Laboratory and field studies were conducted with Bacillus thuringiensis var. israelensis (BTI) to determine its effect upon Aedes taeniorhynchus and non-target organisms in the salt marsh. Toxicity tests indicated that salt-marsh mud reduced the activity of BTI. With corrections, BTI killed over 99% of the mosquito larvae in the field at concentrations of 4.5 IU/ml and above. Out of 39 species collected prior to treatment, only Notonecta indica showed a significant decrease in population. However, this genus is known to fly from deteriorating habitats.