INCREASED WATER HARDNESS IN CATCH BASINS TREATED WITH SPINOSAD (NATULAR XRT) EXTENDED RELEASE TABLETS

In response to apparent lack of efficacy of spinosad treatments of storm drain catch basins in Marathon, Florida, we investigated water quality parameters where drains had been treated with Natular® XRT extended release tablets. An analysis of water samples from these sites revealed that alkalinity and water hardness differed significantly between treated and untreated drains. However, when tested in a semi-field environment protected from runoff, differences in alkalinity were not associated with spinosad treatment, whereas water hardness increased over time in replicates treated with Natular XRT. Water quality may be a reason for poor larval control rather than product failure or resistance. Future work will investigate whether changes in water hardness associated with spinosad treatment may impact the efficacy of this larvicide at reducing adult emergence in field environments.