female mosquitoes is discussed.

Development of lactic acid-receptor sensitivity and host-seeking behaviour in newly emerged female Aedes aegypti mosquitoes

Abstract The temporal patterns for the development of sensitivity in the lactic acid-excited neurones of the antennal grooved-peg sensilla and for the initiation of host-seeking behaviour by newly emerged virgin female Aedes aegypti mosquitoes were determined and compared. A 1:1 correlation between the presence of a high sensitivity to the host attractant, lactic acid, in the lactic acid-excited neurones and the presence of host-seeking behaviour was observed. This finding supports the notion that changes in the activity of the peripheral sensory system are sufficient, although perhaps not the only means, to control host-seeking behaviour of female mosquitoes.

A behavioural and sensory analysis of host-seeking behaviour in the diapausing mosquito Culex pipiens

Abstract Diapausing Culex pipiens females maintained in diapause-inducing conditions fail to exhibit host-seeking behaviour for at least 30 days after adult emergence. This behavioural hiatus is characterized by the absence of high-sensitivity antennal receptor responses to the host attractant lactic acid. Non-diapausing females readily exhibit host seeking and invariably have antennal receptors with high lactic acid sensitivity. This difference in receptor sensitivity may be restricted to the lactic acid-sensitive receptors as other antennal receptors (specifically, those sensitive to putative oviposition-site attractants) are unaffected by the diapause state.

Response of the antennal receptors of the male Aedes aegypti mosquito

Abstract Extracellular recordings of the spike discharge patterns of single chemoreceptor neurons in the antennae of male Aedes aegypti mosquitos were obtained and compared with similar recordings made from homologous sensilla on the antennae of female A. aegypti. In both male and female mosquitos, the grooved-peg sensilla were associated with two types of neurons sensitive to lactic acid—one excited by lactic acid and the other one inhibited by lactic acid. The short, blunt-tipped sensilla trichodea Type II (A2-II) of the male mosquito house chemosensory neurons sensitive to volatile chemical substances associated with sources of plant nectar, whereas in the female this information is provided by the long, sharp-tipped sensilla trichodea and the female A2-II sensilla respond to oviposition-site attractants.

A receptor sensitive to oviposition site attractants on the antennae of the mosquito, Aedes Aegypti.

Abstract The blunt-tipped sensilla trichodea Type II on the antennae of female Aedes aegypti mosquitos has been found to be specific for the perception of chemical substances associated with the location of a suitable oviposition site by gravid female mosquitos. The chemosensory neurons associated with the sensilla respond to substances reported in the literature to be oviposition attractants; this response is characterized by an increase in spike frequency proportional to the intensity of the stimulus. Comparison of neurophysiological data with behavioral results reported in the literature suggests that the two sets of data are correlated.

Ammonia-sensitive neurones on the first tarsi of the tick, Rhipicephalus sanguineus

Abstract Two types of ammonia-sensitive neurones were found on the first tarsi of the tick, Rhipicephalus sanguineus. These cells were located in the anterior pit and medial groups of sensilla on the dorsal surface of the tarsus. Ammonia-sensitive neurons showed phasic and/or tonic response patterns that were proportional to the ammonia intensity over the range of 0.2 to 100 × 10−9 moles/sec. Both types of ammonia-sensitive neurones were ‘slow-adapting’ in that they maintained their tonic responses to ammonia during periods of prolonged stimulation. Individual ammonia-sensitive cells varied in sensitivity to ammonia. As a group, the anterior pit neurones were more sensitive than the medial group neurones throughout the concentration range examined. The high degree of specificity for ammonia of ammonia-sensitive neurones was shown by their lack of responsiveness to most other stimuli presented at physiological intensities. Preliminary behavioural studies reveal that low levels of ammonia elicit questing responses from R. sanguineus. This finding, coupled with the electrophysiological evidence for primary afferent neurones sensitive to low levels of ammonia, supports the concept that ammonia plays a role in directing host-seeking or other behaviours of R. sanguineus.

Role of the fat body in the regulation of host-seeking behaviour in the Mosquito Aedes aegypti

Abstract Following a blood meal that initiates oocyte development, the host-seeking behaviour of Aedes aegypti mosquitoes is inhibited by a haemolymph-borne factor that is released in response to a humoral signal from a vitellogenic ovary. This inhibition is accompanied by a decrease in the sensitivity of the peripheral lactic acid receptors. Implantation of corpora allata, medial neurosecretory cells, or terminal abdominal ganglia from blood-fed donors could not induce the inhibition in sugar-fed recipients. However, fat body transplanted from blood-fed into sugar-fed females suppressed host-seeking behaviour as well as the sensitivity of lactic acid receptors, suggesting that the source of the behavioural inhibitor is the fat body. Resting-stage ovaries from other mosquito species inhibited host-seeking after the A. aegypti host was fed on blood only if the fat body was activated by the donor ovary.

Structure-response relationship of the lactic acid-excited neurones in the antennal grooved-peg sensilla of the mosquito Aedes aegypti

Abstract The lactic acid-excited afferent neurones associated with the antennal grooved-peg sensilla of the mosquito were presented with a series of chemical stimuli selected to determine the relationship between the molecular structure of the chemical stimulus and the responses of the lactic acid-excited neurones. The responses of single lactic acid-excited neurones indicated that the optimal stimulus configuration for these neurones was a 3-carbon, α-hydroxy, monocarboxylic acid, i.e. lactic acid. The range of sensitivities found in the sample of lactic acid-excited neurones is discussed in relation to a potential mechanism for enhancing the overall sensitivity of the system to chemical stimuli. The efficiency of the grooved-peg sensillum as an olfactory receptor does not appear to be affected by the fact that it has only a single terminal pore.