Browsing by Author "Brady, J."
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Item Calculation of Anopheline Man-Biting Densities from Concurrent Indoor and Outdoor Resting Samples(1974) Brady, J.; Department of Zoology and Applied Entomology, Imperial College of Science and Technology, LondonS.W.7A continuing problem in malaria epidemiology is the accurate measurement of the manbiting-rate (ma of Macdonald's 1957 formula, h= mabs). Both direct catches of female anophelines as they bite and all indirect sampling methods are subject to biases of different kinds (eg Garrett-Jones and Shidrawi, 1969; Garrett-Jones, 1970). Although there are arguably more accurate methods of sampling, the indirect, pyrethrum'spray-catch'of houses is unquestionably the most productive of anophelines per man-hour. Its weakness is that some females of even highly endophilic species such as Anopheles gambiae invariably leave a house on the night that they feed, and the technique thus only gives an accurate measure of ma when the exophilic proportion of the population is very small. The present paper suggests a means for adjusting this estimate of ma to allow for the proportion of the vector population that is resting outside. When the gonotrophic cycle lasts 2 days, the morning female anopheline population comprises fed and gravid individuals in approximately equal numbers (excluding unfed and pre-gravid females). Sampled during the morning, the outside resting population should therefore be found to consist of a minority of fed mosquitoes-those that left the houses soon after feeding during the previous night-and a larger number of gravid mosquitoes that fed the night before and left either then or as half-gravids 24 hours later. Where densities are high, and natural resting sites not too abundant, this situation may commonly be observed in unsprayed areas (eg Muirhead Thomson, 1951; Brady, unpublished observations in Ghana). When it is, the data can be made use of as follows: letItem Circadian Changes in Central Excitability -the Origin of Behavioral Rhythms in Tsetse Flies and other Animals(1975) Brady, J.; Department of Zoology and Applied Entomology, Imperial College, London, S.W.7Diel changes in seven behavioural responses of male tsetse flies, G.morsitans, were measured under controlled conditions in the laboratory. These responses involved different motor and sensory modalities, and were evoked by stimuli that were either exogenously applied at regular intervals or were ever‐present. Six (possibly seven) of the responses were modulated across the photophase (of LD 12: 12) in the V‐pattern typical of biting behaviour in the field: morning and evening responses were greatest, noon least. Two of these rhythms were shown to persist in constant conditions, indicating that the underlying control is truly circadian. Comparison of the form of an optokinetic response rhythm at high and low stimulus intensities, implied central control of the response modulation. This, plus the close similarity in phase of the different rhythms, is interpreted as indicating circadian changes in central excitatory state (arousal) as the underlying neurophysiological basis of behavioural rhythmicity. It is suggested that the sarrie arousal system controls the comparable, longer and shorter term changes in excitability that result from starvation, sex, etc.Item Laboratory observations on the visual responses of tsetse flies(1971) Brady, J. ; Department of Zoology & Applied Entomology, Imperial College Field station , Ascot BerksThe responsiveness of Glossina morsitans to a slowly moving visual stimulus was investigated under controlled environmental conditions. The stimulus consisted of a 4·5 em. wide vertical black stripe moving past a window at c. 12 em./sec. 12 times a minute. The flies were 30-90 em. distant from this window, and were exposed in groups of 10 (male or female) to the stimulus for 5 minutes, once every hour throughout the 12 hour light of a 24 hour light : dark cycle, from their last feed until incipient death. Responsiveness was measured as: (a) the percentage of flies taking-off, and (b) the total number of take-offs made, during the first 60 seconds of the stimulus (these 2 parameters are strongly positively correlated). Control observations were made hourly for 5 minutes in the absence of the stimulus.Item Second Symposium on Tsetse Fly Breeding in the Laboratory and its Practical Applications(1972) Brady, J.; Department of Zoology and Applied Entomology. Imperial College, London, S.W.7Tsetse flies (Glossina morsitans morsitans) were exposed periodically 10 a slowly moving vertical back stripe in a controlled environment chamber (Brady, 1971). Response to this visual stimulus was by take-off and flight, preferentially orientated towards the stripe. Responsiveness varied markedly with stimulus speed, a log range of which was tested, revealing:Item Spontaneous, Circadian Components of Tsetse Fly Activity(1972) Brady, J.; Department of Zoology and Applied Entomology, Imperial College, London S.W.7 UKThe spontaneous flight activity of Glossina morsitans was monitored in rocking-box actographs in constant conditions under different light régimes. The mean daily time spent in activity in the actographs (12·5 min) accords well with what is estimated for behaviour in the field. In all types of fly tested, a clear ‘V’-shaped diurnal pattern of activity occurred in LD 12 : 12. The morning peak comprised more activity than the evening peak, but for hungry flies roughly the same proportion of the population was involved at each time. The similarity between this spontaneous activity pattern in the laboratory and the diurnal pattern typically observed in the field suggests that it is unnecessary to invoke environmental control to explain the gross form of the latter. In DD a clear circadian rhythm emerged in the activity of teneral flies, though in LL this rhythm damped out after 2 to 3 cycles. These findings are discussed in relation to current