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Crop Protection 48 (2013) 29e34

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Crop Protection

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Sublethal and transgenerational effects of chlorantraniliprole onbiological traits of the diamondback moth, Plutella xylostella L.

Lei Guo a, Nicolas Desneux b, Shoji Sonoda c, Pei Liang a,*, Peng Han b, Xi-Wu Gao a

aDepartment of Entomology, China Agricultural University, Beijing 100193, Chinab French National Institute for Agricultural Research (INRA), ISA, 400 route des chappes, 06903 Sophia-Antipolis, Francec Institute of Plant Science and Resources, Okayama University, Kurashiki, Okayama 710-0046, Japan

a r t i c l e i n f o

Article history:Received 13 August 2012Received in revised form14 February 2013Accepted 15 February 2013

Keywords:Sublethal effectBiological traitsIntrinsic rate of increaseRyanodine receptorDiamide insecticide

* Corresponding author. Tel./fax: þ86 10 62731306E-mail address: liangcau@cau.edu.cn (P. Liang).

0261-2194/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.cropro.2013.02.009

a b s t r a c t

The diamondback moth, Plutella xylostella (L.), is an important international pest of cruciferous vegeta-bles. The effects of the new diamide insecticide chlorantraniliprole, at a lethal concentration inducingonly 25% mortality (LC25), were assessed on the development and reproductive parameters of P. xylostellaunder laboratory conditions. In addition, effects on development time, pupation rate, larval and pupaeweight, fertility, and survival in the parent and F1 generations were assessed. When 4th instarP. xylostella larvae were exposed to LC25 of chlorantraniliprole on a cabbage (Brassica oleracea var.capitata L.) leaf for 96 h, we observed increased developmental time for 4th instar larval to pupa period(4.27 days vs. 3.34 days in the control), lower pupal weight (3.58 mg vs. 4.17 mg in the control) anddecreased adult fecundity (by 42%). F1 generation underwent transgenerational effects, i.e. higherdevelopmental time from egg to pre-pupae and lower egg hatching rate occurred. Demographic growthparameters, such as the net reproductive rate (R0), the intrinsic rate of increase (rm), and finite rate ofincrease (l) were significantly lower for the LC25 chlorantraniliprole treated group than for the untreatedcontrol. Our results suggest that exposure to LC25 of chlorantraniliprole may have negative effects bothon exposed individuals and on subsequent generations in P. xylostella.

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1. Introduction

The diamondback moth (DBM), Plutella xylostella (L.), is a majorworldwide pest in cruciferous vegetables (Talekar and Shelton,1993; Fathi et al., 2011; Zalucki et al., 2012). Larvae feed onvarious plants in the crucifer family, both in field (e.g. canolaBrassica campestris L., mustard Brassica juncea (L.), cabbage Brassicaoleracea L., cauliflower B. oleracea L. and kohlrabi B. juncea Coss) andin greenhouse crops (Zhang et al., 2012). The management of DBMrelies primarily on broad spectrum chemical insecticides in mostcropping systems, though natural enemies could be used in thegreenhouse (Tabone et al., 2010, 2012). Unfortunately, most of theexisting insecticides are harmful to the environment and multiplepotential side effects on beneficial arthropods have been observed(Desneux et al., 2007; Biondi et al., 2012b; Lu et al., 2012). Inaddition, because of the extensive use of commercial insecticidesand inappropriate applications of the pesticides, DBM has devel-oped resistance to at least 79 insecticides, including organophos-phates, carbamates, pyrethoids, abamectin, spinosad and Bacillus

.

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thuringiensis-based products (Talekar and Shelton,1993; Tabashnik,1994; Sun et al., 2012). This is due to its high fecundity rate,reproductive potential and rapid turnover of generations in crops.

Chlorantraniliprole, an insecticide from the class of ryanodinereceptor modulators, is an extremely potent chemical againstlepidopteran pests, including those that are resistant to other cat-egories of insecticides (Cordova et al., 2006). In addition, it is highlyselective for insect over mammalian ryanodine receptors. Onceingested, chlorantraniliprole activates the release of internal cal-cium, leading to a halt in feeding, lethargy, muscle paralysis and,ultimately, to the death of the insect (Lahm et al., 2005). Thesecharacteristics have made chlorantraniliprole a promising tool ininsecticide resistance management. Since 2008, chlorantraniliprolehas been registered in China for use in several crops against larvallepidopteran pests (P. xylostella, Spodoptera exigua Hübner, Lith-ocolletis ringoniellaMatsumura, Carposina nipponensisWalsingham,Chilo suppressalis Walker and Cnaphalocrocis medinalis Güenée).The concentrations of pesticides on treated plants are known tovary (Koppenhofer and Fuzy, 2008; Biondi et al., 2012a; Han et al.,2012), notably according to how often the products are applied andhow fast the active ingredients deteriorate (after application)because of biotic and abiotic factors (Desneux et al., 2005).

