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Bart G J Knols - One of the best experts on this subject based on the ideXlab platform.
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the infectivity of the entomopathogenic fungus beauveria bassiana to insecticide resistant and susceptible Anopheles Arabiensis mosquitoes at two different temperatures
Malaria Journal, 2010Co-Authors: Basil D Brooke, R H Hunt, Lizette L Koekemoer, Bart G J Knols, Christophe K Kikankie, Marit Farenhorst, Matthew B ThomasAbstract:Background Control of the major African malaria vector species continues to rely extensively on the application of residual insecticides through indoor house spraying or bed net impregnation. Insecticide resistance is undermining the sustainability of these control strategies. Alternatives to the currently available conventional chemical insecticides are, therefore, urgently needed. Use of fungal pathogens as biopesticides is one such possibility. However, one of the challenges to the approach is the potential influence of varied environmental conditions and target species that could affect the efficacy of a biological 'active ingredient'. An initial investigation into this was carried out to assess the susceptibility of insecticide-susceptible and resistant laboratory strains and wild-collected Anopheles Arabiensis mosquitoes to infection with the fungus Beauveria bassiana under two different laboratory temperature regimes.
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spatial and temporal distribution of the malaria mosquito Anopheles Arabiensis in northern sudan influence of environmental factors and implications for vector control
Malaria Journal, 2009Co-Authors: Tellal B Ageep, Mark Q. Benedict, Jonathan Cox, Moawia M Hassan, Bart G J Knols, Colin A Malcolm, Ahmed Babiker, Badria El B SayedAbstract:Background Malaria is an important public health problem in northern Sudan, but little is known about the dynamics of its transmission. Given the characteristic low densities of Anopheles Arabiensis and the difficult terrain in this area, future vector control strategies are likely to be based on area-wide integrated pest management (AW-IPM) that may include the sterile insect technique (SIT). To support the planning and implementation of future AW-IPM activities, larval surveys were carried out to provide key data on spatial and seasonal dynamics of local vector populations.
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mating competitiveness of male Anopheles Arabiensis mosquitoes irradiated with a partially or fully sterilizing dose in small and large laboratory cages
Journal of Medical Entomology, 2008Co-Authors: M E H Helinski, Bart G J KnolsAbstract:Male mating competitiveness is a crucial parameter in many genetic control programs including the sterile insect technique (SIT). We evaluated competitiveness of male Anopheles Arabiensis Patton as a function of three experimental variables: (1) small or large cages for mating, (2) the effects of either a partially sterilizing (70 Gy) or fully sterilizing (120 Gy) dose, and (3) pupal or adult irradiation. Irradiated males competed for females with an equal number of unirradiated males. Competitiveness was determined by measuring hatch rates of individually laid egg batches. In small cages, pupal irradiation with the high dose resulted in the lowest competitiveness, whereas adult irradiation with the low dose gave the highest, with the latter males being equal in competitiveness to unirradiated males. In the large cage, reduced competitiveness of males irradiated in the pupal stage was more pronounced compared with the small cage; the males irradiated as adults at both doses performed similarly to unirradiated males. Unexpectedly, males irradiated with the high dose performed better in a large cage than in a small one. A high proportion of intermediate hatch rates was observed for eggs collected in the large cage experiments with males irradiated at the pupal stage. It is concluded that irradiation of adult An. Arabiensis with the partially sterilizing dose results in the highest competitiveness for both cage designs. Cage size affected competitiveness for some treatments; therefore, competitiveness determined in laboratory experiments must be confirmed by releases into simulated field conditions. The protocols described are readily transferable to evaluate male competitiveness for other genetic control techniques.
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radiation induced sterility for pupal and adult stages of the malaria mosquito Anopheles Arabiensis
Malaria Journal, 2006Co-Authors: Michelle E H Helinski, Bart G J Knols, Andrew G ParkerAbstract:Background: In the context of the Sterile Insect Technique (SIT), radiation-induced sterility in the malaria mosquito Anopheles Arabiensis Patton (Diptera: Culicidae) was studied. Male mosquitoes were exposed to gamma rays in the pupal or adult stage and dose-sterility curves were determined. Methods: Pupae were irradiated shortly before emergence (at 22–26 hrs of age), and adults <24 hrs post emergence. Doses tested ranged between 0 and 100 Gy. The effects of irradiation on adult emergence, male survival, induced sterility and insemination capability were evaluated. Emergence and insemination data were analysed using independent t-tests against the control. Correlation analyses were performed for insemination rate and dose and insemination and fecundity. Male survival was analysed using Kaplan-Meier survival analyses. Finally, the calculated residual fertility values were inverse-normal transformed and linear regression analyses performed. Results: Irradiation of pupae, for all doses tested, had no effect on adult emergence. Survival curves of males irradiated as pupae or adults were similar or even slightly higher than nonirradiated males. Overall, adults appeared to be slightly more susceptible to irradiation, although no significant differences for individual doses were observed. In the pupal stage, a significant negative correlation was found between insemination and dose, but the correlation-coefficient was associated with less than 25% of the total variation. A review of the literature indicated that An. Arabiensis is more radiation resistant than other anopheline mosquitoes. Conclusion: The optimal dose for male insects to be released in an SIT programme depends on their level of sterility and competitiveness. The use of semi-sterilizing doses to produce more competitive insects is discussed. The most convenient developmental stage for mosquito irradiation on a mass-scale are pupae, but pupal irradiation resulted in a lower insemination rate at the highest dose compared to adult irradiation. On the basis of this study, a suitable dose range that includes semi-sterilizing doses is identified to initiate competitiveness experiments for males irradiated at both developmental stages.
