Experimental hut comparisons of nets treated with carbamate or pyrethroid insecticides, washed or unwashed, against pyrethroid-resistant mosquitoes.

The efficacy against mosquitoes (Diptera: Culicidae) of a bednet treated with carbamate insecticide [carbosulfan capsule suspension (CS) 200 mg/m(2)] was compared with four types of pyrethroid-treated nets in veranda-trap huts at Yaokoffikro near Bouaké, Côte d'Ivoire, where the malaria vector Anopheles gambiae Giles carries the kdr gene (conferring pyrethroid resistance) at high frequency and Culex quinquefasciatus Say is also pyrethroid resistant. Pyrethroids compared were lambdacyhalothrin CS 18 mg/m(2), alphacypermethrin water dispersible granules (WG) 20 mg/m(2), deltamethrin 50 mg/m(2) (Permanet) and permethrin emulsifiable concentrate (EC) 500 mg/m(2). Insecticidal power and personal protection from mosquito bites were assessed before and after the nets were used for 8 months and hand washed five times in cold soapy water. Before washing, all treatments except permethrin significantly reduced blood-feeding and all had significant insecticidal activity against An. gambiae. The carbosulfan net gave significantly higher killing of An. gambiae than all pyrethroid treatments except the Permanet. Against Culex spp., carbosulfan was more insecticidal and gave a significantly better protective effect than any of the pyrethroid treatments. After washing, treated nets retained various degrees of efficacy against both mosquito genera - but least for the carbosulfan net. Washed nets with three types of pyrethroid treatment (alphacypermethrin, lambdacyhalothrin, permethrin) gave significantly higher mortality rates of Culex than in huts with the same pyrethroid-treated nets before washing. After five washes, the Permanet, which is sold as a long-lasting insecticidal product, performed no better than the other nets in our experimental conditions

Combining indoor residual spraying with chlorfenapyr and long-lasting insecticidal bed nets for improved control of pyrethroid-resistant Anopheles gambiae: an experimental hut trial in Benin.

BACKGROUND: Neither indoor residual spraying (IRS) nor long-lasting insecticidal nets (LLINs) are able to fully interrupt transmission in holoendemic Africa as single interventions. The combining of IRS and LLINs presents an opportunity for improved control and management of pyrethroid resistance through the simultaneous presentation of unrelated insecticides. METHOD: Chlorfenapyr IRS and a pyrethroid-impregnated polyester LLIN (WHO approved) were tested separately and together in experimental huts in southern Benin against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus. The bed nets were deliberately holed with either six or 80 holes to examine the effect of increasing wear and tear on protectiveness. Anopheles gambiae were genotyped for the kdr gene to assess the combination's potential to prevent the selection of pyrethroid resistance. RESULTS: The frequency of kdr was 84%. The overall mortality rates of An. gambiae were 37% and 49% with the six-hole and 80-hole LLINs, respectively, and reached 57% with chlorfenapyr IRS. Overall mortality rates were significantly higher with the combination treatments (82-83%) than with the LLIN or IRS individual treatments. Blood feeding (mosquito biting) rates were lowest with the 6-hole LLIN (12%), intermediate with the 80-hole LLIN (32%) and highest with untreated nets (56% with the 6-hole and 54% with the 80-hole nets). Blood feeding (biting) rates and repellency of mosquitoes with the combination of LLIN and chlorfenapyr IRS showed significant improvement compared to the IRS treatment but did not differ from the LLIN treatments indicating that the LLINs were the primary agents of personal protection. The combination killed significantly higher proportions of Cx. quinquefasciatus (51%, 41%) than the LLIN (15%, 13%) or IRS (32%) treatments. CONCLUSION: The chlorfenapyr IRS component was largely responsible for controlling pyrethroid-resistant mosquitoes and the LLIN component was largely responsible for blood feeding inhibition and personal protection. Together, the combination shows potential to provide additional levels of transmission control and personal protection against pyrethroid-resistant mosquitoes, thereby justifying the additional resources required. Chlorfenapyr has potential to manage pyrethroid resistance in the context of an expanding LLIN/IRS strategy

