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Crop Protection 25 (2006) 542–548

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Residual and sublethal effects of fenpyroximate and pyridaben on theinstantaneous rate of increase of Tetranychus urticae

Minsik Kim, Cheolho Sim, Dongyoung Shin, Eunho Suh, Kijong Cho�

Division of Environmental Science and Ecological Engineering, Korea University, Anam-dong, Sungbuk-ku, Seoul 136-701, Republic of Korea

Received 5 March 2004; received in revised form 5 January 2005; accepted 24 August 2005

Abstract

The residual and sublethal effects on Tetranychus urticae Koch adult mortality, and their influence on the reproduction and population

growth, were evaluated after exposure to fenpyroximate and pyridaben. The effects on the reproduction were divided into two parts and

analyzed separately to determine the contribution to the population growth parameter, the instantaneous rate of increase (ri); (1)

reproduction on survivors (RS, number of eggs produced), and (2) survivors of progeny (SP, number of immatures developed). The RS

and SP were censused 3 and 6 days after treatment, respectively. The direct toxic effects on female adults on treatment with

fenpyroximate were always higher and more persistent than those with pyridaben, whereas the effects on the RS and SP were always

higher with pyridaben. When the ri was the evaluated endpoint, the RS ri and SP ri for both acaricides declined as the concentration

increased, but the reduction was always greater with exposure to pyridaben. The residual effects on the RS ri and SP ri remained strong

over the range of residual days tested for both acaricides. The negative values of the SP ri with all the pyridaben treatments indicated that

the pyridaben possessed strong and persistent ovicidal activity against T. urticae. The effective concentration (EC50) that reduced the

RS ri or SP ri by 50% was always higher than 50% of the lethal fenpyroximate concentration (LC50), but the opposite was true with

pyridaben, suggesting that pyridaben treatment would be more devastating to the T. urticae populations than fenpyroximate. The results

of this study indicate that fenpyroximate and pyridaben have different direct acute toxicity and reproduction effects in T. urticae, even

though they share the same mode of action: mitochondrial electron transport inhibition.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Two spotted spider mite; Residual effects; Reproduction; Population growth; Reproductive bioassay; METI-acaricides

1. Introduction

Acaricides play a major role in the management of thetwo-spotted spider mite, Tetranychus urticae Koch, popu-lations that cause significant yield losses in many field andgreenhouse crops worldwide (Parrella and Jones, 1987).Numerous chemical acaricides have been intensively usedto control T. urticae, and this species has developedresistance to widely different classes of acaricides. Thedegree of resistance to many established acaricides hasresulted in a demand for new resistant-free acaricides withnovel modes of action (Devine et al., 2001). One suchgroup of compounds is the METI (mitochondrial electrontransport inhibitors)-acaricides, of which fenpyroximate

e front matter r 2005 Elsevier Ltd. All rights reserved.

opro.2005.08.010

ing author. Tel.: +822 3290 3064; fax: +82 2 925 1970.

ess: kjcho@korea.ac.kr (K. Cho).

and pyridaben have been developed (Hirata et al., 1995)and commercially released in Korea (Kim, 2002). Goodefficacy against all developmental stages of the spider mitewas reported (Dekeysers et al., 1994), but resistance toMETI-acaricides has already been reported from Korea(Cho et al., 1995; Kim, 2002).One of the most important factors governing the

management of acaricide use is the availability of soundbaseline data on the susceptibility of target mite species tothe acaricides. Mortality is the predominant laboratoryendpoint of interest for measuring the effectiveness ofacaricides against T. urticae, and is frequently expressed asthe median lethal concentration (LC50) (Cho et al., 1995;Devine et al., 2001; Nauen et al., 2001; Stumpf and Nauen,2001) which is specific to particular life-history stages. Itcan only detect changes in the susceptibility expressed at astage under specific environmental conditions (Kammenga

ARTICLE IN PRESSM. Kim et al. / Crop Protection 25 (2006) 542–548 543

and Laskowski, 2000). Highly standardized bioassaymethods, where the response of only one developmentalstage is tested, give precise estimates of the response, butthe very nature of such precision may destroy the predictivevalue of the results as they pertain to target populations(Robertson and Worner, 1990).

