Black flies (Diptera: Simuliidae) are common pests of humans and wild and domesticated birds and mammals around the world. These insects develop as larvae and pupae in flowing water. The adult black fly emerges into the terrestrial environment and is day-active. The most effective and efficient technique to suppress adult populations is to target the larvae while they are concentrated in rivers and streams. The larvae are highly susceptible to the insecticidal proteins produced by Bacillus thuringiensis subsp. israelensis (Bti), which lyse the cells of the gut. An Integrated Pest Management approach to black fly suppression includes identifying the pest species and then conducting larval surveillance to locate the nearest larval habitats. Each species has an optimal larval habitat, with some preferring large, warm rivers and others preferring smaller, shaded streams. Accurate identifications are essential to focus larvicide applications to the proper habitats where the pests are developing. Bti-based larvicides are applied to the targeted waterways based on the flow characteristics and the general hydrological parameters. The number of application sites will be determined by the expected “carry” of the Bti proteins downstream and the resulting mortality produced. The carry is correlated with the volume and rate of flow of the treated waterway. Larger, faster flowing waterways have more energy in the current to keep the larvicide particles suspended in the water column where the feeding black fly larvae can filter them from the flow. Larval mortality can be evaluated in-stream or by collecting samples post-exposure and evaluating mortality after 24-hours. Larvicide applications are based on the ecology of the pest species and access to the targeted larval habitats. Applications can be conducted by hand, helicopter, or boat, depending on the size of the waterway and the resources available.

Black fly suppression with the biological larvicide, Bacillus thuringiensis subsp. israelensis

ACS Fall 2021

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