Influence of Portland cement amendment on soil pH and residual soil termiticide performance

Pest Management Science Pest Manag Sci 62:1216–1223 (2006)

Influence of Portland cementamendment on soil pH and residual soiltermiticide performanceDina L Richman,1 Cynthia L Tucker2 and Philip G Koehler2∗1FMC Corporation, 1735 Market Street, Philadelphia, PA 19103, USA2Department of Entomology and Nematology, University of Florida, Gainesville, FL 32611, USA

Abstract: Soil adjacent to new brick veneer work is likely to have a higher pH owing to the mixture of cementwith the soil. In the Gainesville, FL, area, soil samples taken from such locations had a range of pH values from9.0 to 10.1; similar soils used in bioassays had a pH of 5.6 before the addition of cement. Addition of 15 mg ofPortland cement to 33 g of soil increased the pH to 6, and addition of 291 mg of Portland cement increased thepH to 9. The pH of soil amended with cement was stable for the first 5 months. After 10 months, soil pH valuesdecreased from alkaline to near neutral in all cases. Eastern subterranean termite workers, Reticulitermes flavipes(Kollar), were exposed to the treated soil at pH 6–9 for 24 h, and percentage mortality was recorded at 5 days,5 months and 10 months. Termite mortality significantly decreased at higher soil pHs for bifenthrin, chlorpyrifos,fipronil and imidacloprid treatments at 5 months and similarly for bifenthrin, permethrin, chlorpyrifos, fiproniland imidacloprid treatments at 10 months. There was an inverse linear relationship between soil pH and mortality.Increased soil pH diminished residual activity of termiticide in the following order: imidacloprid > fipronil >

chlorpyrifos = bifenthrin > permethrin > cypermethrin. 2006 Society of Chemical Industry

Keywords: EST; cypermethrin; termiticide degradation; soil treatment

1 INTRODUCTIONEffective soil termiticide treatments are expected toprotect a structure and its contents from subter-ranean termites for at least 5 years1 even thoughresidues decline over time.2 In concrete slab tests inFlorida, chlorpyrifos (Dursban; Dow AgroSciences,Indianapolis, IN; 1% applied to soil) failed in one often plots after 9 years,1 cypermethrin (Prevail FT;FMC Corp., Philadelphia, PA; 0.5% applied to soil)failed in one of ten plots after 5 years and permethrin(Dragnet FT; FMC Corp.; 0.5% applied to soil)failed in two of ten plots after 4 years.1,3 The goal ofinitial treatment is to apply sufficient termiticide to thesoil to compensate for termiticide degradation overtime.

Key factors that affect the rate of termiticidedegradation include chemical, photochemical andmicrobial factors, leaching, run-off, volatilization,bioaccumulation in plants and animals4 and sizeof area treated.5 Soil degradation rates have beendetermined for chlorpyrifos, bifenthrin, permethrinand cypermethrin when applied at termiticidalconcentrations. Soil type significantly affects therate of termiticide degradation.2 In laboratory andfield trials, half-lives of termiticides in different soilsranged from 23 to 462 days for chlorpyrifos (analyticalgrade,6 Dursban; Dow AgroSciences; 1000 mg kg−1

in soil7–10), from 5 to 1410 days for bifenthrin

(analytical grade; FMC Corp.; 100 mg kg−1 in soil;8

and Biflex FT; FMC Corp.; 31 mg kg−1 in soil9),from 22 to 45 days for permethrin (Dragnet FT;FMC Corp.; 50 mg kg−1 in soil9) and approximately12 days for cypermethrin (Prevail FT; FMC Corp.;30 mg kg−1 in soil9). In general, registered termiticidesare persistent in the most common soil types andshould protect structures for at least 5 years.

Treatment failures within 5 years of constructionare common, however, in spite of the persistenceof soil termiticides. For example, 15% of houses2–6 years old in St Johns County, Florida, thatreceived a soil termiticide treatment at the time ofconstruction were infested by termites as reportedby homeowners.11 Many factors can cause treatmentfailures, including termite abundance and behavior,inadequate termiticide application and lack of treat-ment uniformity.2,12–14 However, the influence ofcertain construction products on the termiticide bar-rier is virtually unknown.

Cement and mortar are found at virtually everyhome construction site. Portland cement is the mostcommon masonry cement used in brick veneer mortarand cement foundations.15 It consists of calciumand/or magnesium carbonate, and, when mixed withsoil, it can increase soil pH as it hydrolyzes to calciumand/or magnesium hydroxide. The purpose of the

∗ Correspondence to: Philip G Koehler, University of Florida, Department of Entomology and Nematology, Natural Area Drive, PO Box 110620, Gainesville,FL 32611, USAE-mail: [email protected](Received 27 July 2005; revised version received 4 March 2006; accepted 7 April 2006)Published online 18 September 2006; DOI: 10.1002/ps.1274

2006 Society of Chemical Industry. Pest Manag Sci 1526–498X/2006/$30.00

Influence of soil pH on termiticide activity

present study was to determine the effect of Portlandcement on soil pH and on degradation of variousconcentrations of termiticides as indicated by mortalityof eastern subterranean termites, Reticulitermes flavipes(Kollar), in a 24 h bioassay.