The residual effects together with the sublethal effects ofacaricides on T. urticae are a crucial consideration whenmaking a pesticide selection (Kerns and Stewart, 2000). Itis important when examining the possible effects toconsider the pesticide actions that cause direct mortality,as well as those manifested through the residual andsublethal effects, for estimating a meaningful measure ofthe pesticide’s impact on a target species (Stark et al.,1997). Along with the direct mortality, the reproduction ofsurvivors and survivors of progeny after chronic exposureto acaricides should be considered to obtain a realisticprediction or extrapolation of the efficacy of an acaricide.

Robertson and Worner (1990) recommended that thepopulation response, rather than the response of indivi-duals selected for their uniform characteristics, must beemphasized in laboratory bioassays to predict the re-sponses that are likely to occur in a field population. Oneapproach for evaluating the total effect of pesticide atpopulation levels is the use of demographic parameters asendpoints of the pesticide effects. Population growth, andin particular the intrinsic rate of increase (rm) orinstantaneous rate of increase (ri), has been recommendedas a superior laboratory bioassay endpoint to that of theLC50 because it combines the lethal and sublethal effectsinto one meaningful measure (Stark et al., 1997; Kammen-ga and Laskowski, 2000).

Most studies with fenpyroximate and pyridaben havefocused on the aspects of the direct mortality to the treatedT. urticae (Devine et al., 2001; Nauen et al., 2001; Stumpfand Nauen, 2001). Clearly, studies that elucidate thepopulation growth versus individual mortality followingexposure to fenpyroximate and pyridaben are needed, so thata realistic prediction of the effects of the acaricides can beobtained. To fully achieve the control efficacy with a reducedamount of the acaricides, information on the sublethal effectsin association with the residual effects is needed.

In this study, the sublethal and residual effects offenpyroximate and pyridaben on T. urticae were measuredto predict their overall effects at the population level moreaccurately. Two acaricide effect endpoints were compared:the first involved determining the population growth withan instantaneous rate of increase (ri) for the measure ofinterest; the second was the EC50, defined as the exposureconcentration that reduces the ri by 50%.

2. Materials and methods

2.1. Mite cultures and test chemicals

The acaricides tested were fenpyroximate (5 SC; DongbuHannong Chemicals, Seoul, Korea) and pyridaben (20 SC;

Hankook Samgong Chemicals, Seoul, Korea), which werechosen because they have such vastly different effects onthe hatching in T. urticae eggs (Kim, 2002).Young adult female T. urticae (o8 days old) were used

from stock cultures of fenpyroximate-resistant (FR) andpyridaben-resistant (PR) strains, which exhibited signifi-cantly different susceptibilities to fenpyroximate andpyridaben, and have been referred to previously as thestandard resistant strains (Sim, 2000). Each strain wasmaintained separately in the laboratory at 2672 1C,60710% RH, with a photoperiod of 16:8 (L:D) h onkidney bean (Phaseolus vulgaris (L.)) seedlings. Bothstrains were continuously pressured with treatments with20.7 ppm of active ingredient (AI) fenpyroximate and8059.0 ppm of AI pyridaben for the FR and PR strains,respectively.

2.2. Reproductive bioassays and population growth studies

The kidney bean plants were grown in individual smallplastic pots (10 cm in diameter) in a greenhouse to the two-leaf stage. Sublethal concentrations of the two chemicalswere chosen from the 72-h acute concentration–responsecurves generated from the responses of adult females (Sim,2000). The probit equations for the FR and PR strainsagainst fenpyroximate and pyridaben, respectively, are asfollows: fenpyroximate; y ¼ 1.41 log(x)+2.66, pyridaben;y ¼ 1.25 log(x)�0.388, where x and y are the concentrationand probit scale, respectively. Probit scale 5 is equivalent tothe LC50. The sublethal concentrations consisted of LC0