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radiation induced sterility for pupal and adult stages of the malaria mosquito Anopheles Arabiensis
Malaria Journal, 2006Co-Authors: Michelle E H Helinski, Bart G J Knols, Andrew G ParkerAbstract:In the context of the Sterile Insect Technique (SIT), radiation-induced sterility in the malaria mosquito Anopheles Arabiensis Patton (Diptera: Culicidae) was studied. Male mosquitoes were exposed to gamma rays in the pupal or adult stage and dose-sterility curves were determined. Pupae were irradiated shortly before emergence (at 22–26 hrs of age), and adults <24 hrs post emergence. Doses tested ranged between 0 and 100 Gy. The effects of irradiation on adult emergence, male survival, induced sterility and insemination capability were evaluated. Emergence and insemination data were analysed using independent t-tests against the control. Correlation analyses were performed for insemination rate and dose and insemination and fecundity. Male survival was analysed using Kaplan-Meier survival analyses. Finally, the calculated residual fertility values were inverse-normal transformed and linear regression analyses performed. Irradiation of pupae, for all doses tested, had no effect on adult emergence. Survival curves of males irradiated as pupae or adults were similar or even slightly higher than non-irradiated males. Overall, adults appeared to be slightly more susceptible to irradiation, although no significant differences for individual doses were observed. In the pupal stage, a significant negative correlation was found between insemination and dose, but the correlation-coefficient was associated with less than 25% of the total variation. A review of the literature indicated that An. Arabiensis is more radiation resistant than other anopheline mosquitoes. The optimal dose for male insects to be released in an SIT programme depends on their level of sterility and competitiveness. The use of semi-sterilizing doses to produce more competitive insects is discussed. The most convenient developmental stage for mosquito irradiation on a mass-scale are pupae, but pupal irradiation resulted in a lower insemination rate at the highest dose compared to adult irradiation. On the basis of this study, a suitable dose range that includes semi-sterilizing doses is identified to initiate competitiveness experiments for males irradiated at both developmental stages.
Jeremie R. L. Gilles - One of the best experts on this subject based on the ideXlab platform.
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optimization of mosquito egg production under mass rearing setting effects of cage volume blood meal source and adult population density for the malaria vector Anopheles Arabiensis
Malaria Journal, 2017Co-Authors: Wadaka Mamai, Hamidou Maiga, Nanwintoun S Bimbilesomda, Adel Barakat Ali, Jose G Juarez, Zaynab A I Muosa, Rosemary Susan Lees, Jeremie R. L. GillesAbstract:Background Anopheles Arabiensis is one of the major malaria vectors that put millions of people in endemic countries at risk. Mass-rearing of this mosquito is crucial for strategies that use sterile insect technique to suppress vector populations. The sterile insect technique (SIT) package for this mosquito species is being developed by the Insect Pest Control Subprogramme of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. To improve mass-rearing outcomes for An. Arabiensis, the question of whether the egg production by females would be affected by the size of the adult holding cages, the source of the blood meal and the total number of pupae that could be loaded into the cages was addressed and finally the impact of adding additional pupae to the cage daily to maintain adult numbers on egg productivity assessed.
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mating competitiveness of sterile genetic sexing strain males gama under laboratory and semi field conditions steps towards the use of the sterile insect technique to control the major malaria vector Anopheles Arabiensis in south africa
Parasites & Vectors, 2016Co-Authors: Givemore Munhenga, Jeremie R. L. Gilles, Basil D Brooke, Kobus Slabbert, A R Kemp, Leonard C Dandalo, Oliver R Wood, Leanne N Lobb, Dhanashree GovenderAbstract:Background Anopheles Arabiensis Patton is primarily responsible for malaria transmission in South Africa after successful suppression of other major vector species using indoor spraying of residual insecticides. Control of An. Arabiensis using current insecticide based approaches is proving difficult owing to the development of insecticide resistance, and variable feeding and resting behaviours. The use of the sterile insect technique as an area-wide integrated pest management system to supplement the control of An. Arabiensis was proposed for South Africa and is currently under investigation. The success of this technique is dependent on the ability of laboratory-reared sterile males to compete with wild males for mates. As part of the research and development of the SIT technique for use against An. Arabiensis in South Africa, radio-sensitivity and mating competitiveness of a local An. Arabiensis sexing strain were assessed.