2 MATERIAL AND METHODS2.1 Soil pH analysisSoil pH of samples taken adjacent to homes wasdetermined by the protocol of the University of FloridaInstitute of Food and Agricultural Sciences SoilTesting Laboratory. This method requires that 33 gof soil (25 mL) and 50 mL of distilled water be stirredtogether in a paper cup. One subsample of each soilmixture was used. To determine the soil pH, mixtureswere left to stand for 30 min, and then stirred again.The pH was then determined with a pH-meter (FisherNo. 13-620-290: pencil thin gel filled combinationelectrode with BNC; Hanna, Pittsburgh, PA).

2.2 Field pH soil samplingSoil was collected from within 10 cm of the foundationof 27 homes in Gainesville, Florida (a horizon soil:loamy, siliceous, thermic Arenic Paleudults),16 for thepurpose of determining the pH range for laboratorybioassays. Nine newly completed structures (<2 weeksold), nine five-year-old structures, and nine ten-year-old structures were sampled. The exteriors of thenine structures in each age group comprised threestucco, three wooden siding and three brick veneer.Soil at 10 cm from structural walls was collected usinga metal pipe (10.16 cm ID) inserted 20 cm into thesoil. Individual soil samples were shaken loose fromthe pipe into labeled plastic bags. The experiment wasa 3 × 3 factorial design (3 claddings by 3 ages).

2.3 Soil amendment with cementSoil consisting of fine loamy sand (a horizon soil:loamy, siliceous, thermic Arenic Paleudults)16 wascollected near the University of Florida UrbanEntomology Laboratory, Gainesville, Florida, ovendried (177 ◦C for 24 h) and sieved (Fisher No. 16;Hanna, Pittsburgh, PA). Soil pH was determinedfor three subsamples of untreated soil. Initial pHdetermination was for three soil samples (33 g).A weighed amount of Portland masonry cement(Quikcrete, type ‘S’; Quikcrete International Inc.,Atlanta, GA) was then added to each sample, stirredand left to stand for 30 min before pH redetermination.This process was repeated until the quantities ofcement needed to raise the soil pH to approximately6, 7, 8 and 9 were determined. Based on thesecement quantities, 33 g soil samples were amendedwith cement to achieve soil pH values of 6, 7, 8 and9. Three samples were prepared at each pH. Soil waswetted with distilled water to 10% moisture. Waterwas added every 7–10 days to maintain the original wetweights. Soil was loosely covered with aluminum foiland kept in the dark at ambient room temperature and

humidity. Soil pH was determined at 1 day, 5 monthsand 10 months after addition of cement.

2.4 InsectsEastern subterranean termites were field collectedfrom three widely separated colonies in Gainesville,FL. Traps consisted of PVC tubes (54 cm long,10 cm diameter) placed vertically in the ground toa depth of ≈12 cm and covered with a PVC cap(10 cm diameter; NIBCO, Elkhart, IN).17 Two rollsof single-faced corrugated cardboard [236 × 20 cm(rolled to ≤10 cm diameter); Hesco, Waverly, FL]were stacked into the tube as a food source. Termiteswere extracted from the cardboard and stored atroom temperature (≈23 ◦C) in plastic sweater boxeswith moist corrugated cardboard for ≤1 week beforeinclusion in the bioassay.

2.5 TermiticidesSix termiticides were used in this study: bifen-thrin 79 g L−1 SC (Talstar termiticide/insecticide;FMC Corp., Philadelphia, PA), chlorpyrifos 440 g L−1

EC (Dursban; Dow AgroSciences, Indianapolis,IN), cypermethrin 253 g L−1 EC (Demon; Syn-genta Corp., Greensboro, NC), fipronil 91 g L−1 SC(Termidor SC; Aventis/BASF, Montvale, NJ), imi-dacloprid 214 g L−1 SC (Premise 2; Bayer Envi-ronmental Science, St Louis, MO) and permethrin256 g L−1 EC (Prelude; Syngenta Corp., Greens-boro, NC). Distilled water was used to make all insec-ticide dilutions and served as the control treatment(0 mg kg−1 insecticide). Stock dilutions of each ter-miticide (2.1 mL of Premise 2, 20.9 mL of Dursban

TC, 5.6 mL of Termidor SC, 7.5 mL of Talstar T,42.0 mL of Prelude or 21.0 mL of Demon TC in100 mL of water) were prepared in 100 mL volumetricflasks. Three 1:9 serial dilutions were then made fromeach stock dilution.