Measurement of overall insecticidal effects in experimental hut trials

BACKGROUND: The 'overall insecticidal effect' is a key measure used to evaluate public health pesticides for indoor use in experimental hut trials. It depends on the proportion of mosquitoes that are killed out of those that enter the treated hut, intrinsic mortality in the control hut, and the ratio of mosquitoes entering the treatment hut to those entering the control hut. This paper critically examines the way the effect is defined, and discusses how it can be used to infer effectiveness of intervention programmes. FINDINGS: The overall insecticidal effect, as defined by the World Health Organization in 2006, can be negative when deterrence from entering the treated hut is high, even if all mosquitoes that enter are killed, wrongly suggesting that the insecticide enhances mosquito survival. Also in the absence of deterrence, even if the insecticide kills all mosquitoes in the treatment hut, the insecticidal effect is less than 100%, unless intrinsic mortality is nil. A proposed alternative definition for the measurement of the overall insecticidal effect has the desirable range of 0 to 1 (100%), provided mortality among non-repelled mosquitoes in the treated hut is less than the corresponding mortality in the control hut. This definition can be built upon to formulate the coverage-dependent insecticidal effectiveness of an intervention programme. Coverage-dependent population protection against feeding can be formulated similarly. CONCLUSIONS: This paper shows that the 2006 recommended quantity for measuring the overall insecticidal effect is problematic, and proposes an alternative quantity with more desirable propertie

Insecticide resistance in the West African malaria vector Anopheles gambiae and investigation of alternative tools for its delay

There is a current policy to eliminate malaria in the African continent. Pyrethroid-incorporated Long Lasting Insecticidal Nets (LLINs) and/or Indoor Residual Spraying (IRS) are the chemical weapons being deployed to achieve that goal. Rather worryingly, resistance to pyrethroids is well documented in the major vectors of malaria in Africa, and could decimate the contribution that vector control can make to any successful elimination agenda over the next decade. DDT (Dichlorodiphenyltrichloroethane) for IRS is cost effective but undesirable because of its environmental impact. There is a need to identify pyrethroid resistance mechanisms in the areas being scaled up, evaluate their direct impact on the efficacy of these tools and identify novel tools that might have potential as alternatives to pyrethroids and DDT for net or indoor residual treatments. This thesis reports that pyrethroid, organophosphate (Ops) & carbamate resistance is present in the Mopti (M) and Savanah (S) molecular forms of the major vector of malaria, Anopheles gambiae, in two West African countries, Benin and Ivory Coast where LLINs are currently being deployed,. Mechanisms for pyrethroids include elevated oxidase activities and the knock down resistance (kdr) gene at high frequency (>80%) whereas an insensitive acetylcholinesterase conferred Ops and carbamate resistance. Experimental hut tests in Southern Benin showed that the efficacy of Insecticide Treated Net (ITN) and IRS with the pyrethroid lambdacyalothrin was seriously compromised by pyrethroid resistance in the M form of An. gambiae, as opposed to the North where there is no record of pyrethroid resistance. This type of pyrethroid resistance, now spreading through West African populations of the M molecular form of An. gambiae, appears to have major operational significance in other areas such as Bioko, Niger and Burkina Faso. The alternative candidate insecticides, indoxacarb (an oxadiazine), chlorfenapy (a pyrrole) and chlorpyrifos methyl (an organophosphate) were evaluated, in the laboratory and/or in the field. In the laboratory, indoxacarb and chlorfenapyr on netting were more toxic than permethrin over the same dosage range (100-500mg/m2). Toxic activity was rather slow and bloodfeeding of mosquitoes was uninhibited in the presence of either insecticide. The experimental hut tests conducted in Southern Benin indicated that chlorfenapyr has high potential for IRS, killing 82.9% of pyrethroid resistant An. gambiae and 69% of Culex quinquefasciatus. Likewise, IRS with chlorpyrifos methyl CS (Capsule Suspension) was very efficacious at the same site in Benin. It killed 95.5% of pyrethroid resistant An. gambiae that entered a hut and showed activity on walls that lasted for more than 9 months without significant decay. If applied at high coverage, chlorpyrifos methyl CS should show higher, more-sustained levels of malaria transmission control than that achievable with DDT or pyrethroids. The feasibility of applying synthetic insect repellents on bednets (RTNs) to control insecticide resistant mosquitoes was explored in the second country, Ivory Coast. The results of tests done in experimental huts showed that formulations of volatile DEET (N,N-diethyl-3-methylbenzamide) and ethyl butylacetylaminopropionate (IR3535) on nets reduced bloodfeeding and the entry rate of mosquitoes into huts. An unexpected result was the 69-76% mortality of An. gambiae and 51-61% mortality of Cx. quinquefasciatus in huts containing RTNs. The DEET-based product provided better efficacy but was short-lived. Further treatment of netting with a formulation of DEET in which the repellent is gradually released from a capsule that binds the repellent strongly, showed that the formulation repels, inhibits blood-feeding and kills mosquitoes for a period of at least 6 months under laboratory conditions. Application of repellents to nets warrants further investigation as well as their development as alternatives to pyrethroids. Because it will not be possible to go for malaria elimination with the current tools, based on pyrethroids only, the results obtained with chlorfenapyr, indoxacarb and chlorpyrifos methyl should encourage further studies aiming at supplementing pyrethroids for vector control in areas where malaria mosquitoes are resistant to pyrethroids. <br/