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the Anopheles Arabiensis genetic sexing strain ano ipcl1 and its application potential for the sterile insect technique in integrated vector management programmes
Acta Tropica, 2015Co-Authors: Hanano Yamada, Kostas Bourtzis, Marc J B Vreysen, Wolfgang Tschirk, Dave D Chadee, Jeremie R. L. GillesAbstract:Abstract The Anopheles Arabiensis genetic sexing strain ANO IPCL1 was developed based on a dieldrin resistant mutation. The strain has been shown to be practical and reliable in terms of female elimination by dieldrin treatments at larval stages, but has provided some difficulties when treatments were applied at the egg stage. The high natural sterility of this strain has advantages and disadvantages in both mass rearing and the sterilization process. In addition, its recombination rate, although relatively low, poses a threat of strain deterioration if left unchecked in a mass-rearing setting. The males of the ANO IPCL1 have been shown to be equally competitive as lab-reared males of the wild-type Dongola strain, but competitiveness decreased by half when irradiated with 75 Gy – a dose conferring >98% sterility. More controversial issues surround the use of dieldrin – a highly persistent organochlorine that is known to bioaccumulate in the food chain. The prospective use of large volumes of dieldrin in a mass-rearing facility and the retention of its residues by the male mosquitoes makes the use of the strain in the context of the sterile insect technique against this vector highly questionable, and therefore its implementation at a large scale cannot be recommended.
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participation of irradiated Anopheles Arabiensis males in swarms following field release in sudan
Malaria Journal, 2014Co-Authors: Tellal B Ageep, Rosemary Susan Lees, Abdoulaye Diabate, Jeremie R. L. Gilles, David Damiens, Fayez T A Ahmed, Bashir Alsharif, Ayman Ahmed, Elwaleed H O Salih, Badria El B SayedAbstract:The success of the sterile insect technique (SIT) depends the release of large numbers of sterile males, which are able to compete for mates with the wild male population within the target area. Unfortunately, the processes of colonisation, mass production and irradiation may reduce the competitiveness of sterile males through genetic selection, loss of natural traits and somatic damage. In this context, the capacity of released sterile Anopheles Arabiensis males to survive, disperse and participate in swarms at occurring at varying distances from the release site was studied using mark-release-recapture (MRR) techniques. In order to assess their participation in swarms, irradiated and marked laboratory-reared male mosquitoes were released 50, 100 or 200 m from the known site of a large swarm on three consecutive nights. Males were collected from this large swarm on subsequent nights. Over the three days a total of 8,100 males were released. Mean distance travelled (MDT), daily probability of survival and estimated population size were calculated from the recapture data. An effect of male age at the time of release on these parameters was observed. Five per cent of the males released over three days were recaptured. In two-, three- and four-day-old males, MDT was 118, 178 and 170 m, and the daily survival probability 0.95, 0.90 and 0.75, respectively. From the recapture data on the first day following each release, the Lincoln index gives an estimation of 32,546 males in the natural population. Sterile An. Arabiensis males released into the field were able to find and participate in existing swarms, and possibly even initiate swarms. The survival probability decreased with the age of male on release but the swarm participation and the distance travelled by older males seemed higher than for younger males. The inclusion of a pre-release period may thus be beneficial to male competitiveness and increase the attractiveness of adult sexing techniques, such as blood spiking.
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An Inexpensive and Effective Larval Diet for Anopheles Arabiensis (Diptera: Culicidae): Eat Like a Horse, a Bird, or a Fish?
Journal of Medical Entomology, 2012Co-Authors: David Damiens, Marcel Wille, Mark Q. Benedict, Jeremie R. L. GillesAbstract:A successful sterile insect technique program depends upon mass production of good-quality sterile insects for release into a target area. Specifically, to control Anopheles Arabiensis Patton (Diptera: Culicidae) in a pilot area in northern Sudan, 1 million An. Arabiensis sterile males per day are needed. To reach this production objective, mosquito mass rearing is indispensable and larval diet, a key parameter for the production of healthy male mosquitoes, needs to be cost-effective. The Koi Floating Blend fish food, previously used at the Food and Agriculture Organization/International Atomic Energy Agency Insect Pest Control Laboratory for the routine rearing of the An. Arabiensis colony, is no longer available. The aim of this study was to find a cheap and effective substitute for the discontinued diet. Several candidate powdered diets that are commercially available were tested to determine the best diet. By using mixture experiment principles and response surface methodology, the combination of two components, bovine liver powder and tuna meal, showed the best results in terms of larval survival, developmental, rate and adult size. The addition of a vitamin mixture further improved the diet. These positive production results coupled with the relatively low cost of our blend demonstrated the possibility of its use for mass rearing purpose.