2.6 Soil termiticide treatmentsThe 33 g soil samples were amended with cement toachieve pH values of 6, 7, 8 and 9. Soil was thenplaced in plastic weighing boats (13 × 13 cm). Thesoil in the weight boat was treated with 3.3 mL of thestock dispersion of termiticide or a serial dilution ofthis and stirred to uniformly moisten the mixture(10% moisture).18 The concentration ranges usedwere 10 000, 1000, 100, 10 and 0 mg AI kg−1 soilfor chlorpyrifos and permethrin; 5000, 500, 50, 5and 0 mg kg−1 for cypermethrin; 600, 60, 6, 0.6 and0 mg kg−1 for fipronil and bifenthrin; and 500, 50, 5,0.5 and 0 mg kg−1 for imidacloprid. In each case thehighest concentration was 10 times the highest labelrate of application. The treated soils were air driedin a hood for at least 5 days to allow solvents in theformulation to evaporate. Controls were prepared withthe same procedure, but using distilled water.

2.7 Termiticide bioassaysBioassays were conducted over a 10 month testingperiod. Original weights were determined for all

Pest Manag Sci 62:1216–1223 (2006) 1217DOI: 10.1002/ps

DL Richman, CL Tucker, PG Koehler

soil termiticide treatments and controls (soil +cement + liquid + weigh boat). To allow hydrolysis oftermiticide, distilled water was added every 7–10 daysto maintain the original weight throughout the10 month testing period. Weighing boats were stackedin plastic tubs (one tub for each termiticide) withsteel mesh screen between layers. Tubs were looselycovered with aluminum foil and kept in the dark atambient room temperature and humidity.

Groups of ten worker termites each (undifferen-tiated larvae of at least the third instar) were eachplaced on 7 g subsamples of treated soil contained incovered 29.57 mL plastic cups and held in the dark.Dead termites were counted after 24 h termiticideplacement in plastic cups. Bioassays were conducted5 days, 5 months and 10 months after soil treatment.

The experiment consisted of 396 experimental unitsconsisting of ten termites and treated soil/cementmixture in a plastic cup. Six termiticides wereevaluated in a 5 (concentrations) by 4 (pH) by 3(time intervals) factorial design replicated 3 times fora total of 360 experimental units. Three replicateswere derived from three termite colonies. Untreatedcontrols were prepared for each pH and time interval,replicated 3 times, and consisted of 36 experimentalunits. After evaluation of termite mortality and termiteremoval, soil on control units was used to assaypH. Termites were not added to the controls. Inaddition, soil treated with imidacloprid at 0, 5 and50 mg kg−1 was bioassayed separately and termiteswere held in covered cups for 7 days so that the fulleffect of imidacloprid could be determined. Soil inexperimental units was finely sprayed with distilledwater every 24 h to prevent desiccation. The additionalassay was replicated, and dead termites were countedat 7 days. This assay was a 3 (concentrations) by 4(pH) factorial design, replicated 3 times.

2.8 Data analysisThe pH data for soil collected from near buildingswere analyzed using a two-way analysis of variance(ANOVA) to determine effects of cladding type andbuilding age (α = 0.05) on pH.19 The amount ofcement needed to adjust laboratory soil pH to 6, 7, 8and 9 at 5 days was determined by linear regression,and pH measurements of these adjusted soils over timewere analyzed by one-way ANOVA to determine effectof aging (0, 5 and 10 months) for each pH. Means wereseparated using Scheffe’s test (α = 0.05).19

Termite mortality data were arcsine square roottransformed and analyzed by one-way ANOVAto determine the effect of soil pH for eachtermiticide concentration at 0, 5 and 10 months aftertreatment. Means were separated using Scheffe’stest (α = 0.05).19 The relationship between timeperiod and pH on mean percentage termite mortalitywas estimated by linear regression for the highesttermiticide concentrations at which pH significantlyaffected mortality. Significant differences for slopeswere determined by non-overlap of 95% confidenceintervals.19

3 RESULTS AND DISCUSSION3.1 Field pH soil samplingFine loamy sand soils in Gainesville, FL, typicallyrange from pH 4.5 to 6.5.16 However, soil samplestaken near buildings had a wide range of measuredpH values, from 5.20 to 10.10 (Table 1). Exteriorcladding, structural age and their interaction did notsignificantly affect soil pH. Lack of significance may bedue to two main factors. First, the foundations of allbuildings were composed of concrete and/or mortar.Resulting Portland cement contamination caused anelevated soil pH for most samples regardless of age.Second, contamination of soil with cement probablywas not uniform around buildings and resulted in highsample variability. As a result, significant differencesin pH probably did not occur because most soilsamples were more alkaline than normal with highvariability caused by cement contamination probablynot occurring uniformly.