(untreated), LC10 (fenpyroximate: 6.4 ppm; pyridaben:2101.3 ppm), LC30 (fenpyroximate: 20.7 ppm; pyridaben:8059.0 ppm) and LC50 (fenpyroximate: 46.6 ppm; pyrida-ben: 20446.5 ppm).The acaricides were applied to both sides of the leaves

until run-off, with a two-liter hand-held sprayer. Plantssprayed with tap water served as controls. After treatment,the plants were kept in a greenhouse and one leaf per plantwas taken at 1-, 3-, 5-, 7- and 9-days after treatment.Therefore, five different residual periods were establishedfor each sublethal concentration. This was done to simulatethe different ages of residues on the plants in thegreenhouses.Individual 5.3 cm-diameter leaf disks were prepared by

trimming the leaves taken from the treated plants atvarious residue ages. The disks were placed on cotton padswith the lower leaf surface facing up in Petri dishes (10 cmin diameter) filled with distilled water. Ten adult femalemites (o8 days old) from each strain were placed on eachdisk and stored at 2771 1C, 60710% RH, with aphotoperiod of 16:8 (L:D) h. The mite populations werepurposely started at the adult stage to allow rapidpopulation growth within a short-time frame (6 days).The populations on the disks were counted daily for 6

days, after exposure to 1-, 3-, 5-, 7- and 9-day old acaricideresidues by recording each number of eggs, immature andadult T. urticae populations. Therefore, the cumulative

ARTICLE IN PRESSM. Kim et al. / Crop Protection 25 (2006) 542–548544

numbers of T. urticae were counted at each observationdate. The 6-day time interval was chosen to provide enoughtime for the T. urticae to reproduce eggs and immatures todevelop, but not enough time for the mites to develop tothe adult stage. Therefore, all adults found on the diskswere from the initial and not the subsequent populations.Adults were considered dead if they could not move onebody length after being prodded with a Camel’s hair brush.Each treatment was replicated three times (30 individualfemales) and the controls were replicated six times (60females).

A measure of the population growth called an instanta-neous rate of increase (ri) was used as a bioassay endpoint,which was calculated by the following equation (Walthalland Stark, 1997):

ri ¼lnðN f=N0Þ

t, (1)

where Nf is the final number of animals, N0 the initialnumber of animals, and t the change in time (the number ofdays the experimental run). A positive ri value indicates agrowing population, and ri ¼ 0 a stable population and anegative ri value a population in decline and headingtoward extinction. The ri was calculated from the numberof individuals in a starting and ending population, withoutdetailed schedules of survivorship and fecundity.

To determine if residual days and sublethal concentra-tions of fenpyroximate and pyridaben affected the repro-duction of survivors (RS) and survivors of progeny (SP)differently at the organization of populations, two ri valueswere estimated and compared between the differentsublethal concentrations and residual ages. First, the ri

was calculated using the total numbers of eggs counted 3days after treatment, and the second included only thenumbers of immatures at 6 days after treatment. Therefore,each ri accounted for the RS and SP ri’s, respectively. After3 days, the numbers of eggs declined due to either fewereggs being laid or their development to immatures. A 6-daytime interval was chosen for the RS as most eggs developedto the immatures during this time period coupled with thedeterioration of the testing arena (leaf disk).

The median effective concentration (EC50) that reducedthe instantaneous rate of increase (ri) by 50% wasestimated by fitting the data to the following model(Haanstra et al., 1985):

y ¼c

ð1þ expðbðx� aÞÞÞ, (2)

where y is ri, x the natural logarithm of the testconcentrations, a the logarithm of the EC50, b the slopeparameter and c the ri in the control. The parameters a andb were estimated using the PROC NLIN procedure in theSAS procedures (SAS Institute, 1996). Substitutions weremade for the EC50s into the probit equations estimated bySim (2000) to determine the corresponding predicted probitmortalities at those concentrations.