Basil D Brooke - One of the best experts on this subject based on the ideXlab platform.
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the contribution of gut bacteria to insecticide resistance and the life histories of the major malaria vector Anopheles Arabiensis diptera culicidae
Scientific Reports, 2019Co-Authors: Kirsten Barnard, Basil D Brooke, Shune V Oliver, Alexander C S N JeanrenaudAbstract:The gut microbiota of mosquitoes is a crucial determinant of their fitness. As such, the biology of the gut microbiota of Anopheles Arabiensis, a major malaria vector of Southern Africa, was investigated. Two laboratory strains of An. Arabiensis were used; SENN, an insecticide susceptible strain, and SENN-DDT, a resistant strain. The strains were supplemented with either non-commensal bacteria or antibiotics via a sucrose source to sterilize the gut. The strains were fed the broad-spectrum bactericidal antibiotic gentamicin, or a preferentially gram-positive bactericidal (vancomycin), gram-negative bactericidal (streptomycin) or broad-spectrum bacteriostatic (erythromycin), either by sugar supplementation or by artificially-spiked blood-meal. The effects on adult mosquito longevity and insecticide resistance phenotype were assessed. Bacteria from the midgut of both strains were characterised by MALDI-TOF mass spectroscopy. Bactericidal antibiotics increased longevity in SENN-DDT. Bacterial supplementation increased insecticide tolerance. Antibiotic supplementation via sugar decreased tolerance to the insecticides deltamethrin and malathion. Blood-supplemented vancomycin decreased insecticide resistance, while gentamicin and streptomycin increased resistance. SENN showed a greater gut bacterial diversity than SENN-DDT, with both strains dominated by Gram-negative bacteria. This study suggests a crucial role for bacteria in An. Arabiensis life history, and that gut microflora play variable roles in insecticide resistant and susceptible mosquitoes.
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mating competitiveness of sterile genetic sexing strain males gama under laboratory and semi field conditions steps towards the use of the sterile insect technique to control the major malaria vector Anopheles Arabiensis in south africa
Parasites & Vectors, 2016Co-Authors: Givemore Munhenga, Jeremie R. L. Gilles, Basil D Brooke, Kobus Slabbert, A R Kemp, Leonard C Dandalo, Oliver R Wood, Leanne N Lobb, Dhanashree GovenderAbstract:Background Anopheles Arabiensis Patton is primarily responsible for malaria transmission in South Africa after successful suppression of other major vector species using indoor spraying of residual insecticides. Control of An. Arabiensis using current insecticide based approaches is proving difficult owing to the development of insecticide resistance, and variable feeding and resting behaviours. The use of the sterile insect technique as an area-wide integrated pest management system to supplement the control of An. Arabiensis was proposed for South Africa and is currently under investigation. The success of this technique is dependent on the ability of laboratory-reared sterile males to compete with wild males for mates. As part of the research and development of the SIT technique for use against An. Arabiensis in South Africa, radio-sensitivity and mating competitiveness of a local An. Arabiensis sexing strain were assessed.
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the effect of multiple blood feeding on the longevity and insecticide resistant phenotype in the major malaria vector Anopheles Arabiensis diptera culicidae
Parasites & Vectors, 2014Co-Authors: Shune V Oliver, Basil D BrookeAbstract:Background Anopheles Arabiensis is a major malaria vector in Africa. Adult females are likely to imbibe multiple blood meals during their lifetime. This results in regular exposure to potential toxins and blood-meal induced oxidative stress. Defence responses to these stressors may affect other factors of epidemiological significance, such as insecticide resistance and longevity. The aims of this study were to examine the effect of multiple blood-feeding on insecticide tolerance/resistance with increasing age, to assess the underlying biochemical mechanisms for the responses recorded, and to assess the effect of multiple blood-feeding on the life histories of adult females drawn from insecticide resistant and susceptible laboratory reared An. Arabiensis.
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the effect of larval nutritional deprivation on the life history and ddt resistance phenotype in laboratory strains of the malaria vector Anopheles Arabiensis
Malaria Journal, 2013Co-Authors: Shune V Oliver, Basil D BrookeAbstract:Anopheles Arabiensis is a major malaria vector in Africa. It thrives in agricultural areas and has been associated with increased malaria incidence in areas under rice and maize cultivation. This effect may be due to increased adult size and abundance as a consequence of optimal larval nutrition. The aim of this study was to examine the effect of larval nutrition on the life history and expression of insecticide resistance in adults of laboratory reared An. Arabiensis. Larvae drawn from an insecticide susceptible An. Arabiensis strain (SENN) as well as a DDT-resistant strain (SENN-DDT) were subjected to three fasting regimes: 1 mg of food per larva offered once per day, once every second day and once every third day. Control cohorts included larvae offered 1 mg food thrice per day. The rate of larval development was compared between matched cohorts from each strain as well as between fasted larvae and their respective controls. The expression of DDT resistance/tolerance in adults was compared between the starved cohorts and their controls by strain. Factors potentially affecting variation in DDT resistance/tolerance were examined including: adult body size (wing length), knock-down resistance (kdr) status and levels of detoxification enzyme activity. Anopheles Arabiensis larval development is prolonged by nutrient deprivation and adults that eclose from starved larvae are smaller and less tolerant to DDT intoxication. This effect on DDT tolerance in adults is also associated with reduced detoxification enzyme activity. Conversely, well fed larvae develop comparatively quickly into large, more DDT tolerant (SENN) or resistant (SENN-DDT) adults. This is important in those instances where cereal farming is associated with increased An. Arabiensis transmitted malaria incidence, because large adult females with high teneral reserves and decreased susceptibility to insecticide intoxication may also prove to be more efficient malaria vectors. In general, larval nutrient deprivation in An. Arabiensis has important implications for subsequent adults in terms of their size and relative insecticide susceptibility, which may in turn impact on their malaria vector capacity in areas where insecticide based control measures are in place.