Although alkaline soils are not usually found inthe Gainesville area, high pH values may occur insoil adjacent to new brick veneer work if the soilbecomes contaminated with Portland cement duringthe construction process. Increased pHs may lead toinactivation of pyrethroid termiticides by hydrolysis.20

3.2 Effect of cement on soil pH in the laboratoryPortland cement added to the soil increased the pH(Fig. 1). Soil pH amended with cement was stable forthe first 5 months, then after 10 months alkaline soilpH values significantly decreased to near neutral.

This change in the laboratory soil pH may haveoccurred owing to a combination of microbial actionand cation exchange capacity of the soil. Although soil

Table 1. pH of soil collected within 10 cm of structures (n = 27) located in Gainesville, FLa

Mean soil pH (±SEM) [min. to max.]

Structure age Stucco Wooden siding Brick veneer

<2 weeks 6.47 (±0.45) [5.60–7.10] 6.77 (±0.64) [5.50–7.60] 8.90 (±0.72) [7.60–10.10]5 years 7.80 (±0.26) [7.30–8.20] 7.83 (±0.35) [7.20–8.40] 8.57 (±0.26) [8.10–9.00]10 years 7.80 (±0.26) [5.20–8.40] 7.43 (±0.69) [6.60–8.80] 7.27 (±0.46) [6.50–8.10]

a ANOVA resulted in no significant interaction between cladding and age, and no significant differences in mean soil pH between houses of differentcladdings or ages. Two-way ANOVA – cladding: DF = 2, MS = 2.9633, F = 2.82, P = 0.0863; age: DF = 2, MS = 1.5478, F = 1.47, P = 0.2562;cladding × age: DF = 4, MS = 1.4544, F = 1.38, P = 0.2797.

1218 Pest Manag Sci 62:1216–1223 (2006)DOI: 10.1002/ps


y = -4E-05x2 + 0.0222x + 5.7886R2 = 0.9769

5

6

7

8

9

10

0 100 200 300 400Cement (mg)

pH

Figure 1. Relationship between amounts of cement added to 33 g ofsoil and resulting pH.

was baked before use, it was not sterilized or kept ina sterile environment. Therefore, microbes could haveaided in shifting the soil back towards acidic pH.21 Thegreatest change in soil pH over the 10 month periodwas in soil that started at 9.07. This change wasprobably due to the cation exchange capacity of soil,which increases with soil pH.21 Also, water was addedto soil every 7–10 days so that evaporation occurred.This wet–dry regime could have contributed to theslow change in pH over time.

3.3 Termiticide bioassaysInitially, an increase in pH lowered termite mortality.The increase in pH probably increased termiticidedegradation (Table 2).

Table 2. Percentage mortality (±SE) of termites held on soil treated with six termiticidesa

TermiticideConcentration

(mg kg−1) n pH 5 daysb 5 monthsb 10 monthsb 10 months 7 daysc

Cypermethrind 5 3 6 100.00 100.00 100.00 –3 7 100.00 100.00 93.33 (±6.67) –3 8 100.00 100.00 100.00 –3 9 100.00 100.00 97.67 (±2.33) –

Bifenthrine 0.6 3 6 100.00 63.33 (±1.93) a 73.90 (±7.73) a –3 7 100.00 48.90 (±1.10) ab 40.00 (±10.00) ab –3 8 100.00 20.10 (±7.59) bc 18.90 (±6.75) bc –3 9 100.00 10.00 (±5.77) c 2.23 (±2.33) c –

Permethrinf 10 3 6 100.00 100.00 51.27 (±1.27) a –3 7 100.00 100.00 31.23 (±2.70) ab –3 8 100.00 100.00 17.80 (±2.20) bc –3 9 100.00 100.00 5.57 (±2.94) c –

Chlorpyrifosg 10 3 6 100.00 100.00 a 100.00 a –3 7 100.00 89.90 (±11.10) ab 100.00 –3 8 100.00 74.47 (±4.00) ab 53.23 (±2.23) b –3 9 100.00 54.43 (±15.55) b 29.10 (±0.90) c –

Fipronilh 6 3 6 100.00 86.67 (±1.93) a 97.77 (±2.23) a –3 7 100.00 90.57 (±0.57) a 57.77 (±23.23) b –3 8 100.00 92.20 (±1.10) a 44.60 (±6.01) bc –3 9 100.00 18.90 (±7.27) b 21.10 (±2.20) c –

0.6 3 6 62.20 (±0.00) a 66.67 (±0.00) a 83.33 (±3.84) a –3 7 53.33 (±2.67) a 66.67 (±0.00) a 61.13 (±5.57) ab –3 8 63.43 (±2.02) a 65.47 (±1.23) a 52.53 (±3.07) bc –3 9 62.00 (±4.00) a 1.00 (±1.00) b 22.43 (±8.06) c –

Imidaclopridi 50 3 6 100.00 71.10 (±10.93) a 10.00 (±0.00) a 100.003 7 100.00 54.43 (±4.43) ab 11.01 (±1.10) a 100.003 8 100.00 39.97 (±3.33) b 7.77 (±4.00) ab 100.003 9 100.00 32.20 (±1.10) b 0.00 b 100.00

