Process Evaluation of a Community-Based Microbial Larviciding Intervention for Malaria Control in Rural Tanzania

Microbial larviciding can be an effective component of integrated vector management malaria control schemes, although it is not commonly implemented. Moreover, quality control and evaluation of intervention activities are essential to evaluate the potential of community-based larviciding interventions. We conducted a process evaluation of a larval source management intervention in rural Tanzania where local staff were employed to apply microbial larvicide to mosquito breeding habitats with the aim of long-term reductions in malaria transmission. We developed a logic model to guide the process evaluation and then established quantitative indicators to measure intervention success. Quantitative analysis of intervention reach, exposure, and fidelity was performed to assess larvicide application, and interviews with larviciding staff were reviewed to provide context to quantitative results. Results indicate that the intervention was successful in terms of reach, as staff applied microbial larvicide at 80% of identified mosquito breeding habitats. However, the dosage of larvicide applied was sufficient to ensure larval elimination at only 26% of sites, which does not meet the standard set for intervention fidelity. We propose that insufficient training and protocol adaptation, environment and resource issues, and human error contributed to low larvicide application rates. This demonstrates how several small, context-specific details in sum can result in meaningful differences between intervention blueprint and execution. These findings may serve the design of other larval source management interventions by demonstrating the value of additional training, supervision, and measurement and evaluation of protocol adherence.

Laboratory testing of very low-copper-treated water to prolong pupation and emerging time of mosquito larvae: an alternative method to delay mosquito breeding capability

ABSTRACTIntroductionLarvicide application in ovitrap is one of the currently available methods used in mosquito eradication campaign because they eliminate the larval stage. We previously reported that copper in liquid form is a promising candidate due to its potent larvicide properties in a laboratory setting and even in the field. In the field study, several larvae survived in the ovitrap due to the dilution of copper concentration by the rain. The surviving larvae were smaller and less motile. This led our interest to study the effect of a sub-lethal dose of copper in ovitrap on larvae development, pupation time and lifespan in the adult stage.MethodsFirst instar larvae of three species of mosquito (Aedes albopictus, Culex pipiens and Anopheles stephensi) were bred in copper-treated water at a concentration of 0.60 ppm, 0.30 ppm, and 0.15 ppm and compared with the control group. The surviving larvae were recorded every day in terms of pupa emerging time and adult emerging time. The number of adult mortality was recorded and compared with the control.ResultsCopper showed potent larvicide effect in the 0.60 ppm concentration and prolonged pupation time and caused a significantly lower number of emerging mosquitoes down to the lowest concentration of 0.15 ppm. The adult lifespan was not different compared to the control.ConclusionThis study demonstrates the capability of copper below 1 ppm to prolong the pupation time and the emerging time of mosquito larvae. Our findings open the possibility of copper application to cut mosquito breeding capacity that eventually will reduce disease transmission.

Experimental studies on macroinvertebrate predator–prey impact of pesticides. The reactions of Rhyacophila and Hydropsyche (Trichoptera) larvae to Simulium larvicides

Acute toxicity tests with the predaceous trichopteran larvae of Rhyacophila dorsalis and Hydropsyche pellucidula in a laboratory-simulated stream have shown that both species have a high survival rate after short exposures, 15 min to 1 h, to concentrations of temephos(Abate) and chlorpyrifos methyl that produce a mortality of 90% or more in late-instar Simulium larvae. A similar differential reaction to the synthetic pyrethroid permethrin was demonstrated in the case of Hydropsyche but not Rhyacophila.The implication of these findings is discussed firstly in relation to the environmental impact of Simulium control programmes based on application of larvicides to rivers and streams, and secondly to the wider problem of evaluating the impact of pesticides and allied toxic chemicals on stream ecosystems.It is concluded that although significant differences in tolerance level to some insecticides between prey (Simulium) and predator (trichopteran larvae) can be demonstrated in the laboratory, the margin of safety is not sufficiently wide to assure selective control of Simulium larvae by these chemicals under the less precise conditions of larvicide application in the field.