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insecticide resistance in Anopheles Arabiensis diptera culicidae from villages in central northern and south west ethiopia and detection of kdr mutation
Parasites & Vectors, 2010Co-Authors: Meshesha Balkew, Teshome Gebremichael, Basil D Brooke, Lizette L Koekemoer, Muntaser E Ibrahim, Howard Engers, Abraham Aseffa, Ibrahim M ElhassenAbstract:Background Anopheles Arabiensis is the major vector of malaria in Ethiopia. Malaria vector control in Ethiopia is based on selective indoor residual spraying using DDT, distribution of long lasting insecticide treated nets and environmental management of larval breeding habitats. DDT and pyrethroid insecticides are neurotoxins and have a similar mode of action on the sodium ion channel of insects. It was therefore necessary to verify the insecticide susceptibility status of An. Arabiensis, to better understand the status of cross-resistance between DDT and the pyrethroids in this species as well as to detect a resistant gene.
Maureen Coetzee - One of the best experts on this subject based on the ideXlab platform.
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desiccation tolerance as a function of age sex humidity and temperature in adults of the african malaria vectors Anopheles Arabiensis and Anopheles funestus
The Journal of Experimental Biology, 2014Co-Authors: Maureen Coetzee, Candice L Lyons, John S Terblanche, Steven L ChownAbstract:Adult mosquito survival is strongly temperature and moisture dependent. Few studies have investigated the interacting effects of these variables on adult survival and how this differs among the sexes and with age, despite the importance of such information for population dynamic models. For these reasons, the desiccation tolerance of Anopheles Arabiensis Patton and Anopheles funestus Giles males and females of three different ages was assessed under three combinations of temperature and humidity. Females were more desiccation tolerant than males, surviving for longer periods than males under all experimental conditions. In addition, younger adults were more tolerant of desiccation than older groups. Both species showed reduced water loss rate (WLR) as the primary mechanism by which they tolerate desiccation. Although A. Arabiensis is often considered to be the more arid-adapted of the two species, it showed lower survival times and higher WLR than A. funestus. The current information could improve population dynamic models of these vectors, given that adult survival information for such models is relatively sparse.
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insecticide resistance in Anopheles Arabiensis in sudan temporal trends and underlying mechanisms
Parasites & Vectors, 2014Co-Authors: Hiba Abdalla, Craig S Wilding, Luisa Nardini, Patricia Pignatelli, Lizette L Koekemoer, Hilary Ranson, Maureen CoetzeeAbstract:Malaria vector control in Sudan relies mainly on indoor residual spraying (IRS) and the use of long lasting insecticide treated bed nets (LLINs). Monitoring insecticide resistance in the main Sudanese malaria vector, Anopheles Arabiensis, is essential for planning and implementing an effective vector control program in this country. WHO susceptibility tests were used to monitor resistance to insecticides from all four WHO-approved classes of insecticide at four sentinel sites in Gezira state over a three year period. Insecticide resistance mechanisms were studied using PCR and microarray analyses. WHO susceptibility tests showed that Anopheles Arabiensis from all sites were fully susceptible to bendiocarb and fenitrothion for the duration of the study (2008–2011). However, resistance to DDT and pyrethroids was detected at three sites, with strong seasonal variations evident at all sites. The 1014 F kdr allele was significantly associated with resistance to pyrethroids and DDT (P 7 in allelic tests). The 1014S allele was not detected in any of the populations tested. Microarray analysis of the permethrin-resistant population of An. Arabiensis from Wad Medani identified a number of metabolic genes that were significantly over-transcribed in the field-collected resistant samples when compared to the susceptible Sudanese An. Arabiensis Dongola strain. These included CYP6M2 and CYP6P3, two genes previously implicated in pyrethroid resistance in Anopheles gambiae s.s, and the epsilon-class glutathione-S-transferase, GSTe4. These data suggest that both target-site mechanisms and metabolic mechanisms play an important role in conferring pyrethroid resistance in An. Arabiensis from Sudan. Identification in An. Arabiensis of candidate loci that have been implicated in the resistance phenotype in An. gambiae requires further investigation to confirm the role of these genes.