5 3 6 44.43 (±1.13) a 28.87 (±7.27) a 0.00 43.33 (±3.33) a3 7 47.77 (±2.23) a 12.23 (±2.93) ab 0.00 28.90 (±1.00) ab3 8 44.43 (±1.13) a 8.90 (±2.20) b 0.00 25.57 (±2.94) b3 9 46.67 (±1.93) a 00.00 c 0.00 24.43 (±4.43) b

a Percentage mortality was arcsine square root transformed before analysis. Means within a column treatment group followed by the same letter arenot significantly different at α = 0.05.b Mortality was recorded 24 h after introduction.c Mortality was recorded 7 days after introduction.d 5000, 500 and 50 mg kg−1 cypermethrin caused 100% mortality; untreated controls had 0% mortality.e 600, 60 and 6 mg kg−1 bifenthrin caused 100% mortality; untreated controls had 0% mortality.f 10 000, 1000 and 100 mg kg−1 permethrin caused 100% mortality; untreated controls had 0% mortality.g 10 000, 1000 and 100 mg kg−1 chlorpyrifos caused 100% mortality; untreated controls had 0% mortality.h 600 and 60 mg kg−1 fipronil caused 100% mortality; untreated controls had 0% mortality.i 500 mg kg−1 imidacloprid caused 100% mortality; 0.5 mg kg−1 and untreated controls had 0% mortality.



3.3.1 CypermethrinAs soil aged for 10 months, pH reduced theresidual activity of 5 mg kg−1 cypermethrin-treatedsoil (Table 2), the lowest concentration that killedall termites in the 5 day bioassay. Su et al.9 alsofound that cypermethrin (formulated as Prevail) at3000 mg kg−1 in soil of unknown pH degraded throughtime with an estimated half-loss time of 11.9 monthsin Florida soils and 2.8–10.7 months in Texas soils.Kard22 reported that 1.0% AI cypermethrin spraysolutions applied to soil were stable for 8 to >12 yearsand provided 100% protection in US Forest Serviceconcrete slab tests. However, in the present study,increased soil pH reduced mortality of termitesconfined on soil treated with 5 mg kg−1 cypermethrinand aged for only 5–10 months.

3.3.2 BifenthrinAs soil aged for 5–10 months, pH significantly reducedthe residual activity of 0.6 mg kg−1 bifenthrin-treatedsoil (Table 2), the lowest concentration that killed alltermites in the 5 day bioassay. Similarly, Smith andRust23 reported that 3 h exposure of R. hesperus Bankson 1 mg kg−1 bifenthrin-treated soil resulted in 100%mortality at 24 h. Kard22 reported that 0.062% AIbifenthrin spray solutions applied to soil were stablefor 7 to >13 years and provided 100% protection inUS Forest Service concrete slab tests. However, Suet al.9 found that bifenthrin (formulated as Biflex) at310 mg kg−1 in soil of unknown pH degraded throughtime with an estimated half-loss time of 5.3 months inFlorida soils and 4.3–8.7 months in Texas soils. Thefluoride in the bifenthrin should theoretically make itstable in alkaline soil,20 but residual activity may alsobe affected by inert ingredients.20,24 The present studyindicates that 0.6 mg kg−1 bifenthrin degraded fasterin high-pH soil, resulting in lower termite mortalityfor pH 9 soil than for pH 6 soil at only 5–10 monthsafter soil treatment.

3.3.3 PermethrinIn soil aged for 10 months, pH significantly reducedthe residual activity of 10 mg kg−1 permethrin-treatedsoil (Table 2), the lowest concentration that killedall termites in the 5 day bioassay. Similar resultswere reported by Smith and Rust23 who found100% mortality of R. hesperus confined on 10 mg kg−1

permethrin-treated soil for 3 h. However, Su et al.9

found that permethrin (formulated as Dragnet FT) at5000 mg kg−1 in soil of unknown pH degraded throughtime with an estimated half-loss time of 21.9 monthsin Florida soils and 6.5–15.2 months in Texas soils. Inthe present study, mortality was 100% for all pH levelsat the 5 month bioassay. Increased soil pH significantlyreduced the mortality of termites confined to soiltreated with permethrin at 10 mg kg−1 and aged for10 months.

3.3.4 ChlorpyrifosAs soil aged for 5–10 months, pH significantly reducedthe residual activity of 10 mg kg−1 chlorpyrifos-treated soil (Table 2), the lowest concentration thatkilled all termites in the 5 day bioassay. Smithand Rust23 reported rapid mortality of termitesfor ≥10 mg kg−1 chlorpyrifos-treated soil, killing alltreatment-confined termites within 24 h. They alsoreported that 50 mg kg−1 chlorpyrifos killed 100% ofR. hesperus within 7 h. Kard22 reported that 0.5% AIchlorpyrifos spray solutions applied to soil were stablefor 3–7 years and provided 100% protection in USForest Service concrete slab tests.

