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Biomedical subjects

P A Langley

Publications and source records attributed to P A Langley.

At least 19 recordsLinked to original sources
PubMed1999

Ultrastructural localization of unique neurosecretory granules in the corpora cardiaca of the stable fly, Stomoxys calcitrans, and the tsetse fly, Glossina morsitans.

Ultrastructural analysis of the corpora cardiaca of the stable fly, Stomoxys calcitrans, and the tsetse fly, Glossina morsitans, revealed the presence of elementary neurosecretory granules (ENG) unique to the intrinsic neurosecretory cells (INC) of these species. In addition to electron-dense spheres, the INC of the corpus species. In addition to electron-dense spheres, the INC of the corpus cardiacum of the stable fly contain electrondense angular granules, either square or rectangular in shape, while the INC of the tsetse fly contain electron-dense spindle-shaped ENG. The distinctive granules of these INC can be traced within nerves to their sites of storage and release, eliminating the need for labeling with artificial probes. Although the INC of the corpus cardiacum of most species have been found to be fuchsinophilic, neither the INC of the stable fly nor the tsetse fly are aldehyde-fuchsinophilic. These peptigenic cells offer neuroendocrinologists a unique opportunity to study the physiology and biochemistry of neurosecretory cells.

Animals↗
PubMed1994

Understanding tsetse flies.

The discovery that tsetse flies are the vectors of African trypanosomosis, causing sleeping sickness in man and nagana in cattle, occurred at the start of a rapidly expanding colonialism in sub-Saharan Africa. Hence, the first research on the fly was largely taxonomic, coupled with a painstaking ecological approach to determine the identities and distribution limits of the different species. This was followed by closer attention to the physiology of the fly, both from the academic standpoint as related to its survival and reproduction in the field, and from the standpoint of its vectorial capacity. There are still conflicting hypotheses concerning the maturation of trypanosomes within the fly. Increasing concern for the environment led to a ban in the developed nations on the use of DDT as an insecticide which had been used successfully for tsetse control in Africa. This was followed by a ban on the use of organochlorine insecticides in general, and no doubt the next restrictions will be on the use of organophosphates and upon synthetic pyrethroids which have already been banned in the UK for the control of houseflies. Fortunately, research on the role of olfactory and visual stimuli of the tsetse, in the location of potential hosts, led to an improvement in methods for monitoring fly populations by means of traps and targets upon which the flies alight. So successful are such devices that, when treated with an insecticide, they can be used to sustain an increase in natural mortality in fly populations to such an extent that these populations decline to manageable levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The Tsetse Research Laboratory.

The Tsetse Research Laboratory in Bristol was opened in December 1962, with the initial objective of developing techniques for rearing tsetse flies on a large scale outside Africa. Its work has, however, extended greatly since then. This article highlights the research undertaken at the Laboratory, not only on the breeding of tsetse flies but also on various aspects of their biology and control.

Animals↗
PubMed1990

Formulation of pyriproxyfen, a juvenile hormone mimic, for tsetse control.

A topical dose, in 1 microliter acetone, of 0.02 microgram-2-[1-methyl-2-(4-phenoxyphenoxy) ethoxy] pyridine, the juvenile hormone mimic pyriproxyfen (S-31183, Sumitomo Chemical Co.), caused an adult female tsetse, Glossina morsitans morsitans Westwood, to produce non-viable offspring for the whole of her life. Using 14C labelled pyriproxyfen it was determined that as little as 0.001 microgram transferred to the in utero larva was sufficient to arrest development in the pupal stage. A formulation in vegetable oil was prepared for treating black cotton cloth targets which caused females to pick up 0.1 microgram active ingredient (a.i.) by tarsal contact during 1 min of exposure. Males exposed similarly for between 1 and 5 min transferred up to 0.016 microgram a.i. to females if they mated immediately after treatment. Doses as low as 0.01 micrograms in 10 microliters oil cm-2 on black cotton cloth targets caused females to produce non-viable offspring for at least two reproductive cycles following exposure. However, a dose of 0.1 microgram in 10 microliters oil cm-2 was necessary for an exposed male to cause disruption of the reproductive potential of his mate. This juvenile hormone mimic has potential to induce sterility via both sexes of tsetse using treated targets or traps under field conditions.

Animals↗
PubMed1988

Juvenile hormone mimics as effective sterilants for the tsetse fly Glossina morsitans morsitans.