theories of circadian rhythms. A linear daily increase in activity occurred during 5 days of starvation in all flies, except pregnant females, whose daily increase followed an exponential pattern, implying that a complex behavioural change results from the act of fertilization.Item The Viability, Fertility and Behaviour of Tsetse Flies (Glossina morsitans) Sterilized by Irradiation Under Various Conditions(1974) Langley, P.A.; Curtis, C.F.; Brady, J.; Tsetse Research, University of Briton, Department of Zoology Applied Entomology and Imperial College of Applied TechnologyGlossina morsitans pupae of known age were irradiated at different times during pupal life. The ages after which irradiation in air did not prevent development and normal eclosion, were identified. Irradiation at the earliest age which allowed normal eclosion of males resulted in decreased adult survival compared with pupae irradiated on the day of eclosion, but in both cases survival was improved by irradiating in an atmosphere of nitrogen. Pupae which had reached the day of peak male eclosion were stored at 10°—11° for 5 days and then produced a predictable flush of adult emergence following irradiation in nitrogen or in air. This technique, or the alternative of irradiation some days before eclosion is expected, would enable several days' collection of pupae to be treated as a single batch for the purposes of release in a sterile male control project. Laboratory measurements of several behavioural parameters showed that adult males, irradiated as pupae, can deviate from normal when compared with unirradiated controls. However, irradiation in nitrogen caused less alteration to behaviour than the lower doses in air required to achieve the same reduction in fertility. Measurements and estimates of the somatic and genetic effects of various irradiation treatments given under described conditions, were used to predict the treatment which would provide the optimal population suppression in a field control project involving the release of sterilized males. Computations have shown that the optimal sterilizing treatment may differ for different target levels of population reduction, and this concept may be of considerable significance in the control of oviparous insects with greater reproductiItem The visual responsiveness of the tsetse fly Glossina morsitans Westw. (Glossinidae) to moving objects: the effects of hunger, sex, host odour and stimulus characteristicscs.(1972) Brady, J. ; Department of Zoology & Applied Entomology, Imperial College of Science & Technology, LondonThe responses of adult Glossina morsitans Westw. to large slowly moving visual stimuli were tested in the laboratory. The standard stimulus, lasting 60 s, consisted of a vertical black stripe (5° wide) on a white background moved 12 times past a window (25° wide) at 13·5°/s. The kinetic responses (take-off), but not orientation towards the stripe, went through a daily cycle with morning and evening maxima some 500% greater than the mid-day response. Kinetic responsiveness in both sexes and all ages of fly increased in an overall linear manner during five days' starvation, though pregnant females were about half as responsive as mature males. The intensity of orientation also increased with starvation, at least in males. For take-off, the minimum stripe width eliciting responses subtended ca 0·6° to the flies, and the optimum angular velocity was 3–7°/s, for orientation, 2–20°/s; the distance of the stripe appeared unimportant. Human odour elicited take-offs in the absence of the visual stimulus, and enhanced the visual responses if these were tested within three minutes of the start of odour stimulation; these effects were much greater in teneral than in mature males. It is concluded that the differences between the sexes and physiological stages of fly are mainly quantitative, and that the accepted view of four physiologically distinguishable phases of behaviour is therefore unsatisfactory. Instead, it is proposed that tsetse behaviour is the outcome of continuously variable responsiveness to visual host stimuli, and not a succession of behavioural entities.Item The Visual Responsiveness of the Tsetse Fly, Glossina Morsitans to Moving Objects: The Effects of Hunger, Sex, Host Odour and Stimulus Characteristics.(1972) Brady, J.; Department of Zoology & Applied Entomology, Imperial College of Science & Technology, London SW7The responses of adult Glossina morsitans Westw. to large slowly moving visual stimuli were tested in the laboratory. The standard stimulus, lasting 60 s, consisted of a vertical black stripe (5° wide) on a white background moved 12 times past a window (25° wide) at 13·5°/s. The kinetic responses (take-off), but not orientation towards the stripe, went through a daily cycle with morning and evening maxima some 500% greater than the mid-day response. Kinetic responsiveness in both sexes and all ages of fly increased in an overall linear manner during five days' starvation, though pregnant females were about half as responsive as mature males. The intensity of orientation also increased with starvation, at least in males. For take-off, the minimum stripe width eliciting responses subtended ca 0·6° to the flies, and the optimum angular velocity was 3–7°/s, for orientation, 2–20°/s; the distance of the stripe appeared unimportant. Human odour elicited take-offs in the absence of the visual stimulus, and enhanced the visual responses if these were tested within three minutes of the start of odour stimulation; these effects were much greater in teneral than in mature males. It is concluded that the differences between the sexes and physiological stages of fly are mainly quantitative, and that the accepted view of four physiologically distinguishable phases of behaviour is therefore unsatisfactory. Instead, it is proposed that tsetse behaviour is the outcome of continuously variable responsiveness to visual host stimuli, and not a succession of behavioural entities.