The present authors found that >7.0 soil pHsignificantly decreased the mortality of treatment-confined termites in 10 mg kg−1 chlorpyrifos-treatedsoil at 10 months; mortality of termites in 100 mg kg−1

treated soil was not affected. Similarly, Racke et al.25

reported chlorpyrifos could have a half-life of only3 months at 10 mg kg−1 in alkaline Florida andTexas soils, while a concentration of 1000 mg kg−1

retarded hydrolysis. Also, Murray et al.10 foundthat the stability of chlorpyrifos at 1000 mg kg−1 isunaffected by natural soil alkalinity. These higherconcentrations of chlorpyrifos probably degradedmore slowly than lower concentrations because achlorpyrifos metabolite, 3,5,6-trichloro-2-pyridinol, isantimicrobial and retards microbial degradation.26

Chlorpyrifos was degraded by hydrolysis underalkaline conditions,24 but chlorpyrifos hydrolysisat higher concentrations would be limited by its∼0.73 mg L−1 water solubility.9 The dose-dependentdegradation of chlorpyrifos in alkaline soils that wasseen in the present study can therefore be explainedby the influence of microbial degradation and limitedwater solubility.

3.3.5 FipronilAs soil aged for 5–10 months, pH significantly reducedthe residual activity of 6 mg kg−1 fipronil-treated soil(Table 2). Fipronil has been shown to be a non-repellent, slow-acting contact insecticide.19,27 In thepresent study, it differed from the organophosphateand pyrethroid treatments in that it caused less than100% mortality of termites in the initial bioassay.Osbrink et al.27 reported approximately tenfold higherLT90 for R. virginicus (Banks) compared with lethaltimes for termites exposed to chlorpyrifos, permethrinor cypermethrin. Also, fipronil in sand, soil and clay at5 mg kg−1 required 5–10 days to cause 100% mortalityof Coptotermes formosanus Shiraki in test tube tunnelingassays.28 Therefore, the 24 h exposure used in thepresent study probably was not enough time forfull expression of termite mortality from exposure tofipronil.

3.3.6 ImidaclopridAs soil aged for 5 and 10 months, pH significantlyaffected the residual activity of 5 and 50 mg kg−1

imidacloprid-treated soils (Table 2). Imidacloprid is a



non-repellent, slow-acting contact termiticide.18,29–32

In the present study, soil treated with imidaclopridat 50 mg kg−1 caused less than 100% mortality oftermites in the initial bioassay. Boucias et al.29 foundthat at least 3 days exposure to soil treated with50–100 mg kg−1 technical imidacloprid was needed

before termites began dying. Therefore, the 24 hexposure used in the present study probably was notenough time for full expression of termite mortalityfrom imidacloprid. All termites exposed for 7 daysto 50 mg kg−1 imidacloprid in soil aged for 10 monthsdied at all pH levels. However, 5 mg kg−1 imidacloprid

0

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6 7 8 9

pH

% M

orta

lity

Chlorpyrifos 10 mg kg-1 (1/100)Imidacloprid 50 mg kg-1 (label)Fipronil 6 mg kg-1 (1/10)Bifenthrin 6 mg kg-1 (1/100)Permethrin 10 mg kg-1,Cypermethrin 5 mg kg-1 (1/100)

#

#

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^

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+ ++

+

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Y=100

Y=192.80 - 15.11(pH)r2 = 0.59, C.I. {-19.48, -10.75}

Y=225.57 - 20.42(pH)r2 = 0.52, C.I. {-26.32, -14.52}

Y=147.80 - 13.12(pH)r2 = 0.73, C.I. {-16.90, -9.33}

Y=177.18 - 18.88(pH)r2 = 0.88, C.I. {-24.33, -13.43}

Figure 2. Mortalities (24 h) of Reticulitermes flavipes confined on soil of pH 6, 7, 8 or 9, treated with termiticides and aged for 5 months. Confidenceintervals (95%) for slopes in curly brackets.

0

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6 7 8 9pH

% M

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Chlorpyrifos 10 mg kg-1 (1/100)

Imidacloprid 50 mg kg-1 (label)

Fipronil 6 mg kg-1 (1/10)

Bifenthrin 6 mg kg-1 (1/100)

Permethrin 10 mg kg-1 (1/100)

Cypermethrin 5 mg kg-1 (1/100)

# #

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l

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Y=98.00 - 0.03(pH)r2 = 0.01, C.I. {-0.04, -0.02}

Y=266.08 - 26.11(pH)r2 = 0.89, C.I. {-33.64, -18.57}

Y=237.72 - 24.32(pH)r2 = 0.93, C.I. {-31.35, -17.30}

Y= 21.67 - 23.71(pH)r2 = 0.85, C.I. {-30.55, -16.87}

Y= 138.87 - 15.00(pH)r2 = 0.95, C.I. {-19.33, -10.67}

Y=32.22 - 3.33(pH)r2 = 0.51, C.I. {-4.30, -2.37}

Figure 3. Mortalities (24 h) of Reticulitermes flavipes confined on soil of pH levels 6, 7, 8 or 9, treated with termiticides and aged for 10 months.Confidence intervals (95%) for slopes in curly brackets.



killed 30.6% of the termites after 7 days. Imidaclopriddegraded faster at high pH, resulting in low termitemortalities.