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stable and fluctuating temperature effects on the development rate and survival of two malaria vectors Anopheles Arabiensis and Anopheles funestus
Parasites & Vectors, 2013Co-Authors: Maureen Coetzee, Candice L Lyons, Steven L ChownAbstract:Background: Understanding the biology of malaria vector mosquitoes is crucial to understanding many aspects of the disease, including control and future outcomes. The development rates and survival of two Afrotropical malaria vectors, Anopheles Arabiensis and Anopheles funestus, are investigated here under conditions of constant and fluctuating temperatures. These data can provide a good starting point for modelling population level consequences of temperature change associated with climate change. For comparative purposes, these data were considered explicitly in the context of those available for the third African malaria vector, Anopheles gambiae. Methods: Twenty five replicates of 20–30 eggs were placed at nine constant and two fluctuating temperatures for development rate experiments and survival estimates. Various developmental parameters were estimated from the data, using standard approaches. Results: Lower development threshold (LDT) for both species was estimated at 13-14°C. Anopheles Arabiensis developed consistently faster than An. funestus. Optimum temperature (Topt) and development rate at this temperature (μmax) differed significantly between species for overall development and larval development. However, Topt and μmax for pupal development did not differ significantly between species. Development rate and survival of An. funestus was negatively influenced by fluctuating temperatures. By contrast, development rate of An. Arabiensis at fluctuating temperatures either did not differ from constant temperatures or was significantly faster. Survival of this species declined by c. 10% at the 15°C to 35°C fluctuating temperature regime, but was not significantly different between the constant 25°C and the fluctuating 20°C to 30°C treatment. By comparison, previous data for An. gambiae indicated fastest development at a constant temperature of 28°C and highest survival at 24°C. Conclusions: The three most important African malaria vectors all differ significantly in development rates and survival under different temperature treatments, in keeping with known distribution data, though differences among M and S molecular forms of An. gambiae likely complicate the picture. Increasing temperatures associated with climate change favour all three species, but fluctuations in temperatures are detrimental to An. funestus and may also be for An. gambiae. This may have significant implications for disease burden in areas where each species is the main malaria vector.
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detoxification enzymes associated with insecticide resistance in laboratory strains of Anopheles Arabiensis of different geographic origin
Parasites & Vectors, 2012Co-Authors: Luisa Nardini, Hilary Ranson, Maureen Coetzee, Riann N Christian, Nanette Coetzer, Lizette L KoekemoerAbstract:The use of insecticides to control malaria vectors is essential to reduce the prevalence of malaria and as a result, the development of insecticide resistance in vector populations is of major concern. Anopheles Arabiensis is one of the main African malaria vectors and insecticide resistance in this species has been reported in a number of countries. The aim of this study was to investigate the detoxification enzymes that are involved in An. Arabiensis resistance to DDT and pyrethroids. The detoxification enzyme profiles were compared between two DDT selected, insecticide resistant strains of An. Arabiensis, one from South Africa and one from Sudan, using the An. gambiae detoxification chip, a boutique microarray based on the major classes of enzymes associated with metabolism and detoxification of insecticides. Synergist assays were performed in order to clarify the roles of over-transcribed detoxification genes in the observed resistance phenotypes. In addition, the presence of kdr mutations in the colonies under investigation was determined. The microarray data identifies several genes over-transcribed in the insecticide selected South African strain, while in the Sudanese population, only one gene, CYP9L1, was found to be over-transcribed. The outcome of the synergist experiments indicate that the over-transcription of detoxification enzymes is linked to deltamethrin resistance, while DDT and permethrin resistance are mainly associated with the presence of the L1014F kdr mutation. These data emphasise the complexity associated with resistance phenotypes and suggest that specific insecticide resistance mechanisms cannot be extrapolated to different vector populations of the same species.
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pyrethroid resistance in a major african malaria vector Anopheles Arabiensis from mamfene northern kwazulu natal south africa
South African Journal of Science, 2010Co-Authors: Joel C Mouatcho, Givemore Munhenga, Basil D Brooke, Maureen Coetzee, K Hargreaves, Lizette L KoekemoerAbstract:A population of Anopheles Arabiensis, a major malaria vector in South Africa, was collected during 2005 from inside sprayed houses in Mamfene, northern KwaZulu-Natal, South Africa, using window exit traps. None of these specimens (n = 300 females) was found to be infected with Plasmodium falciparum. Insecticide susceptibility assays on 2–3 day old F1 progeny using WHO susceptibility kits revealed 100% susceptibility to bendiocarb, resistance to deltamethrin (95.91%) was suspected, while resistance to permethrin (78.05%) was confirmed. The knockdown resistant (kdr) genotype was not found in the surviving mosquitoes. Biochemical analysis using enzyme assays showed elevated levels of monooxygenase that correlated with the permethrin bioassay data. While elevated levels of non-specific esterase were found in some families (11/12 for α- and 6/12 for -esterases), the data did not show any correlation with the permethrin bioassay. Analysis of permethrin and bendiocarb tolerant lines, selected in the laboratory to characterise biochemical resistance profiles, showed increased levels of non-specific esterase and monooxygenase activity in the case of the permethrin-selected cohorts, and elevated glutathione S-trans
Shune V Oliver - One of the best experts on this subject based on the ideXlab platform.
