Evaluation of Pyriproxyfen Effects on Aedes aegypti and Predatory Mosquito Toxorhynchites rutilus (Diptera: Culicidae)

Control of mosquito vectors of pathogens remains heavily dependent on the application of conventional insecticides. Pyriproxyfen (PPF) is a novel insecticide that has been proposed for use in autodissemination techniques to control mosquito vectors. The use of PPF can inhibit adult emergence but does not inhibit larval development. This feature is favorable for controlling Aedes aegypti because PPF has the potential to work in combination with natural sources of mortality (competition, predation) during the immature stages, and other control methods, including biocontrol agents that further suppress recruitment of adult mosquitoes. However, the PPF effects on life-history traits of Ae. aegypti in comparison to predatory mosquito Toxorhynchites rutilus, a source of mortality, are not fully understood. Here, we show that larval exposure to PPF concentrations that inhibit 50–90% of adult emergence in Ae. aegypti had a negligible effect on adult emergence and lifespan of Tx. rutilus. Weights of adult Ae. aegypti and Tx. rutilus were not influenced by PPF. These findings suggest that the use of PPF to control mosquito vectors may have low effects on mosquito biocontrol agents. Our results extend and confirm earlier data showing that PPF has potential to implement with Tx. rutilus to suppress Ae. aegypti and provide an additional advantage of PPF use in autodissemination control strategies.

Potential Distribution of the Biocontrol Agent Toxorhynchites rutilus By 2070

ABSTRACT Climate change projections indicate that mosquito distributions will expand to include new areas of North America, increasing human exposure to mosquito-borne disease. Controlling these vectors is imperative, as mosquito-borne disease incidence will rise in response to expansion of mosquito range and increased seasonality. One means of mosquito control used in the USA is the biocontrol agent, Toxorhynchites rutilus. Climate change will open new habitats for its use by vector control organizations, but the extent of this change in habitat is currently unknown. We used a maximum entropy approach to create species distribution models for Tx. rutilus under 4 climate change scenarios by 2070. Mean temperature of warmest quarter (22.6°C to 29.1°C), annual precipitation (1,025.15 mm to 1,529.40 mm), and precipitation seasonality (≤17.86) are the most important bioclimatic variables for suitable habitat. The center of current possible habitat distribution of Tx. rutilus is in central Tennessee. Depending upon the scenario, we expect centroids to shift north-northeast by 97.68 km to 280.16 km by 2070. The extreme change in area of greater than 50% suitable habitat probability is 141.14% with 99.44% area retained. Our models indicate limited change in current habitat as well as creation of new habitat. These results are promising for North American mosquito control programs for the continued and potential combat of vector mosquitoes using Tx. rutilus.

Interaction of Mycobacterium ulcerans with Mosquito Species: Implications for Transmission and Trophic Relationships

ABSTRACT Mycobacterium ulcerans is the causative agent of Buruli ulcer, a severe necrotizing skin disease that causes significant morbidity in Africa and Australia. Person-to-person transmission of Buruli ulcer is rare. Throughout Africa and Australia infection is associated with residence near slow-moving or stagnant water bodies. Although M. ulcerans DNA has been detected in over 30 taxa of invertebrates, fish, water filtrate, and plant materials and one environmental isolate cultured from a water strider (Gerridae), the invertebrate taxa identified are not adapted to feed on humans, and the mode of transmission for Buruli ulcer remains an enigma. Recent epidemiological reports from Australia describing the presence of M. ulcerans DNA in adult mosquitoes have led to the hypothesis that mosquitoes play an important role in the transmission of M. ulcerans. In this study we have investigated the potential of mosquitoes to serve as biological or mechanical vectors or as environmental reservoirs for M. ulcerans. Here we show that Aedes aegypti, A. albopictus, Ochlerotatus triseriatus, and Culex restuans larvae readily ingest wild-type M. ulcerans, isogenic toxin-negative mutants, and Mycobacterium marinum isolates and remain infected throughout larval development. However, the infections are not carried over into the pupae or adult mosquitoes, suggesting an unlikely role for mosquitoes as biological vectors. By following M. ulcerans through a food chain consisting of primary (mosquito larvae), secondary (predatory mosquito larva from Toxorhynchites rutilus septentrionalis), and tertiary (Belostoma species) consumers, we have shown that M. ulcerans can be productively maintained in an aquatic food web.