4 SUMMARYLinear regression analysis of termite mortality after24 h exposure to treated soil aged for 5 monthsindicated an inverse relationship between pHand termite mortality for bifenthrin, chlorpyrifos,fipronil and imidacloprid treatments (Fig. 2). Con-fidence intervals of slopes for these four treat-ments overlapped at 5 months (Fig. 2). There wasan inverse relationship between pH and termitemortality at 10 months for bifenthrin, permethrin,chlorpyrifos, fipronil and imidacloprid treatments(Fig. 3). At 5 mg kg−1, cypermethrin killed all ter-mites within 24 h. Soil pH had the greatest effecton residual activity of termiticides at the concen-trations presented in Figs 2 and 3, in the follow-ing order: imidacloprid > fipronil > chlorpyrifos =bifenthrin > permethrin > cypermethrin.

The present results agree with those reported byother researchers, and all are justification for consid-ering soil pH when making termiticide applications toconstruction sites. Alkaline pH values caused degra-dation of chlorpyrifos,8,25 imidacloprid,33,34 fipronil35

and pyrethroids36 in solution. Portland cementincreased the pH of soil around structures and underlaboratory conditions. According to the present lab-oratory study, addition of Portland cement to soiltreated with low concentrations of chlorpyrifos, imi-dacloprid, fipronil, bifenthrin or permethrin degradedthe termiticides, as indicated by reduced termite mor-tality. Contamination with cement and degradationof termiticide by elevated pH within the termiticidetreatment area around new construction could easilybe reduced by use of a drop cloth to catch excesscement.

ACKNOWLEDGEMENTSThe authors thank Gil Marshal for his help with the soiltreatments and with the pH readings. This researchwas partly funded by Dow AgroSciences. They wouldespecially like to thank Ellen Thoms for her supportwith funding and guidance related to this project. Theywould also like to thank Joseph Smith for reviewingthis manuscript.

REFERENCES1 Kard BM, Mauldin JK and Jones SC, Evaluation of soil

termiticides for control of subterranean termites (Isoptera).Sociobiology 15:285–297 (1989).

2 Gold RE, Howell HN, Pawson BM, Wright MS and Lutz JC,Persistence and bioavailability of termiticides to subterraneantermites (Isoptera: Rhinotermitidae) from five soil types andlocations in Texas. Sociobiology 28:337–363 (1996).

3 Wagner T, Mulrooney J, Shelton T and Peterson C, Reducedrisk products stealing spotlight. Pest Control February: 16–23(2003).

4 Rao PSC, Bellin CA, Brusseau ML and Linn DL, Couplingbiodegradation of organic chemicals to sorption and transportin soils and aquifers: paradigms and paradoxes, in ’91 Sorptionand Degradation of Pesticides and Organic Chemicals in SoilConference, Denver, CO. Soil Science Society of America,Madison, WI, pp. 1–26 (1993).

5 Su NY, Ban PM, Chew V and Scheffrahn RH, Size and edgeeffects of concrete plots on chlorpyrifos degradation in sub-slab sand. J Econ Entomol 92:409–415 (1999).

6 Racke KD, Coats JR and Titus KR, Degradation of chlorpyrifosand its hydrolysis product, 3,5,6-trichloro-2-pyridinol, in soil.J Environ Sci Health B 23:527–539 (1988).

7 Di HJ, Aylmore LAG and Kookana RS, Degradation ratesof eight pesticides in surface and subsurface soils underlaboratory and field conditions. Soil Sci 163:404–411 (1998).

8 Baskaran S, Kookana RS and Naidu R, Degradation of bifen-thrin, chlorpyrifos, and imidacloprid in soil and beddingmaterials applied at termiticidal application rates. Pestic Sci55:1222–1228 (1999).

9 Su NY, Ban PM and Scheffrahn RH, Longevity and efficacyof pyrethroid and organophosphate termiticides in fielddegradation studies using miniature slabs. J Econ Entomol92:890–898 (1999).

10 Murray RT, von Stein C, Kennedy IR and Sanchez-Bayo F,Stability of chlorpyrifos for termiticidal control in sixAustralian soils. J Agric Food Chem 49:2844–2847 (2001).

11 Richman DL, Influence of construction characteristics andhome maintenance practices on subterranean termite infesta-tion rates in northeastern Florida. PhD Dissertation, Universityof Florida, Gainesville, FL (2003).