2.3. Statistical analysis

All data were tested for normality with the Shapiro–WilkW statistic (Shapiro and Wilk, 1965). Data that were notnormally distributed (Po0:05) were transformed prior toanalysis of variance (ANOVA; SAS Institute, 1996).Proportional adult survivorship was transformed usingan arcsine-square-root function prior to ANOVA. Propor-tional hazards regression analysis (PHREG, SAS proce-dure PHREG, Allison 1995; SAS Institute, 1996) wasused to test for differences between the survivorship curvesof adult T. urticae for each acaricide. For each residualday, the PHREG was used to compare subsets of thesurvivorship curves equivalent to all possible pairwisesublethal treatment combinations. When significant differ-ences in the offspring production among the sublethalconcentrations were found by ANOVA, the mean valueswere separated using Tukey’s studentized range honestsignificant difference (HSD) test. A two-way analysisof variance (ANOVA) (residue age� sublethal concentra-tion) was performed on the ri estimates (SAS Institute,1996).

3. Results

3.1. Direct toxic effects on T. urticae adults

Effects of the residual and sublethal activities offenpyroximate and pyridaben on the mortalities ofT. urticae adults, expressed as a proportion of thesurvivors, are shown in Fig. 1. According to results ofthe PHREG analysis, the survivorship curves for theuntreated controls were not significantly different over arange of various residual days (P40:25) or betweenacaricides (P40:13), suggesting that the survivorships ofthe T. urticae adults were not affected by the bean leaf agewithin the residual days tested in this study.Survivorships of the adult mites declined as the

concentrations of both acaricides increased, but thesurvival curves between the LC10 and LC30 sublethalconcentrations did not differ (P40:05) over the entirerange of residual days (Fig. 1). The persistency of theresidual effects was evaluated by comparing the survivor-ship curves from the untreated control plants. With thefenpyroximate treatment, the survivorship curves gener-ated from all the sublethal concentrations were significantlydifferent from the controls up to the residual day 5. Afterthis, the slopes of the curves increased rapidly as the stagesof the residual ages increased, but showed no differencesfrom the controls (P40:05). With the pyridaben treatment,the intensities and persistency of the residual effects werevery weak compared to those of fenpyroximate. Afterresidual day 3, there were no differences in the sublethaleffects from those in the controls. These results indicatedthe direct toxic effect on the adult mites was more severeand persistent with fenpyroximate than with pyridaben.

ARTICLE IN PRESS

Pyridaben9 DAT

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Pyridaben5 DAT

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2101.3 ppm (LC10) 8059.0 ppm (LC30)20446.5 ppm (LC50)Control

Fenpyroximate9 DAT

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6.4 ppm (LC10)20.7 ppm (LC30)46.6 ppm (LC50)Control

Fig. 1. Survivorship curves of adult Tetranychus urticae at various residue days for fenpyroximate and pyridaben treated with 3 different sublethal

concentrations. The mortalities at each sublethal concentration and residue age were counted at 1-day intervals for 6 days. The thick line in each graphic

panel indicates changes in the control mortality for each residue day.

M. Kim et al. / Crop Protection 25 (2006) 542–548 545

3.2. Effects on reproduction

The mean numbers of offspring produced in the twountreated controls were virtually identical, indicating thatthe biological performance of the two T. urticae strains wasthe same in the acaricide-free environment (Table 1). Theegg production decreased in a concentration-dependentmanner with both acaricides, but a higher reduction wasobserved when the T. urticae was exposed to pyridaben.At the same concentration, the T. urticae exposed topyridaben produced approximately two-fold fewer eggsthan those exposed to pyridaben. The residual effects onthe egg production were not significantly different at eachsublethal concentration with the two acaricides (P40:05).

The mean numbers of immatures produced weredrastically different with the two acaricide treatments.After exposure to fenpyroximate, the numbers declined asthe concentration increased, whereas very few immatureswere observed when exposed to pyridaben, even at thelowest pyridaben concentration (LC10 level) tested(Table 1). The proportion of eggs developed to immatures(viable eggs) was slightly smaller with fenpyroximate(0.30–0.43) than in the untreated controls (0.36–0.48),demonstrating that the effect of fenpyroximate wasminimal on the egg hatchability. These reproductivebioassays indicated that the impact of chronic exposure

to pyridaben was huge for both the numbers of eggs andimmatures produced, but fenpyroximate affected the eggproduction only.