Efficacy of mosquito nets treated with insecticide mixtures or mosaics against insecticide resistant Anopheles gambiae and Culex quinquefasciatus (Diptera: Culicidae) in Côte d'Ivoire

Only pyrethroid insecticides have so far been recommended for the treatment of mosquito nets for malaria control. Increasing resistance of malaria vectors to pyrethroids threatens to reduce the potency of this important method of vector control. Among the strategies proposed for resistance management is to use a pyrethroid and a non-pyrethroid insecticide in combination on the same mosquito net, either separately or as a mixture. Mixtures are particularly promising if there is potentiation between the two insecticides as this would make it possible to lower the dosage of each, as has been demonstrated under laboratory conditions for a mixture of bifenthrin (pyrethroid) and carbosulfan (carbamate). The effect of these types of treatment were compared in experimental huts on wild populations of Anopheles gambiae Giles and the nuisance mosquito Culex quinquefasciatus Say, both of which are multi-resistant. Four treatments were evaluated in experimental huts over six months: the recommended dosage of 50 mg m−2 bifenthrin, 300 mg m−2 carbosulfan, a mosaic of 300 mg m−2 carbosulfan on the ceiling and 50 mg m−2 bifenthrin on the sides, and a mixture of 6.25 mg m−2 carbosulfan and 25 mg m−2 bifenthrin. The mixture and mosaic treatments did not differ significantly in effectiveness from carbosulfan and bifenthrin alone against anophelines in terms of deterrency, induced exophily, blood feeding inhibition and overall mortality, but were more effective than in earlier tests with deltamethrin. These results are considered encouraging, as the combination of different classes of insecticides might be a potential tool for resistance management. The mixture might have an advantage in terms of lower cost and toxicit

Tools for delivering entomopathogenic fungi to malaria mosquitoes: effects of delivery surfaces on fungal efficacy and persistence.

