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Biomedical subjects

G A Vale

Publications and source records attributed to G A Vale.

7 recordsLinked to original sources
PubMed2005

User-friendly models of the costs and efficacy of tsetse control: application to sterilizing and insecticidal techniques.

An interactive programme, incorporating a deterministic model of tsetse (Diptera: Glossinidae) populations, was developed to predict the cost and effect of different control techniques applied singly or together. Its value was exemplified by using it to compare: (i) the sterile insect technique (SIT), involving weekly releases optimized at three sterile males for each wild male, and (ii) insecticide-treated cattle (ITC) at 3.5/km(2). The isolated pre-treatment population of adults was 2500 males and 5000 females/km(2); if the population was reduced by 90%, its growth potential was 8.4 times per year. However, the population expired naturally when it was reduced to 0.1 wild males/km(2), due to difficulties in finding mates, so that control measures then stopped. This took 187 days with ITC and 609 days with SIT. If ITC was used for 87 days to suppress the population by 99%, subsequent control by SIT alone took 406 days; the female population increased by 48% following the withdrawal of ITC and remained above the immediate post-suppression level for 155 days; the vectorial capacity initially increased seven times and remained above the immediate post-suppression level for 300 days. Combining SIT and ITC after suppression was a little faster than ITC alone, provided the population had not been suppressed by more than 99.7%. Even when SIT was applied under favourable conditions, the most optimistic cost estimate was 20-40 times greater than for ITC. Modelling non-isolated unsuppressed populations showed that tsetse invaded approximately 8 km into the ITC area compared to approximately 18 km for SIT. There was no material improvement by using a 3-km barrier of ITC to protect the SIT area. In general, tsetse control by increasing deaths is more appropriate than reducing births, and SIT is particularly inappropriate. User-friendly models can assist the understanding and planning of tsetse control. The model, freely available via http://www.tsetse.org, allows further exploration of control strategies with user-specified assumptions.

Animals↗
PubMed2004

Biological and chemical assays of pyrethroids in cattle dung.

Bioassays were developed in Zimbabwe to measure pyrethroid in cattle dung. These and chemical assays then estimated concentrations in dung from treated oxen and elucidated risks to dung fauna. Laboratory bioassays with adult beetles (Histeridae and Scarabaeinae, including Copris, Digitonthophagus, Onitis and Sisyphus spp.) and muscoid larvae (Musca lusoria Wiedemann) indicated that the LC50 of pyrethroids, as ppm in the wet weight, averaged 0.04 for deltamethrin pour-on, 0.25 for deltamethrin dip, 0.22 for alphacypermthrin pour-on, 0.10 for cyfluthrin pour-on, 0.23 for cypermethrin dip and 0.63 for flumethrin dip. Field bioassays involved artificial dung pats of 800 g, deployed in woodland and inspected after 24 h to record insects dead and alive. Beetles were most abundant in the wet season. Muscoid larvae were less seasonal. The LC50 of insecticides in the field confirmed laboratory indications. Adult Diptera (muscoids and Sgifidae) were not repelled or killed until the deltamethrin concentration reached 10 ppm. Pat dispersal by dung fauna and termites (Microtermes spp.) was halved by deltamethrin at 0.1-1 ppm. Scavenging of dead beetles by ants was greatest with small beetles (< 15 mm long) uncontaminated with insecticide. Dips and pour-ons of deltamethrin on cattle gave residues of about 0.01-0.1 ppm in dung produced in the fortnight after application. About 1.6% of the deltamethrin applied was transferred to dung. Deltamethrin and alphacypermethrin in dung showed no detectable degradation in 64 days. Contamination levels threaten populations of slow-breeding beetles.

Animals↗
PubMed2002

Modelled impact of insecticide-contaminated dung on the abundance and distribution of dung fauna.

Deterministic models assessed the effects that contaminated dung from insecticide-treated cattle had on populations of three hypothetical species of dung fauna that dispersed randomly and could double their numbers every 1-28 weeks at low density. Insecticide was allowed to kill 2-98 % of adults and prevent 16-100% of breeding in pats produced immediately after cattle treatment, with toxicity declining to < 1% in pats produced 2-23 days later. Treatment intervals were 10-40 days. The modelled impact of insecticide was affected little by approximately four-fold variations in: length and density dependence of the attractive life span of pats, frequency of pat occupation by immature adults, distribution of pat toxicity during treatment interval, and changes in dispersal rates due to age and population density. Of greater importance were variations in: pat toxicity, treatment interval, frequency of pat occupation by breeding adults, density dependence of recruitment and death, natural adversity and mortality in dormancy, general rate of dispersal, and the size and shape of the area with treated cattle. Overall, it seemed that wide variations in the impact of contamination will occur in the field, but in many situations the risk to dung fauna can be substantial, especially for slow breeding beetles, and muscoids contacting insecticide on cattle. Risk extends outside the treated areas, for a distance equal to several daily displacements of the insects. Untreated refuges for species survival should be compact blocks at least 25 daily displacements wide.

Animals↗
PubMed1993

Development of baits for tsetse flies (Diptera: Glossinidae) in Zimbabwe.

Analysis of host-oriented behavior of tsetse flies, Glossina morsitans morsitans Westw. and G. pallidipes Austen, led to a 10- to 1,000-fold improvement in the cost effectiveness of baits for surveys and control. Baits now are used widely to replace air and ground broadcasting of insecticides. Principles of behavioral analysis are discussed, with emphasis on the need to: confirm that the measurements made are the measurements required; assess the probability of flies executing single specific actions in response to each component of the overall stimulus from baits; count not only the flies that do one thing, but also the number that do the alternative(s); and use objective sampling devices of measured efficiency. The relevance to research with other flies is considered. The need for new tools to study continuously the field behavior of individual flies is stressed.

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