ABSTRACT

Biodac is a cellulosic-based granule manufactured from recyclable paper waste and has been used as a carrier for granular formulations. A field evaluation was performed on Aedes sollicitans using a two month old formulation of methoprene on Biodac. At 5 lbs. per acre (1.5 oz. A.L.L. per acre), 50% adult emergence inhibition was realized. Methoprene on Biodac presents no problems in terms of formulation or application and appears economically attractive relative to other granular larvicides.

INTRODUCTION

Methoprene has been tested and used as an effective larvicide for many years to control both freshwater and saltmarsh mosquitoes. In heavily vegetated or forested wetlands larval control by any larvicide is often best achieved by use of a granular pesticide formulation to allow penetration of the canopy. Temephos and Bti granules are commercially available and liquid methoprene (Altosid Liquid Larvicide - A. L. L.) can be formulated on site with sand, however, some agencies have limited or discontinued the use of "Altosand" because of the heavy payload and abrasiveness of sand on dispersal equipment (McNelly and Lesser, 1994).

Biodac is an inert cellulose-based granule manufactured from recyclable paper waste from the paper industry. It comes in a variety of mesh sizes and is manufactured by Granulation Technology, Inc., a division of Edward Lowe Industries. Biodac has been widely used in the agriculture and lawn care industries as a carrier for formulations including pesticides. It was a combination of utilizing a recycled paper carrier, the product's uniform size, and its non-abrasive, free-flowing, dust-free characteristics that led the mosquito control section to consider this as a carrier for larvicides. In this field trial, we evaluated methoprene formulated on Biodac.

MATERIALS AND METHODS

For this evaluation, two batches (125 lbs. each) of a 0.10% methoprene/Biodac formulation were made on 14 June, 1994 by the authors according to Sandoz Agro, Inc. specifications. Under this formulation, the recommended application rate of 10- 1 3 lbs. per acre would be the equivalent of 3 oz. A.L.L. per acre. For each batch 2.5 lbs. (32.5 oz.) each of A.L.L. and water were mixed in a pressurized hand sprayer. There was some concern as to whether or not the methoprene would be mixed evenly on the Biodac due to the absorbency of Biodac (vs. adsorption on sand). To address this issue, 0.5 oz. of Rhodamine dye was added to the tank mix so the granules could be visually checked for spray coverage. Three 40-pound bags of Biodac (12/20 mesh) were loaded into a 5 cu. ft. mortar mixer and the methoprene mix was sprayed, using a fine spray nozzle setting, onto the Biodac while it was mixing. The granular formulation was allowed to continue mixing for approximately five minutes after the spray was applied. The granules were then loaded back into the Biodac bags, appropriately labeled and sealed.

The field evaluation was conducted on Bombay Hook National Wildlife Refuge in Kent County, Delaware on 10 August, 1994 at 1645 hours under 5-10 mph wind conditions. A 15-acre test plot containing isolated mosquito-breeding depressions (potholes) was treated. The plot was located in irregularly flooded saltmarsh dominated by salt hay (Spartina patens/Distichlis spicata) and some saltmarsh cordgrass (Spartina alterniflora). There was little or no surface pellicle at the time of application. The product was aerially applied at a rate of 5 lbs. per acre using a Rockwell Thrush Commander airplane outfitted with a Transland granular spreader. The plane had been calibrated earlier in the summer using blank material. Also, at the time of the test, collection pans were laid out across the spray swath to calculate the actual field application rate. The product was applied to a third instar brood of Aedes sollicitans.

Thirty-six hours following the treatment the site was revisited. Ten mosquito-breeding potholes were selected for post-treatment monitoring. Twenty pupae or fourth instar larvae from each pothole were placed in rearing containers with approximately 500 ml. of habitat water and taken back to the lab. Cone-shaped emergence traps were then placed in the potholes to monitor adult emergence in the field. Approximately 50 pupae and larvae were also collected from a composite of ten potholes in an untreated control site for lab rearing and emergence traps were placed in the potholes for field monitoring.

RESLULTS

The results of the field test are presented in Table 1. On 14 August a 48-hour post-treatment inspection revealed as much as 58 % reduction in larval densities on both the treated and control sites. For this reason a composite control sample was collected. On 15 August the sites were again revisited. At the treatment site there were no adult mosquitoes on wing in any of the emergence traps. Many of the traps had dead pupae and dead emerging adults on the surface. The traps at the control site had many adults on wing and emerging -adults and pupal cases on the surface. All traps still contained some late instar larvae.

In the lab, similar larval mortality was noted. Sixty-four percent of the larvae in the control died with the remaining larvae emerging successfully. In the treatment containers pupal mortality or adult emergence inhibition ranged from 50 to 100 percent with an average of 82 percent. The rearing containers were checked daily until 29 August when all pupae had either died or emerged successfully.

DISCUSSION

The Biodac granules evaluated (mesh size 12/20) were free-flowing and presented no problems in terms of mixing and application. A small amount of wet granules clung to the mixing paddles but these were easily broken apart by hand. The granules are highly absorbent but the methoprene mix covered evenly and thoroughly as indicated by the dye that was added. It was essentially dust-free which is an advantage over celetom or sand.

There was a definite indication of methoprene-induced mortality. Because of the relatively high control mortality, standardizing for natural mortality using Abbott's (1925) constant resulted in an average of 50% adult emergence inhibition. Improved laboratory rearing conditions or collecting only pupae for lab rearing could provide more quantitative results. The fact that the product was applied at only half the recommended rate (5 lbs. or 1.5 oz. A.L.L. per acre) could indicate that this is perhaps the lower end of the range for acceptable operational utility. Also, the product was in formulation for two months prior to testing which could indicate a limited shelf life. Future field tests could help define these parameters.

From an economical standpoint, A.L.L. on Biodac seems highly competitive. If purchased by the truckload the cost of the Biodac and shipping is $0.19 per lb. (C.Kleczko, GranTech Products; pers. comm.). Assuming it takes two pesticide applicators one hour to mix 500 lbs. of Biodac and methoprene, an average formulation cost of $0.06 per lb. was calculated. With an application cost of $3.50 per acre, the total product and application cost at 5 lbs. per acre was $6.84 per acre. This was less expensive than Vectobac CG, Abate 2G or Abate 5G.

CONCLUSION

In this field evaluation a 0. 1 0 % methoprene formulation on Biodac granules applied at 5 lbs. per acre provided an average of 82% mosquito emergence inhibition. However, due to high control mortality, the adjusted percent emergence inhibition was 50%. Because of its physical qualities, Biodac shows good potential as a larvicidal carrier and can be a useful tool in mosquito control where a granular formulation is recommended. Methoprene on Biodac presents no problems in its formulation or application. Methoprene formulated on Biodac appears to be effective and economically attractive.

ACKNOWLEDGMENTS

The authors wish to thank Allen Chorman, Inc. for assisting in the calibration and the aerial application of the tested product.

REFERENCES CITED

Abbott, W.S., 1925. A method of computing the effectiveness of an insecticide. J. Econ. Ento. 18:265-267.

McNelly J. R. and C. R. Lesser, 1994. Laboratory and field evaluation of methoprene formulated on Biodac. Proc. N.J. Mosq. Control Assoc. 18:17-21.

Table 1. Results of a 0. 10 % methoprene formulation on Biodac granules applied at 5 lbs. per acre* to Aedes sollicitans in Delaware.