3.3. Instantaneous rate of increase ðriÞ and effective median

concentration ðEC50Þ

All the RS ri estimates calculated using the total numbersof eggs counted 3 days after the treatment were signifi-cantly smaller than for the untreated control, with theexception of fenpyroximate at the LC10 treatment(Po0:05), and declined in a concentration-dependentmanner over all the residual days (fenpyroximate F ¼

13:72, df ¼ 2, 42, P ¼ 0:008; pyridaben F ¼ 14:23, df ¼ 2,42, P ¼ 0:001) (Fig. 2). The reduction was always larger inthose treated with pyridaben compared to fenpyroximatewhen compared at the same sublethal concentration. Theresidual effects of fenpyroximate on the RS ri remainedconstant over all the residual days (F ¼ 0:25, df ¼ 4, 42,P ¼ 0:36), whereas the effect of pyridaben at LC30 and LC50

increased significantly as the residual days stage increased.The concentration and residual day interacted significantly intheir effects on the RS ri (Po0:05) for both acaricides.The SP ri estimates incorporating the survivors of eggs

on the population growth were completely differentbetween the two acaricides (Fig. 3). The changes in the

ARTICLE IN PRESS

Table 1

Effects of residue days and sublethal concentrations of fenpyroximate and pyridaben on the offspring (eggs and immatures) productiona of Tetranychus

urticae. Each acaricide was tested on 30 adult females 1-, 3-, 5-, 7- and 9-days after application to the plant

Residue day No. eggs/female at No. immatures/female at

Control LC10 LC30 LC50 Control LC10 LC30 LC50

Fenpyroximate

1 8.271.1a 8.171.2a 5.271.6b 4.170.8b 3.370.5a 3.470.2a 2.470.6b 1.970.4b

3 8.070.8a 8.271.2a 5.270.7b 4.670.3b 3.870.3a 3.370.8b 2.370.5b 2.070.2b

5 7.971.3a 7.370.7a 5.471.1b 3.470.8b 3.370.3a 3.170.1a 1.970.3b 1.570.4b

7 8.371.3a 7.270.9a 4.270.9b 3.371.1b 2.970.2a 2.470.2a 1.670.4b 1.270.3b

9 8.270.9a 7.970.5a 4.970.6b 3.971.4b 3.870.6a 3.970.2a 1.570.1b 1.570.4b

Pyridaben

1 8.671.8a 4.970.4b 2.070.3c 1.270.3c 3.270.2a 0.070.0b 0.070.0b 0.070.0b

3 8.270.7a 5.570.8b 3.570.4c 2.670.4c 3.470.3a 0.170.0b 0.070.0b 0.070.0b

5 7.970.6a 4.370.4b 2.670.3c 1.870.3c 3.670.3a 0.070.0b 0.170.1b 0.070.0b

7 8.371.0a 4.570.3b 2.770.7c 1.370.1c 3.270.7a 0.070.0b 0.070.0b 0.070.0b

9 8.470.6a 4.970.8b 3.770.4b 2.270.1c 3.370.3a 0.170.1b 0.070.0b 0.070.0b

Means within rows followed by the same letter are not significantly different at P ¼ 0.05 by Tukey’s HSD test after a significant ANOVA. Residue effects

for both acaricides are not significant at any of the sublethal concentrations (Po0.05).aMean numbers of eggs and immatures were estimated, based on the cumulative numbers of live adult females at 3 and 6 days after treatment,

respectively.

Fenpyroximate

Residue day0 2 4 6 8 10

Inst

anta

neo

us

rate

of

incr

ease

(r i

)

0.4

0.6

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1.2

1.4 LC10 (6.4 ppm)LC30 (20.7 ppm)

LC50 (46.6 ppm)

Control

Pyridaben

Residue day0 2 4 6 8 10

Inst

anta

nan

eou

s ra

te o

f in

crea

se (

r i)

0.4

0.6

0.8

1.0

1.2

1.4LC10 (2101.8 ppm)

LC30 (8059.0 ppm)

LC50 (20446.5 ppm)

Control

Fig. 2. Change in the instantaneous rate of increase for the reproduction of survivors (RS ri) in Tetranychus urticae populations, starting with populations

originally consisting of 10 adult females, after exposure to various residue ages and sublethal concentrations of fenpyroximate or pyridaben. The dashed

horizontal line indicates the mean RS ri value of the untreated control.

