Influence of Stream Profile and Abiotic Factors on the Performance and Residual Dosages of Two Commercial Formulations of Bacillus thuringiensis subsp. israelensis During a 2-Year Experiment

Recently, results of a 3-year study showed the importance of abiotic factors such as water temperature, stream discharge and the hyporheic zone on the behaviour, performance and loss of the residual dosages (amount of the injected dosage left at each station) of two commercial liquid formulations of Bacillus thuringiensis subsp. israelensis ( Bti ), Teknar HP-D and Vectobac 1200L. Experiments were performed in the same stream and under environmental conditions that allowed comparisons of results between formulations. To improve our understanding of the influence of abiotic factors on the behaviour and the performance of these formulations, a 2-year experiment using the same products was conducted in another river characterized by a much different profile, higher discharges and colder temperatures. A field procedure based on a system of gutters located on the bank of the river already used in the previous 3-year experiment was utilized. Black fly larval mortalities were recorded along the river at different distances (stations) to evaluate the behaviour and the performance of the products while water samples taken at the stations were tested in the laboratory against mosquito neonate larvae to evaluate the residual dosages of Bti at each station. Results showed that higher residual dosages of the Vectobac 1200L were recovered compared to Teknar HP-D along the river. Although higher dosages were recovered, higher mortality was observed only for the Vectobac 1200 L in high discharge conditions. As seen before, the hyporheic zone (interstitial water between the streambed and groundwater) produced a major loss of the dosages in the first meters of the river. But because of the river profile, the hyporheic zone had a lesser effect on the loss of the dosages further in the river resulting in very long carries for both Teknar HP-D and Vectobac 1200L.

Keywords:

• Carry
• Residual
• Dosages
• Formulations
• Black
• Hyporheic
• Zone
• Bioassays
• Discharge
• Water
• Temperature
• Stream
• Profile