The development of puparia of Glossina morsitans morsitans Westwood was disrupted by topical applications of the juvenile hormone mimics S-methoprene (the resolved enantiomer of 11-methoxy-3,7,11-trimethyl-2,4-dodecadienoic acid 1-methyl ester) (Zoecon), S21149 (propionaldoxime-0-4-phenoxyphenoxyethylether) (Sumitomo), or S31183 (2-[1-methyl-2-(4-phenoxyphenoxy)ethoxy]pyridine) (Sumitomo) dissolved in acetone. Puparia so treated during the first 4 days of life suffered developmental abnormalities, the severity of which were dose-dependent. Similarly, puparia produced by adult females treated with these compounds were abnormal. Dose-response data showed that effects were greatest with S31183 and least with S-methoprene. Abnormalities in the form of abdominal lesions and wing crumpling were typical of flies emerging from puparia produced by S-methoprene-treated females. However, arrested development at the red eye and pigmented seta stage within the puparium were typical of offspring of females treated with S21149 and S31183. A dose of 2 micrograms per female of S31183 was sufficient to prevent emergence of offspring produced for the rest of the life of the fly. The same dose resulted in partial recovery of females treated with S21149 some 18 days following treatment. Treatment with 2 micrograms S-methoprene did not suppress completely the production of normal offspring and recovery was complete some 27-35 days after treatment. Exposure of males to 20 micrograms S31183 did not impair their ability to inseminate females; transfer of material during copulation was sufficient to prevent the production of viable offspring by their mates.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Development of a system for sterilizing tsetse flies, Glossina spp., in the field.

Various autosterilizing systems were evaluated on natural populations of Glossina pallidipes Austen and G.morsitans morsitans Westwood in Zimbabwe. These involved a clear plastic tower of two or three chambers mounted at the cage position on a trap. Inside one chamber flies could be exposed to the vapour phase of the chemosterilant bisazir, P,P-bis (1-aziridinyl)-N-methylphosphinothioic amide. The system was designed to encourage flies to enter the sterilizing chamber, delaying their exit for sufficient time to expose them to a sterilizing dose. This was accomplished in the most effective system by restriction of the exit to one small hole (6 mm diameter) at the roof-side junction. The number of flies remaining in the chamber declined exponentially. The rate of exit was directly proportional to the density of flies in the sterilizing chamber and to the number of exit holes. The probability of a fly being in this chamber for at least 1 or 7 min (the times taken for female and male G.m.morsitans respectively to receive an ED50) was 0.84 and 0.67 respectively with one fly present. With sixteen flies, these probabilities were 0.76 and 0.18 respectively. Results suggest that it may be possible to develop a cheap, safe and efficient autosterilizer for use on tsetse traps.

Animals↗
PubMed1982

Sex recognition pheromone in the tsetse fly Glossina pallidipes Austen.

Sexual responses of adult male G. pallidipes towards baited decoys show that a contact sex pheromone for this species is present in the hydrocarbon fraction of the adult female cuticle. Results are consistent with the view that the pheromone is a C35 compound and is present in sufficient quantity in newly emerged females to elicit maximum responses from males. Thus, maturation of sexual responsiveness is considered to be behavioral in females of this species.

Animals↗
PubMed1978

Sex pheromone of the tsetse fly: isolation, identification, and synthesis of contact aphrodisiacs.

Sex pheromones isolated from the cuticle of the female tsetse fly, Glossina morsitans morsitans Westwood, release mating behavior in the male fly at ultrashort range or upon contact with baited decoys. Three active components were identified as 15,19-dimethylheptatriacontane, 17,21-dimethylheptatriacontane, and 15,19,23-trimethylheptatriacontane. Chemical and biological comparisons show that the natural and synthetic compounds are identical.

Animals↗
PubMed1975

Pathogen transmission in relation to feeding and digestion by haematophagous Arthropods.

The blood feeding habit, especially among opportunist feeders such as tabanids and Stomoxys is known to result in transmission of diseases for which the vectors are not the obligate or alternate hosts. Thus, mechanical transmission of trypanosomes such as T. vivax can occur in cattle herds outside tsetse fly areas where tabanids are actively feeding. In the case of Yaws, mechanical transmission of the spirochaetes by eye flies (Hippelates pallipes) in the West Indies is thought to be most likely. The spirochaetes remain motile in the pharynx and oesophageal diverticula for several hours but are apparently immobilised in the midgut (Kumm & Turner, 1936). There is apparently no development ofspirochaetes in the fly. They have been shown to pass through houseflies, but in mechanical transmission, biochemical transformation or adaptation of the pathogen is not implied. Virus transmission is common among arthropods and transovarial transmission to succeeding generations is frequent in mites and ticks. Although Yellow Fever virus is not transovarially transmitted by its vector Aedes aegypti, the mosquito only becomes infective some time after ingesting an infected blood meal (Chandler, 1955). Thus, metabolic or biochemical changes or adaptations in the virus or in the vector are in some way implicated, as they must also be in transovarially transmitted viruses. However, the causal relationships between virus infectivity and vector physiology are poorly understood. As with virus infections, those disease organisms possessing a cyclical host/vector relationship will possess a variable infectivity potential which is not necessarily related to the abundance of any of the organisms in the cycle. Clearly, feeding behavior and host preferences of the vector are important in determining the rate and extent of disease transmission, and such parameters can be quantified in epidemiological studies. However, a complete understanding of the factors concerned in cyclical disease transmission also depends on a knowledge of the physiology of the organisms involved, and particularly of the interdependence of their physiologies. The subject is vast, and it is proposed to illustrate the problems involved and the progress made, by reference largely to trypanosome transmission by tsetse flies (Glossina spp.).

Adaptation, Physiological↗