M. Kim et al. / Crop Protection 25 (2006) 542–548546

SP ri with fenpyroximate were virtually identical to thoseobserved in the RS ri : sublethal effects (F ¼ 10:17, df ¼ 2,42, P ¼ 0:002) and residual effects (F ¼ 0:15, df ¼ 4, 42,P ¼ 0:12), but the values with pyridaben were alwaysnegative (�0.3838 to �0.0372), indicating that the popula-tions were considerably in decline. These results clearlydemonstrated that the profound impact of pyridaben onT. urticae population growth caused by the egg mortality,rather than egg production.

The effective concentrations (EC50s) that reduced the RSri by 50% remained constant with fenpyroximate, butgradually increased with pyridaben as the residual daystages increased (Table 2). Subsequently, the probit values(adult mortality from 72-h bioassay) solved for the EC50

concentrations into the LCx’s were significantly differentbetween fenpyroximate and pyridaben. The EC50s for

fenpyroximate were equivalent to 71–76% adult mortal-ities, whereas the values for pyridaben were equivalent to33–69%.Similar to the EC50s in the RS ri, the EC50s of the SP ri

for fenpyroximate were always higher than the LC50s overthe range of residual days, but the differences in the EC50

and LC50 in the SP ri were relatively in decline (Table 2).The corresponding adult mortalities for the EC50 estimatesranged from 60% to 71%. Estimation of the pyridabenEC50s in the SP ri was not feasible because too few eggsdeveloped immatures with the concentrations tested.

4. Discussion

The assessment of effects of pesticide based solely onacute toxicity estimates of T. urticae adults will lead to

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Pyridaben

Residue day0 2 4 6 8 10

Inst

anta

neo

us

rate

of

incr

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(ri)

-0.5

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-0.3

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-0.1

0.0

0.1

0.2

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0.5

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0.7

LC10 (2101.8 ppm)

LC30 (8059.0 ppm)

LC50 (20446.5 ppm)

Control

Fenpyroximate

Residue day0 2 4 6 8 10

Inst

anta

neo

us

rate

of

incr

ease

(r i

)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

LC10 (6.4 ppm)

LC30 (20.7 ppm)

LC50 (46.6 ppm)

Control

Fig. 3. Change in the instantaneous rate of increase for the survivors of progeny (SP ri) in Tetranychus urticae, starting with populations

originally consisting of 10 adult females, after exposure to various residue ages and sublethal concentrations of fenpyroximate or pyridaben. The dashed

horizontal line indicates the mean RS ri value of the untreated control. The shaded area in the graphic panel for pyridaben indicates that the RS ri values

were below 0.

Table 2

Median effective concentration (EC50a) on the instantaneous rate of increases (ri) based on the reproduction of survivors (RS) and survivors of progeny

(SP), with the corresponding predicted acute probit mortality for Tetranychus urticae exposed to fenpyroximate and pyridaben at various residue days

Residue day RS ri SP ri

EC50 (ppm) Probit mortality (%) EC50 (ppm) Probit mortality (%)

Fenpyroximate

1 114.6 71 116.2 71

3 131.1 74 99.0 68

5 130.8 74 72.7 60

7 124.0 73 70.1 60

9 253.7 76 104.0 69

Pyridaben

1 9118.1 33 —b —

3 19162.1 48 — —

5 19439.6 48 — —

7 19425.1 48 — —

9 49880.7 69 — —

aEC50 value was estimated using Eq. (2).bCannot be determined because too few immatures were observed to estimate the EC50 at any sublethal concentration.

