Journal of the American Mosquito Control Association, 24(1):127–129, 2008Copyright E 2008 by The American Mosquito Control Association, Inc.
PERMETHRIN DECOMPOSITION AFTER FOUR MONTH STORAGE IN THE SPRAY TRUCK TANKS DURING MOSQUITO OFF SEASON RUI-DE XUE,1 WHITNEY A. QUALLS,1 HE ZHONG,2 AND CATE L. BROCK2 ABSTRACT. The concentrations of permethrin in the Aqua-ReslinH formulation stored in the insecticide mixers/pumps, 16 ultra-low volume (ULV) truck-mounted spray tanks, and a stock container were sampledand analyzed by gas chromatography. The result showed that an average of 55.53% and 70.32% permethrinin Aqua-Reslin were decomposed in the ULV spray truck tanks and in the mixers/pumps, respectively,during the 4-month mosquito off-season. The degradation may directly result in economic loss. Also, themosquito control efficacy may be compromised if the concentrations are inappropriate. The permethrinanalytical method, economic cost, and degradation-prevention methods are discussed in this article.
Permethrin, decomposition, adulticide, mosquito control Permethrin is a broad-spectrum pyrethroid This purpose of this study was to examine insecticide used to kill a variety of pest and whether permethrin in the truck-mounted spray vector insects. Permethrin as an active ingredient tanks and in the mixers or pumps was decom- (AI) has been formulated in a variety of pest and posed after several months or during the mos- vector control products, including several mos- quito off-season. The resulting economic cost of quito adulticides, such as Aqua-ReslinH (Bayer the degradation and its prevention were also Environmental Science, Montvale, NJ), Aqua- The assessment was conducted by taking the luerTM 20–20 (Allprovector, St. Joseph, MO).
insecticide samples from each spray tank and the Adulticides for mosquito control are usually mixers/pumps in all 4 AMCD substations. The applied at ultralow volume (ULV), by plane or sampling process includes agitating the mixture helicopter, and/or by ground, with the use of for 5 min with a handheld agitator before taking truck-mounted ULV sprayers or hand foggers.
samples from each spray tank. The water-mixed Most ground application for adult mosquito insecticide solution from the mixers/pumps was control is conducted by using ULV spray trucks.
drained to a plastic bucket and sampled from the bucket after agitation. Control samples were (AMCD) of St. John’s County, located in obtained from the insecticide stock containers northeast Florida, predominantly applies per- following the agitation after circulation. A 10-ml methrin (Aqua-Reslin), with the use of ULV sample from the middle of the spray tank and spray trucks to control adult mosquitoes from 1 ml from the stock container were taken with the use of a 10-ml disposable pipette. The samples spray trucks, and the tanks mounted on the spray were immediately placed into 50-ml centrifuge trucks are always filled to capacity with the tubes and labeled according to the truck tank permethrin product mixture during the mosquito number and date. The control sample was diluted season. The time to stop mosquito adulticide 1:10 times by using 1 part of Aqua-Reslin and application is heavily dependent on the mosquito adding 9 parts of well water. All samples weresealed, stored with coolants, and transferred to activity in a given year and could vary from the Florida Agricultural and Mechanical Univer- location to location. Therefore, all 16 tanks on sity, Public Health Entomology and Education the ULV spray trucks were loaded with Aqua- Center (FAMU/PHEREC), Panama City, FL for Reslin during the mosquito off-season from December to June. Most of the spray trucks were Within 36 h of arriving at the laboratory, all also used by the field inspectors daily and samples (Aqua-Reslin) were analyzed for per- therefore, the diluted Aqua-Reslin agitated inside methrin residue by using a gas-chromatography the tanks through the field trips daily.
(GC) method developed at FAMU/PHEREC,Panama City, FL. All samples were diluted through a series of dilution. A Varian 3400 GC Anastasia Mosquito Control District, 500 Old configured with electron capture detector (ECD) Beach Road, St. Augustine, FL 32085.
and an 8200 autosampler (Varian Analytical FAMU, Public Health Entomology Research and Education Center, 4000 Frankford Ave., Panama City, Instruments, Walnut Creek, CA) were used for the permethrin analysis. A GC CP-Sil 8 CB low- JOURNAL OF THE AMERICAN MOSQUITO CONTROL ASSOCIATION bleed capillary column (30 m 3 0.25-mm inner Aqua-Reslin formulation, after dilution with well diameter, 0.25-mm film thickness) bonded with water, was subjected to significant degradation, fused silica (Varian, Inc., Palo Alto, CA) was compared to the original stock solution. The used. Chromatograph data were acquired on control efficacy could be compromised with an a Dell Computer (Dell Computer Corporation, estimated loss of 55.3% and 70.32% permethrin One Dell Way, Round Rock, TX) equipped with (AI), respectively, if the remaining diluted prod- a data-handling software, Star Chromatography ucts are sprayed in the following year.