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the contribution of gut bacteria to insecticide resistance and the life histories of the major malaria vector Anopheles Arabiensis diptera culicidae
Scientific Reports, 2019Co-Authors: Kirsten Barnard, Basil D Brooke, Shune V Oliver, Alexander C S N JeanrenaudAbstract:The gut microbiota of mosquitoes is a crucial determinant of their fitness. As such, the biology of the gut microbiota of Anopheles Arabiensis, a major malaria vector of Southern Africa, was investigated. Two laboratory strains of An. Arabiensis were used; SENN, an insecticide susceptible strain, and SENN-DDT, a resistant strain. The strains were supplemented with either non-commensal bacteria or antibiotics via a sucrose source to sterilize the gut. The strains were fed the broad-spectrum bactericidal antibiotic gentamicin, or a preferentially gram-positive bactericidal (vancomycin), gram-negative bactericidal (streptomycin) or broad-spectrum bacteriostatic (erythromycin), either by sugar supplementation or by artificially-spiked blood-meal. The effects on adult mosquito longevity and insecticide resistance phenotype were assessed. Bacteria from the midgut of both strains were characterised by MALDI-TOF mass spectroscopy. Bactericidal antibiotics increased longevity in SENN-DDT. Bacterial supplementation increased insecticide tolerance. Antibiotic supplementation via sugar decreased tolerance to the insecticides deltamethrin and malathion. Blood-supplemented vancomycin decreased insecticide resistance, while gentamicin and streptomycin increased resistance. SENN showed a greater gut bacterial diversity than SENN-DDT, with both strains dominated by Gram-negative bacteria. This study suggests a crucial role for bacteria in An. Arabiensis life history, and that gut microflora play variable roles in insecticide resistant and susceptible mosquitoes.
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the impact of temperature on insecticide toxicity against the malaria vectors Anopheles Arabiensis and Anopheles funestus
Malaria Journal, 2018Co-Authors: Katey D Glunt, R H Hunt, Shune V Oliver, Krijn P PaaijmansAbstract:It is anticipated that malaria elimination efforts in Africa will be hampered by increasing resistance to the limited arsenal of insecticides approved for use in public health. However, insecticide susceptibility status of vector populations evaluated under standard insectary test conditions can give a false picture of the threat, as the thermal environment in which the insect and insecticide interact plays a significant role in insecticide toxicity. The effect of temperature on the expression of the standard WHO insecticide resistance phenotype was examined using Anopheles Arabiensis and Anopheles funestus strains: a susceptible strain and the derived resistant strain, selected in the laboratory for resistance to DDT or pyrethroids. The susceptibility of mosquitoes to the pyrethroid deltamethrin or the carbamate bendiocarb was assessed at 18, 25 or 30 °C. The ability of the pyrethroid synergist piperonyl-butoxide (PBO) to restore pyrethroid susceptibility was also assessed at these temperatures. Temperature impacted the toxicity of deltamethrin and bendiocarb. Although the resistant An. funestus strain was uniformly resistant to deltamethrin across temperatures, increasing temperature increased the resistance of the susceptible An. Arabiensis strain. Against susceptible An. funestus and resistant An. Arabiensis females, deltamethrin exposure at temperatures both lower and higher than standard insectary conditions increased mortality. PBO exposure completely restored deltamethrin susceptibility at all temperatures. Bendiocarb displayed a consistently positive temperature coefficient against both susceptible and resistant An. funestus strains, with survival increasing as temperature increased. Environmental temperature has a marked effect on the efficacy of insecticides used in public health against important African malaria vectors. Caution must be exercised when drawing conclusions about a chemical’s efficacy from laboratory assays performed at only one temperature, as phenotypic resistance can vary significantly even over a temperature range that could be experienced by mosquitoes in the field during a single day. Similarly, it might be inappropriate to assume equal efficacy of a control tool over a geographic area where local conditions vary drastically. Additional studies into the effects of temperature on the efficacy of insecticide-based interventions under field conditions are warranted.