M. Kim et al. / Crop Protection 25 (2006) 542–548 547

erroneous conclusions about a response at the certainpopulation levels, as the acute toxicities have incompleteendpoints for evaluating the total effects of the acaricideson T. urticae (Stark and Wennergren, 1995; Stark et al.,1997). McNair et al. (1995) argued that what happens to anindividual does not necessarily translate into effects at thepopulation level; our results in T. urticae clearly supportthis view. In this study, fenpyroximate and pyridabenexhibited completely different activities on the T. urticae

populations, even though they share the same mode ofaction, METI. The result from the current study isconsistent with that of Stark et al. (1997) who reportedthat T. urticae and a predatory mite species, Iphiseius

degenerans Berlese, with remarkably similar acute suscept-ibility to dicofol and neemix, exhibited completely different

patterns of susceptibility when the population growth wasthe endpoint evaluated.The persistenc of acaricides, along with their sublethal

effect, on T. urticae may sometimes be as important as thedirect toxicity in contributing to crop protection. Combin-ing the lethal and sublethal effects it is possible to predictthe total effects of pesticides at the population level.However, information on how the sublethal effects andpersistency of fenpyroximate and pyridaben affectT. urticae populations is sparse, as most studies havefocused on the resistant management of the spider mitespecies (Goka, 1998; Devine et al., 2001; Nauen et al., 2001;Stumpf and Nauen, 2001). In this study, T. urticae

exhibited completely different patterns of susceptibility tothe same sublethal concentrations of the acaricides when

ARTICLE IN PRESSM. Kim et al. / Crop Protection 25 (2006) 542–548548

the instantaneous rate of increase (ri) was the endpointevaluated (Figs. 2 and 3). These indicated that singletoxicity data were inappropriate to describe the total effectsof acaricides on T. urticae, especially if the acaricidesexhibited stage-specific activity.

Demographic toxicology has become quite an acceptedapproach, whereby the ecological and toxicological para-meters are combined with the assumption that predictionsof the total effects of toxins can be elucidated at thepopulation level (Walthall and Stark, 1997; Hansen et al.,1999). The reproductive bioassay presented in this studycan be used to evaluate the effects of acaricides with a highdegree of realism, especially for those differently affectingT. urticae populations. Pyridaben exhibited strong residualand sublethal effects on both of the reproduction and eggviability at low concentrations, while fenpyroximateaffected only the reproduction (Table 2; Figs. 2 and 3).These findings provide baseline information for theapplication of tactics for fenpyroximate and pyridabenagainst T. urticae in greenhouses or in the field. Because theefficacies of fenpyroximate and pyridaben are under threat(Cho et al., 1995; Stumpf and Nauen, 2001), a treatmentschedule for these chemicals should be carefully managedto reduce the risk of rapid resistance development. Theresistance management guidelines given for the METIacaricides by the Insecticide Resistance Action Committee(IRAC) should be strictly followed: only a single applica-tion of one METI-compound per season is recommendeddue to the high risk for increasing widespread METIresistance in T. urticae (Wege and Leonard, 1994; Stumpfand Nauen, 2001).

For a practical approach, an effective population controlof T. urticae can be achieved within a short time by thealternative treatment of low pyridaben concentrationstogether with non-METI acaricides that show no signs ofcross-resistance to the METIs. A recommended concentra-tion of fenpyroximate can be alternatively rotated with thenon-METI acaricides, as the resistance level in Korea ofT. urticae to fenpyroximate (10.6-fold) was much lower thanthat of pyridaben (120.4-fold) (Kim, 2002). If alternativerotation partners are not available, fenpyroximate andpyridaben could be restrictively rotated once in a singleseason because no cross-resistance between fenpyroximateand pyridaben has been observed in Korea (Kim, 2002).

Acknowledgments

We thank Joon-Ho Lee (Seoul National University,Seoul, Korea) and Brian L. Strom (USDA, Forest Service,Pineville, USA) for their helpful comments on the earlierdraft of the manuscript.

References

Allison, P.D., 1995. Survival Analysis Using the SAS System: A Practical

Guide. SAS Institute, Cary, NC, USA.

Cho, J.R., Kim, Y.J., Ahn, Y.J., Yoo, J.K., Lee, J.O., 1995. Monitoring of

acaricide resistance in field-collected populations of Tetranychus

urticae (Acari: Tetranychidae) in Korea. Korean J. Appl. Entomol.

34, 40–45.

Dekeysers, M.A., Downer, R.G.H., 1994. Biochemical and physiological

targets for miticides. Pestic. Sci. 40, 85–101.