12 Macalady DL and Wolfe NL, New perspectives on thehydrolytic degradation of the organophosphorothioate insec-ticide chlorpyrifos. J Agric Food Chem 31:1139–1147 (1983).

13 Felsot AS, Enhanced biodegradation of insecticides insoil: implications for agroecosystems. Ann Rev Entomol34:453–476 (1989).

14 Forschler BT and Townsend ML, Mortality of eastern subter-ranean termites (Isoptera: Rhinotermitidae) exposed to foursoils treated with termiticides. J Econ Entomol 89:678–681(1996).

15 Allen E, Fundamentals of Building Construction Materials andMethods. John Wiley & Sons, Inc., New York (1999).

16 Thomas BL, Cummings E and Wittstruck WH, Soil surveyof Alachua County, Florida. United States Department ofAgriculture, Soil Conservation Service, Washington, DC(1985).

17 Powell TE, Eastern subterranean termite (Isoptera: Rhinotermi-tidae) tunneling in soil treated with nonrepellent termiticides.Master’s Thesis, University of Florida, Gainesville, FL (2000).

18 Gahlhoff JE, Penetration and survivorship of the easternsubterranean termite, Reticulitermes flavipes (Kollar), intovarious thicknesses of termiticide-treated soil. Master’s Thesis,University of Florida, Gainesville, FL (1999).

19 SAS Version 8e for Windows. SAS Institute, Cary, NC (2000).20 Naumann K, Synthetic Pyrethroid Insecticides: Structures and

Properties. Springer-Verlag, Berlin, Germany (1990).21 Brady NC and Weil RR, The Nature and Properties of Soils.

Prentice-Hall, Upper Saddle River, NJ (1999).22 Kard BM, Gulfport termite control testing results. Florida Pest

Association Annual Termite Symposium, USDA Forest Service(2000).

23 Smith JL and Rust MK, Tunneling response and mortality ofthe western subterranean termite (Isoptera: Rhinotermitidae)to soil treated with termiticides. J Econ Entomol 83:1395–1401(1990).

24 Harris CR, Factors influencing the effectiveness of soilinsecticides. Ann Rev Entomol 17:177–198 (1972).

25 Racke KD, Fontaine DD, Yoder RN and Miller JR, Chlorpyri-fos degradation in soil at termiticidal application rates. PesticSci 42:43–51 (1994).

26 Somasundaram L, Coats JR, Racke KD and Stahr HM, Appli-cation of the Microtox system to assess the toxicity of



pesticides and their hydrolysis metabolites. Bull Environ Con-tam Toxicol 44:254–259 (1990).

27 Osbrink WA, Lax AR and Brenner RJ, Insecticide suscepti-bility in Coptotermes formosanus and Reticulitermes virginicus(Isoptera: Rhinotermitidae). J Econ Entomol 94:1217–1228(2001).

28 Osbrink WA and Lax AR, Effect of tolerance to insecticideson substrate penetration by Formosan subterranean termites(Isoptera: Rhinotermitidae). J Econ Entomol 95:989–1000(2002).

29 Boucias DG, Stokes C, Storey G and Pendland JC, The effectsof imidacloprid on the termite Reticulitermes flavipes andits interaction with the mycopathogen Beauveria bassiana.Pflanzenschutz-Nachrichten Bayer 49:103–145 (1996).

30 Kuriachen I and Gold RE, Evaluation of the ability of Retic-ulitermes flavipes (Kollar), a subterranean termite (Isoptera:Rhinotermitidae), to differentiate between termiticide treatedand untreated soil in laboratory tests. Sociobiology 32:151–168(1998).

31 Ramakrishnan R, Suiter DR, Nakatsu CH and Bennett GW,Feeding inhibition and mortality after exposure toimidacloprid-treated soils. J Econ Entomol 93:422–428(2000).

32 Gahlhoff JE and Koehler PG, Penetration of the easternsubterranean termite into soil treated at various thicknessesand concentrations of Dursban TC and Premise 75. J EconEntomol 94:486–491 (2001).

33 Sarkar MA, Biswas PK, Roy S, Kole RK and Chowdhury A,Effect of pH and type of formulation on the persistenceof imidacloprid in water. Bull Environ Contam Toxicol63:604–609 (1999).

34 Zheng W and Liu W, Kinetics and mechanism of the hydrolysisof imidacloprid. Pestic Sci 55:482–485 (1999).

35 Bobe A, Cooper JF, Coste CM and Muller MA, Behavior offipronil in soil under Sahelian Plain field conditions. Pestic Sci52:275–281 (1998).

36 Camilleri P, Alkaline hydrolysis of some pyrethroid insecticides.J Agric Food Chem 32:1122–1124 (1984).


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Influence of Portland cement amendment on soil pH and residual soil termiticide performance