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The impact of temperature on insecticide toxicity against the malaria vectors Anopheles Arabiensis and Anopheles funestus
BMC, 2018Co-Authors: Katey D Glunt, Shune V Oliver, Richard H. Hunt, Krijn P PaaijmansAbstract:Abstract Background It is anticipated that malaria elimination efforts in Africa will be hampered by increasing resistance to the limited arsenal of insecticides approved for use in public health. However, insecticide susceptibility status of vector populations evaluated under standard insectary test conditions can give a false picture of the threat, as the thermal environment in which the insect and insecticide interact plays a significant role in insecticide toxicity. Methods The effect of temperature on the expression of the standard WHO insecticide resistance phenotype was examined using Anopheles Arabiensis and Anopheles funestus strains: a susceptible strain and the derived resistant strain, selected in the laboratory for resistance to DDT or pyrethroids. The susceptibility of mosquitoes to the pyrethroid deltamethrin or the carbamate bendiocarb was assessed at 18, 25 or 30 °C. The ability of the pyrethroid synergist piperonyl-butoxide (PBO) to restore pyrethroid susceptibility was also assessed at these temperatures. Results Temperature impacted the toxicity of deltamethrin and bendiocarb. Although the resistant An. funestus strain was uniformly resistant to deltamethrin across temperatures, increasing temperature increased the resistance of the susceptible An. Arabiensis strain. Against susceptible An. funestus and resistant An. Arabiensis females, deltamethrin exposure at temperatures both lower and higher than standard insectary conditions increased mortality. PBO exposure completely restored deltamethrin susceptibility at all temperatures. Bendiocarb displayed a consistently positive temperature coefficient against both susceptible and resistant An. funestus strains, with survival increasing as temperature increased. Conclusions Environmental temperature has a marked effect on the efficacy of insecticides used in public health against important African malaria vectors. Caution must be exercised when drawing conclusions about a chemical’s efficacy from laboratory assays performed at only one temperature, as phenotypic resistance can vary significantly even over a temperature range that could be experienced by mosquitoes in the field during a single day. Similarly, it might be inappropriate to assume equal efficacy of a control tool over a geographic area where local conditions vary drastically. Additional studies into the effects of temperature on the efficacy of insecticide-based interventions under field conditions are warranted
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the effect of multiple blood feeding on the longevity and insecticide resistant phenotype in the major malaria vector Anopheles Arabiensis diptera culicidae
Parasites & Vectors, 2014Co-Authors: Shune V Oliver, Basil D BrookeAbstract:Background Anopheles Arabiensis is a major malaria vector in Africa. Adult females are likely to imbibe multiple blood meals during their lifetime. This results in regular exposure to potential toxins and blood-meal induced oxidative stress. Defence responses to these stressors may affect other factors of epidemiological significance, such as insecticide resistance and longevity. The aims of this study were to examine the effect of multiple blood-feeding on insecticide tolerance/resistance with increasing age, to assess the underlying biochemical mechanisms for the responses recorded, and to assess the effect of multiple blood-feeding on the life histories of adult females drawn from insecticide resistant and susceptible laboratory reared An. Arabiensis.
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the effect of larval nutritional deprivation on the life history and ddt resistance phenotype in laboratory strains of the malaria vector Anopheles Arabiensis
Malaria Journal, 2013Co-Authors: Shune V Oliver, Basil D BrookeAbstract:Anopheles Arabiensis is a major malaria vector in Africa. It thrives in agricultural areas and has been associated with increased malaria incidence in areas under rice and maize cultivation. This effect may be due to increased adult size and abundance as a consequence of optimal larval nutrition. The aim of this study was to examine the effect of larval nutrition on the life history and expression of insecticide resistance in adults of laboratory reared An. Arabiensis. Larvae drawn from an insecticide susceptible An. Arabiensis strain (SENN) as well as a DDT-resistant strain (SENN-DDT) were subjected to three fasting regimes: 1 mg of food per larva offered once per day, once every second day and once every third day. Control cohorts included larvae offered 1 mg food thrice per day. The rate of larval development was compared between matched cohorts from each strain as well as between fasted larvae and their respective controls. The expression of DDT resistance/tolerance in adults was compared between the starved cohorts and their controls by strain. Factors potentially affecting variation in DDT resistance/tolerance were examined including: adult body size (wing length), knock-down resistance (kdr) status and levels of detoxification enzyme activity. Anopheles Arabiensis larval development is prolonged by nutrient deprivation and adults that eclose from starved larvae are smaller and less tolerant to DDT intoxication. This effect on DDT tolerance in adults is also associated with reduced detoxification enzyme activity. Conversely, well fed larvae develop comparatively quickly into large, more DDT tolerant (SENN) or resistant (SENN-DDT) adults. This is important in those instances where cereal farming is associated with increased An. Arabiensis transmitted malaria incidence, because large adult females with high teneral reserves and decreased susceptibility to insecticide intoxication may also prove to be more efficient malaria vectors. In general, larval nutrient deprivation in An. Arabiensis has important implications for subsequent adults in terms of their size and relative insecticide susceptibility, which may in turn impact on their malaria vector capacity in areas where insecticide based control measures are in place.