Devine, G.J., Barber, M., Denholm, I., 2001. Incidence and inheritance of

resistance to METI-acaricides in European strains of the two-spotted

spider mite (Tetranychus urticae) (Acari: Tetranychidae). Pest Manag.

Sci. 57, 443–448.

Goka, K., 1998. Mode of inheritance of resistance to three new acaricides

in the Kanzawa spider mite, Tetranychus kanzawai Kishida (Acari:

Tetranychidae). Exp. Appl. Acarol. 22, 699–708.

Haanstra, L., Doelman, P., Oude Voshaar, J.H., 1985. The use of

sigmoidal dose response curves in soil ecotoxicological research. Plant

Soil 84, 293–297.

Hansen, F., Forbes, V.E., Forbes, T.L., 1999. Using elasticity analysis of

demographic models to link toxicant effects on individuals to the

population level: an example. Funct. Ecol. 13, 157–162.

Hirata, K., Kawamura, Y., Kuno, M., Igarasgi, H., 1995. Development of

a new acaricide, pyridaben. J. Pest. Sci. 20, 177–179.

Kammenga, J., Laskowski, R., 2000. Demographic in Ecotoxicology.

Wiley, New York.

Kerns, D.L., Stewart, S.D., 2000. Sublethal effects of insecticides on the

intrinsic rate of increase of cotton aphid. Entomol. Exp. Appl. 94,

41–49.

Kim, M., 2002. Ecotoxicological evaluation of pesticide effect: response of

Tetranychus urticae and, two predatory mite species, Amblyseius

womersleyi and Phytoseiulus persimilis, to fenpyroximate and pyrida-

ben. M. S. Thesis, Korea University, Korea, Seoul, p 85.

McNair, J.B., Goulden, C.E., Ziegenfuss, M.C., 1995. Is there a place for

ecotoxicology? SETAC News 15, 18–21.

Nauen, R., Stumpf, N., Elbert, A., Zebitz, C.P.W., Winkler, V., 2001.

Acaricide toxicity and resistance in larvae of different strains of

Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae). Pest

Manag. Sci. 57, 253–261.

Parrella, M.P., Jones, V.P., 1987. Development of integrated pest

management strategies in floricultural crops. Bull. Entomol. Soc.

Am. 33, 28–34.

Robertson, J.L., Worner, S.P., 1990. Population toxicology: suggestions

for laboratory bioassays to predict pesticide efficacy. J. Econ.

Entomol. 83, 8–12.

SAS Institute, 1996. SAS/STAT Guide for Personal Computers, version

6.3 ed. SAS Institute, Cary, NC.

Shapiro, S.S., Wilk, M.B., 1965. An analysis of variance test for normality

(complete samples). Biometrika 52, 591–611.

Sim, C., 2000. Genetics and fitness of Tetranychus urticae (Acari:

Tetranychidae) resistance to fenpyroximate and pyridaben. M. S.

Thesis, Korea University, Seoul, Korea.

Stark, J.D., Wennergren, U., 1995. Can population effects of pesticides be

predicted from demographic toxicological studies? J. Econ. Entomol.

88, 1089–1096.

Stark, J.D., Tanigoshi, L., Bounfour, M., Antonelli, A., 1997. Reproduc-

tive potential: its influence on the susceptibility of a species to

pesticides. Ecotoxicol. Environ. Saf. 37, 273–279.

Stumpf, N., Nauen, R., 2001. Cross-resistance, inheritance, and biochem-

istry of mitochondrial electron transport inhibitor-acaricide resistance

in Tetranychus urticae (Acari: Tetranychidae). J. Econ. Entomol. 94,

1577–1583.

Walthall, W.K., Stark, J.D., 1997. Comparison of two population-level

ecotoxicological endpoints: The intrinsic (rm) and instantaneous (ri)

rates of increase. Environ. Toxicol. Chem. 16, 1068–1073.

Wege, P.J., Leonard, P.K., 1994. Insecticide resistance action committee

(IRAC) fruit crops spider mite resistance management guidelines 1994.

In: Proceeding of the Brighton Crop Protection Conference–Pest and

Disease, pp. 427–430.