The combination of Bacillus thuringiensis var israelensis and surface active monolayers for mosquito control
The combination of Bacillus thuringiensis var israelensis and surface active monolayers for mosquito control
Mosquito larvae ingesting delta-endotoxin crystals of Bacillus thuringiensis var. israelensis (Bti) died rapidly of toxicosis. This was complemented by a monomolecular film (monolayer) which killed both larvae and pupae by impairing their respiration. The combination did not reduce the surface pressure of the monolayer. Two outstanding beneficial effects resulted: 1. monolayer spread Bti a minimum of 2m over the water surface; monolayer remaining after the water surface had been covered formed a reservoir - a globule - that continued to spread and release Bti as it replenished biodegrading monolayer; 2. monolayer prevented rapid loss of toxin crystals from larval feeding zones by keeping Bti near the surface. A low cost liquid monolayer of high surface pressure was selected and mixed with a high activity Bti primary powder (LC50 0.004mg/1 with 3rd-instar Aedes aegypti). Because the powder sank in the monolayer during storage, a silicone gel (0.5%) was added giving a slow-to-settle, easy-to-mix suspension. A 1% Bti powder in liquid monolayer was used in the laboratory. In simulated tropical field conditions (tanks at 30oC), low dosages of less than 1 litre/hectare gave unexpectedly high mortalities after 4 days, as the cannibalistic larvae ate dead larvae in which the bacterium had sporulated and produced toxin. In field trials, the concentration of Bti in monolayer was increased to 3% for temperate conditions and 5% for tropical conditions, at a dosage rate of 3 litres of the mixture/hectare. Slow release of Bti enabled the interval before respray to be lengthened by x 1.7, possibly longer, compared with the intervals for either larvicide used alone. Despite great variation in the field, the effects demonstrated in the laboratory were confirmed. In practice the mixture in practice produced good mosquito control as part of a Malaria Research Control Project in Sri Lanka. Study of the sociological aspects revealed the great value of this new approach to malaria control, involving community participation, made possible by the notable safety of the two highly selective larvicides and their ability to spread after application by simple methods. Data collection continues with the objective of integrating all safe methods to achieve optimum control. (DX88273)
University of Southampton
Roberts, Gillian Mary
385427f7-d573-4eb5-8f59-e8c9512db7f7
1989
Roberts, Gillian Mary
385427f7-d573-4eb5-8f59-e8c9512db7f7
Roberts, Gillian Mary
(1989)
The combination of Bacillus thuringiensis var israelensis and surface active monolayers for mosquito control.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Mosquito larvae ingesting delta-endotoxin crystals of Bacillus thuringiensis var. israelensis (Bti) died rapidly of toxicosis. This was complemented by a monomolecular film (monolayer) which killed both larvae and pupae by impairing their respiration. The combination did not reduce the surface pressure of the monolayer. Two outstanding beneficial effects resulted: 1. monolayer spread Bti a minimum of 2m over the water surface; monolayer remaining after the water surface had been covered formed a reservoir - a globule - that continued to spread and release Bti as it replenished biodegrading monolayer; 2. monolayer prevented rapid loss of toxin crystals from larval feeding zones by keeping Bti near the surface. A low cost liquid monolayer of high surface pressure was selected and mixed with a high activity Bti primary powder (LC50 0.004mg/1 with 3rd-instar Aedes aegypti). Because the powder sank in the monolayer during storage, a silicone gel (0.5%) was added giving a slow-to-settle, easy-to-mix suspension. A 1% Bti powder in liquid monolayer was used in the laboratory. In simulated tropical field conditions (tanks at 30oC), low dosages of less than 1 litre/hectare gave unexpectedly high mortalities after 4 days, as the cannibalistic larvae ate dead larvae in which the bacterium had sporulated and produced toxin. In field trials, the concentration of Bti in monolayer was increased to 3% for temperate conditions and 5% for tropical conditions, at a dosage rate of 3 litres of the mixture/hectare. Slow release of Bti enabled the interval before respray to be lengthened by x 1.7, possibly longer, compared with the intervals for either larvicide used alone. Despite great variation in the field, the effects demonstrated in the laboratory were confirmed. In practice the mixture in practice produced good mosquito control as part of a Malaria Research Control Project in Sri Lanka. Study of the sociological aspects revealed the great value of this new approach to malaria control, involving community participation, made possible by the notable safety of the two highly selective larvicides and their ability to spread after application by simple methods. Data collection continues with the objective of integrating all safe methods to achieve optimum control. (DX88273)
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Published date: 1989
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Local EPrints ID: 461364
URI: http://eprints.soton.ac.uk/id/eprint/461364
PURE UUID: 874d6e78-3173-455d-94f6-ce2b697c0b74
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Date deposited: 04 Jul 2022 18:43
Last modified: 23 Jul 2022 01:08
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Author:
Gillian Mary Roberts
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