ABSTRACT: Bacillus sphaericus is a naturally occurring bacteria that has been isolated, cultured, and labeled as VectoLex® for mosquito control. The purpose of this study was to test the effects of VectoLex® on the target organism Aedes larvae and non-target organisms (copepods, amphipods, and rotifers) in the laboratory and in the field. Unfortunately, poor conditions prevented experimentation in the field so only work in the laboratory was done. B. sphaericus killed 99+% of Aedes larvae 24 hours post-treatment at dilutions greater than 0.1 ppm. At concentrations at or below 0.01 ppm, larval control was not adequate. B. sphaericus did not seem to have much of an impact on the non-target organisms. The treated copepods and amphipods in fact, seemed to survive as well (if not better) than the controls at doses ranging up to 1000 ppm. The treated rotifers showed good survival throughout the experimental period at doses ranging up to 1000 ppm. The laboratory studies give us a baseline for the responses of target and non-target organisms to B. sphaericus. However, these responses do not necessarily guarantee the same results in the field. The goal for 1999 is to continue tests in the laboratory as well as to proceed with experimentation of Bs. sphaericus in the field on Aedes larvae and non-target organisms.

Bacillus sphaericus is a naturally occurring bacteria - isolated, cultured, and labeled for mosquito control. The bacteria is supplied by Abbott Laboratories as VectoLex® and comes impregnated on corn cob granules. Bacillus sphaericus acts as an endotoxin to mosquito larvae. It is consumed by the larvae as live bacteria. The bacteria is able to penetrate through the intestines of the mosquito larvae into the hemocoel. Once in the hemocoel, B. sphaericus reproduces and releases lethal doses of toxin killing the mosquito larvae.

Ruber, et al. (1997) obtained excellent control of Aedes cantator larvae with VectoLex® at doses of 10 and 20 lbs./acre, but could not test for extended time periods. After 48 hours at doses of 10 and 20 lbs./acre, 99+% of Aedes larvae were dead. During the same period, the control plots maintained high numbers of Aedes larvae. Poor weather conditions prevented experimentation after the first brood.

Ruber, et al. (1997) also found evidence of VectoLex® effect on non-target harpacticoid Copepoda at doses of 10 and 20 lbs./acre. The study showed that the number of harpacticoids were reduced significantly in the field four days post-treatment (at 10 and 20 lbs./acre). However, since the number of harpacticoids in the treated plots 48 hours post-treatment was statistically greater than the number of harpacticoids in the control plot, the meaning of the data was unclear.

The purpose of this research was to examine the residual effectiveness of Bacillus sphaericus, as VectoLex®, on Aedes larvae in the field beyond one brood. Also, to continue the study of the potential effects of B. sphaericus on non-target organisms in the laboratory and to determine the effective lethal dosage of VectoLex® on Aedes larvae for comparison with non-target organisms.

Since the summer of 1998, we have been testing the effects of VectoLex® on Aedes larvae and non-target organisms (copepods, amphipods, and rotifers) strictly in the laboratory. The study of VectoLex® effects on Aedes larvae in the field is the major objective for 1999.

Aedes larvae were obtained from Ipswich, MA; Copepoda and Rotifera from Rowley, MA; and Amphipoda from Nahant, MA.

Applications in the lab - Aqueous dilutions of VectoLex® were made: 1000, 100, 10, 1, 0.1, 0.01, 0.001, and 0 ppm (control). Each dilution was run in triplicate against Aedes larvae and the non-target organisms (copepods, amphipods, and rotifers). Dishes were censused for mortality at 24, 48, 72, 96, 120, and 144 hours post-treatment.

We are presenting only results of Aedes larvae, copepods, and amphipods at 48 hours post-treatment (figure 1). These results are fairly representative of the whole experimental time span.

The Aedes larvae showed very good survival in the control plates at 48 hours post-treatment. However, at concentrations of VectoLex® equal to or greater than 0.1 ppm, ranging up to 1000 ppm, the Aedes larvae showed 99+% mortality after 48 hours post-treatment. In fact, these same results were found after 24 hours. At concentrations equal to or less than to 0.01 ppm after 48 hours, inadequate Aedes larvae control was achieved -only about 50% were killed.

Copepods showed excellent survival 48 hours after treatment at all VectoLex® concentrations tested, including the control plates (0 ppm). The amphipods also showed excellent survival 48 hours after treatment at all VectoLex® concentrations tested, including the control plates.

From 24 hours on, VectoLex® at or greater than 0.1 ppm killed =1> 99% of Aedes larvae. None of the doses (up to 1000 ppm) resulted in mortalities of copepods and amphipods. Substantial survival of rotifers was also seen at all concentrations. As far as our work goes then, we would expect no harmful effects on copepods, amphipods, and rotifers from field application of VectoLex®.

Ernest Ruber, Jack A. Card, Daniel L. Graf, Maggie Bowers, Robin Januszewski, and Walter G. Montgomery. 1997. Experiments on the Control of Salt Marsh Aedes cantator and Ae. sollicitans with Bacillus sphaericus (VectoLex®) and an Assessment of Possible Side-effects to Copepods. Proc. Northeastern Mosquito Control Association.