BACKGROUND\ud \ud Entomopathogenic fungi infection on malaria vectors increases daily mortality rates and thus represents a control measure that could be used in integrated programmes alongside insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS). Before entomopathogenic fungi can be integrated into control programmes, an effective delivery system must be developed.\ud \ud METHODS\ud \ud The efficacy of Metarhizium anisopliae ICIPE-30 and Beauveria bassiana I93-825 (IMI 391510) (2 × 10(10) conidia m(-2)) applied on mud panels (simulating walls of traditional Tanzanian houses), black cotton cloth and polyester netting was evaluated against adult Anopheles gambiae sensu stricto. Mosquitoes were exposed to the treated surfaces 2, 14 and 28 d after conidia were applied. Survival of mosquitoes was monitored daily.\ud \ud RESULTS\ud \ud All fungal treatments caused a significantly increased mortality in the exposed mosquitoes, descending with time since fungal application. Mosquitoes exposed to M. anisopliae conidia on mud panels had a greater daily risk of dying compared to those exposed to conidia on either netting or cotton cloth (p < 0.001). Mosquitoes exposed to B. bassiana conidia on mud panels or cotton cloth had similar daily risk of death (p = 0.14), and a higher risk than those exposed to treated polyester netting (p < 0.001). Residual activity of fungi declined over time; however, conidia remained pathogenic at 28 d post application, and were able to infect and kill 73 - 82% of mosquitoes within 14 d.\ud \ud CONCLUSION\ud \ud Both fungal isolates reduced mosquito survival on immediate exposure and up to 28 d after application. Conidia were more effective when applied on mud panels and cotton cloth compared with polyester netting. Cotton cloth and mud, therefore, represent potential substrates for delivering fungi to mosquitoes in the field

Estimating above ground net biomass change in tropical and subtropical forests: refinement of IPCC default values using forest plot data

As countries advance in greenhouse gas (GHG) accounting for climate change mitigation, consistent estimates of above ground biomass (AGB) net change are needed for the tropics and subtropics. Countries with limited forest monitoring capabilities rely on 2006 IPCC default AGB net change values, which are averages per ecological zone, per continent. These previous defaults come from single studies, provide no uncertainty indications, and aggregate old secondary forests and old-growth forests. In this study, we update these default values using forest plot data. In comparison with previous estimates, new values include data published from 2006 onwards, are derived from multiple sites per global ecological zone, provide measures of variation, and divide forests >20 years old into older secondary forests and old-growth forests. We compiled 176 AGB chronosequences in secondary forests and AGB net change rates from 536 permanent plots in old-growth and managed or logged forests. In this dataset, across all continents and ecozones, AGB net change rates in younger secondary forests (go years) are higher than rates in older secondary (>20 years and ≤100 years) forests and managed or logged forests, which in turn are higher than rates in old-growth forests (> 100 years). Data availability is highest for North and South America, followed by Asia then Africa. We provide a rigorous and traceable refinement of the IPCC 2006 AGB net change default rates, identify which areas in the tropics and subtropics require more research on AGB change, and reflect on possibilities for improvement as more data becomes available

Insecticide resistance and the future of malaria control in Zambia.

BACKGROUND: In line with the Global trend to improve malaria control efforts a major campaign of insecticide treated net distribution was initiated in 1999 and indoor residual spraying with DDT or pyrethroids was reintroduced in 2000 in Zambia. In 2006, these efforts were strengthened by the President's Malaria Initiative. This manuscript reports on the monitoring and evaluation of these activities and the potential impact of emerging insecticide resistance on disease transmission. METHODS: Mosquitoes were captured daily through a series of 108 window exit traps located at 18 sentinel sites. Specimens were identified to species and analyzed for sporozoites. Adult Anopheles mosquitoes were collected resting indoors and larva collected in breeding sites were reared to F1 and F0 generations in the lab and tested for insecticide resistance following the standard WHO susceptibility assay protocol. Annual cross sectional household parasite surveys were carried out to monitor the impact of the control programme on prevalence of Plasmodium falciparum in children aged 1 to 14 years. RESULTS: A total of 619 Anopheles gambiae s.l. and 228 Anopheles funestus s.l. were captured from window exit traps throughout the period, of which 203 were An. gambiae malaria vectors and 14 An. funestus s.s.. In 2010 resistance to DDT and the pyrethroids deltamethrin, lambda-cyhalothrin and permethrin was detected in both An. gambiae s.s. and An. funestus s.s.. No sporozoites were detected in either species. Prevalence of P. falciparum in the sentinel sites remained below 10% throughout the study period. CONCLUSION: Both An. gambiae s.s. and An. funestus s.s. were controlled effectively with the ITN and IRS programme in Zambia, maintaining a reduced disease transmission and burden. However, the discovery of DDT and pyrethroid resistance in the country threatens the sustainability of the vector control programme