Workstation, Version 4.51 (Varian Analytical Many factors may contribute to permethrin Instruments). The GC injector was operated decomposition (Bouma et al. 1996, Gonzalez et isothermally at 220uC in splitless mode, and the al. 2002). The insecticide efficacy against target detector block was maintained at 300uC. The GC mosquitoes may also be influenced by other column oven temperature was held at 130uC for factors (Bouma et al. 1996), such as sprayer sample introduction, ramped at 20uC/min to calibration, rate of application, timing, tempera- 200uC and held for 1 min, ramped again at ture (Hodiati and Curtis 1999), rainfall, water 25uC/min to 280uC and held for 2 min, and then pH, sunlight, and the suitability of the chemical ramped a 3rd time at 25uC/min to 300uC and held to its purpose. The permethrin decomposition in for 3 min. The total analysis time was 13.50 min the ULV spray tanks during the mosquito off- per sample. Retention time of the permethrin season may be caused by photodegradation, hydrolysis exposure, and high or low tempera- streamlined to calculate permethrin ‘‘group’’ tures due to everyday use of the trucks.
concentrations so that reported values were The tank size of each spray truck is 15 gal and reflective of both the cis and trans isomers. An was typically filled with 1.5 gal (5.67 liters) of injection volume of 1 ml was used for all Aqua-Reslin and 13.5 gal (56.77 liters) of water.
The insecticide cost ($225 per gallon) in each tank A 5-point calibration curve (minimum 3-point), is about $337.5. During the 4-month period, the covering a permethrin concentration range from estimated loss of permethrin was about 50%. This 0.10 to 1.60 mg/ml, was generated for the analysis.
required an additional 0.75 gal (2.8 liters) of Correlation coefficients required for the calibra- Aqua-Reslin, at a cost of about $168.75 per tion curves were at least 0.995 (R2 $ 0.995). The truck. Typically, the diluted Aqua-Reslin will be analytical standard used for the calibration was stored in the spray truck tanks for 6–7 months.
Without spraying, it is assumed that all permeth- certified 96.6% pure permethrin. The analytical- rin (AI) is probably completely lost during that grade permethrin was dissolved in a small volume period of time. A spray truck with a full tank of of hexane to make a primary stock standard degraded compound is sent out for a 3–4-h spray solution with a concentration of 1 mg/ml. The mission. The estimated cost for 1 truck includes permethrin stock solution was subsequently di- the spraying labor, overtime pay, and gas cost of luted to prepare for calibration solutions. A new about $150–$200. Therefore, a total estimated permethrin calibration curve was generated for cost per truck spray will be $500–$600 during an analysis of samples for each field trial. During ineffective mission, with a grand total of $8,000– analysis, continuous calibration at a ,0.52-mg/ml $9,600 for a spraying mission with all 16 spray level was conducted every 10 samples with the use of a recovery criterion of 100 6 10%. This To minimize or prevent the possibility of continuing calibration solution was intentionally breakdown of Aqua-Reslin inside the holding prepared from a secondary source—different tank on a spray truck, we recommend continually analytical standard lot number than that used applying a spray until the tank is empty during to generate the calibration curve. Hence, this the final seasonal mission. However, this is not continuing calibration also served as a confirma- always possible. For instance, sudden weather tion standard to verify the primary analytical changes may cause a delay or interruption of the standard concentration. The secondary source of ULV spraying operation, or a sudden rise in analytical standard for the continuing calibration temperature may increase adult mosquito activity solution was also obtained from Bayer Crop late in the season, necessitating an additional Science US with certified purity of permethrin.
insecticide application. The tank mixture may be Field blanks, laboratory blanks, and instrument stored in the trucks for an unacceptable length of blanks were used to check for possible contam- time. If this occurs, a chemical residue analysis must be made to determine the lost amount of The result showed that an average of 44.47% 6 active ingredient, and the difference must be 12.68% (n 5 16) and 29.68% 6 14.13% (n 5 6) made up by adding more Aqua-Reslin stock.
original Aqua-Reslin remained inside the spray In addition, the remaining water-mixed in- tank mounted on the truck and in the insecticide secticide solution siphoned out from the spray mixers/pumps, respectively, after 4 months dur- tanks or mixers/pumps after the season in 2006 ing the mosquito off-season. This suggested that was analyzed. The test result showed that the permethrin concentration in siphoned insecticide a research report only and the AMCD neither solution stored in a sealed container for 4– endorses nor opposes the commercial products 5 months was similar to the concentration in the spray truck tank stored for 4–5 months.
In conclusion, compared with freshly mixed samples, water-diluted permethrin in Aqua-Re- slin product decomposed inside the holding tanks Bouma MJ, Parvez SD, Nesbit R, Sondorp HE. 1996.
mounted on spray trucks after being stored in the Rapid decomposition of permethrin in the outer fly tanks for several months. This loss of permethrin of an experimental tent in Pakistan. J Am Mosq does not only affect control efficacy, but also causes the economic loss. The decomposition Gonzalez Audino P, Licastro SA, Zerba E. 2002.
Thermal decomposition and isomerization of cis- could be detected by residue analysis that will permethrin and beta-cypermethrin in the solid phase.
help the determine the make-up concentration, and could be prevented by spraying until the tank Hodiati MH, Curtis CE. 1999. Effects of permethrin at is empty and other practice measures. Analyses of different temperatures on pyrethroid-resistant and the synergist, pipernyl butoxide (PBO) and inert susceptible strains of Anpoheles. Med Vet Ent material in the product were not made. This is


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