Studies on the development and survival of anopheles gambiae sensu stricto at various temperatures and relative humidities

Anopheles gambiae sensu stricto is the most efficient malaria vector in Africa. Recent advances in mapping the distribution of this vector have exploited the relationship between climatic factors and vector parameters such as growth, survival and reproduction. This work was designed to investigate the effect of temperature and humidity on the development and survival of the vector and to test the use of recently developed tools in describing its distribution. The development rate and survival of the aquatic stages of the vector were investigated at 16 constant temperatures. Adults were produced between 16 -34ºC with a peak development rate at 28ºC and peak number of adults at 22 -26ºC. Larvae survived for less than 7 days at 10º, 12º, 38 º, and 40ºC but for more than 5 weeks, at 14-18ºC without any development of adults. Laboratory models accurately predicted development times at natural breeding sites in The Gambia suggesting the applicability of the models to field situations. The survival and mortality rates of adult An. gambiae s.s. were monitored at combinations of temperatures from 0-45ºC at 5 intervals and 40%, 60%, 80% and 100% relative humidity. Survival was highest at 15-25ºC and 60-100% relative humidity. The temperature - larva development relation was used to produce a distribution map across Africa while climatic data from sites at which chromosomal forms of the insect have been found were used to map the distribution of the forms across West Africa. Climate is an important determinant of insect distribution and the use of climate and vector parameters in describing or predicting vector and disease distribution will provide a cheaper and less labour intensive tool than traditional methods

How malaria models relate temperature to malaria transmission

Background: It is well known that temperature has a major influence on the transmission of malaria parasites to their hosts. However, mathematical models do not always agree about the way in which temperature affects malaria transmission. Methods: In this study, we compared six temperature dependent mortality models for the malaria vector Anopheles gambiae sensu stricto. The evaluation is based on a comparison between the models, and observations from semi-field and laboratory settings. Results: Our results show how different mortality calculations can influence the predicted dynamics of malaria transmission. Conclusions: With global warming a reality, the projected changes in malaria transmission will depend on which mortality model is used to make such predictions

Additional file 1 of Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets

Supporting data showing the predominant species tested in the dose-ranging studies and resistance to pyrethroid insecticides in chlorfenapyr susceptibility tests

Additional file 3 of Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets

Raw bioassay results for: "Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets.

Additional file 2 of Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets

Raw bioassay results for: "Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets.

Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets.

BACKGROUND: Following agricultural use and large-scale distribution of insecticide-treated nets (ITNs), malaria vector resistance to pyrethroids is widespread in sub-Saharan Africa. Interceptor® G2 is a new dual active ingredient (AI) ITN treated with alpha-cypermethrin and chlorfenapyr for the control of pyrethroid-resistant malaria vectors. In anticipation of these new nets being more widely distributed, testing was conducted to develop a chlorfenapyr susceptibility bioassay protocol and gather susceptibility information. METHODS: Bottle bioassay tests were conducted using five concentrations of chlorfenapyr at 12.5, 25, 50, 100, and 200 µg AI/bottle in 10 countries in sub-Saharan Africa using 13,639 wild-collected Anopheles gambiae sensu lato (s.l.) (56 vector populations per dose) and 4,494 pyrethroid-susceptible insectary mosquitoes from 8 colonized strains. In parallel, susceptibility tests were conducted using a provisional discriminating concentration of 100 µg AI/bottle in 16 countries using 23,422 wild-collected, pyrethroid-resistant An. gambiae s.l. (259 vector populations). Exposure time was 60 min, with mortality recorded at 24, 48 and 72 h after exposure. RESULTS: Median mortality rates (up to 72 h after exposure) of insectary colony mosquitoes was 100% at all five concentrations tested, but the lowest dose to kill all mosquitoes tested was 50 µg AI/bottle. The median 72-h mortality of wild An. gambiae s.l. in 10 countries was 71.5, 90.5, 96.5, 100, and 100% at concentrations of 12.5, 25, 50, 100, and 200 µg AI/bottle, respectively. Log-probit analysis of the five concentrations tested determined that the LC95 of wild An. gambiae s.l. was 67.9 µg AI/bottle (95% CI: 48.8-119.5). The discriminating concentration of 203.8 µg AI/bottle (95% CI: 146-359) was calculated by multiplying the LC95 by three. However, the difference in mortality between 100 and 200 µg AI/bottle was minimal and large-scale testing using 100 µg AI/bottle with wild An. gambiae s.l. in 16 countries showed that this concentration was generally suitable, with a median mortality rate of 100% at 72 h. CONCLUSIONS: This study determined that 100 or 200 µg AI/bottle chlorfenapyr in bottle bioassays are suitable discriminating concentrations for monitoring susceptibility of wild An. gambiae s.l., using mortality recorded up to 72 h. Testing in 16 countries in sub-Saharan Africa demonstrated vector susceptibility to chlorfenapyr, including mosquitoes with multiple resistance mechanisms to pyrethroids