L. Guo et al. / Crop Protection 48 (2013) 29e3430

Therefore, chlorantraniliprole concentrations would vary in fieldand greenhouse conditions. DBM is likely to be exposed to in-secticides at low and/or sublethal concentrations of chloran-traniliprole in treated agro-ecosystems, which may result inmultiple sublethal effects (see Desneux et al., 2007 for a thoroughreview). Sublethal effects of insecticides could affect populationdynamics (Stark and Banks, 2003) through impairment to behav-ioural and physiological traits (Desneux et al., 2004a, 2004b; Arnoand Gabarra, 2011; Stara et al., 2011). Moreover, studies havedemonstrated that exposure to insecticides could affect insectlongevity and fecundity (Desneux et al., 2006; Bao et al., 2009;Liang et al., 2012; Liu et al., 2012). To date, possible sublethal effectsof chlorantraniliprole on insects have only been sparsely docu-mented (Hannig et al., 2009; Campos et al., 2011; Biondi et al.,2012a) despite the fact that understanding such effects would becrucial to both risk assessment of chlorantraniliprole on non-targetspecies and to the overall effects of the insecticide on the varioustargeted pests.

To further the understanding of the global effects of chloran-traniliprole on DBM and, therefore, to optimize Integrated PestManagement (IPM) programs involving the use of chloran-traniliprole on this pest, the sublethal activity of this insecticide onDBM are required to be described accurately and thoroughly. Theobjectives of the present study were to record such effects on thebiological characteristics of DBM. We assessed the effects of a lowlethal concentration (LC25) of chlorantraniliprole directly onexposed individuals, the parent generation, as well as the trans-generational effects that are without direct exposure to the insec-ticide in the subsequent generation (F1). The results were used toevaluate the impact of chlorantraniliprole on the demographicparameters of DBM e.g. intrinsic rate of increase.

2. Materials and methods

2.1. Insects

The DBM strain used in the tests was reared in our laboratory forover ten years using vermiculite cultured radish (Raphanus sativusL. var. cuiqing) seedlings. Over thirty thousand individuals werereared in each generation to ensure there was not a strong geneticbottleneck. All stages of the DBM were maintained in climaticchambers (27 � 1 �C, 80 � 10% RH, 16:8 L:D).

2.2. Insecticide, insecticide exposure and chlorantraniliprole LC25estimate

Technical grade 95% chlorantraniliprole was obtained fromDuPontAgricultural Chemicals Ltd., Shanghai, China. Bioassayswereconducted using a leaf-dip method slightly adapted from themethods of Liang et al. (2003) and He et al. (2012). Cabbage(B. oleracea var. capitata L.) leaves measuring 6 � 6 cm wereimmersed for 10 s in various concentrations of chlorantraniliproleprepared with distilled water containing 1 g L�1 Triton X-100. Theleaveswere left to air dry for 1.5 h andwere thenplaced individuallyinto a Petri dish lined with filter paper. A total of 15 first day fourth-instar larvae were introduced into each dish, and three replicateswere prepared per concentration tested. Five concentrations ofchlorantraniliprole, ranging from 0.005 to 0.1 mg L�1, and onecontrol (distilled water with 1 g L�1 Triton X-100) were tested ineach bioassay. Mortality was assessed after 96 h of exposure tochlorantraniliprole. Individuals that did not move when pushedgentlywith a brushwere then recordedas dead. The LC25 value, usedin subsequent experiments, was calculated using PoLoPlus 2.0software (LeOra Software, Petaluma, CA). The concentrationemortality relationship (data corrected for control mortality) was

considered valid i.e. it fitted the observed data when there wasabsence of significant deviation between the observed and the ex-pected mortality (P > 0.05) (Robertson and Preisler, 1992).

2.3. Impact of LC25 chlorantraniliprole on biological traits in DBMparent generation

DBM 4th instar larvae were exposed to the LC25 of chloran-traniliprole (we actually used the upper limit of LC25 estimate,20.25 mg L�1; see Results section); these exposed individuals arehereafter named the parent generation. Cabbage leaves were dip-ped in the LC25 chlorantraniliprole solution or in the control solu-tion (distilled water with 1 g L�1 Triton X-100). The treated leaveswere cut into 6 cm disks and put into a plastic Petri dish after beingair-dried at room temperature for 2 h. Fifteen DBM neonate 4thinstar larvae (4th instar for <3 h) were then introduced into thePetri dish. Each treatment and control was replicated six times. Thelarvae were left to feed until they developed into pupae. Thechlorantraniliprole-treated leaves were changed every two days.The Petri dishes containing the treated larvae were placed in cli-matic chambers (27 � 1 �C, 80 � 10% RH, 16:8 L:D). We recorded (i)the duration of development, (ii) the numbers of survivors atdifferent development stages, and (iii) the weight of individualswhen the DBM 4th instar larvae were 2-day old. After pupation, ten2-day old pupae per replicate were randomly chosen and weighed.All pupae were then placed back into the climatic chambers untilthe adults emerged.

Adults previously collected were used to assess sublethal effectsof chlorantraniliprole at the adult stage. Five couples (one male andone female of the same age) were introduced into a cylindricalplastic cage (8.8 cm diameter, 21.2 cm high), and the bottom of thecage was covered with one layer of fresh cabbage leaves. The topend of the cage was covered with nylon net and a vial containing10% sugar solution closed by a cotton bud that was fixed on the netto supply food to the DBM adults. A total of six replicates (cages) pertreatment, i.e. chlorantraniliprole at LC25 and control, were used.The leaves were replaced every day until the number of DBM eggslaid per female per day was below five; male and female longevitywas recorded. The eggs laid on the leaves were counted daily andthe leaves were then placed into a 9 cm plastic Petri dish (in cli-matic chambers at 27 � 1 �C, 80 � 10% RH, 16:8 L:D) for furtherobservation of F1 individuals (see below).

2.4. Transgenerational sublethal effects of chlorantraniliprole inDBM F1 individuals

To investigate the sublethal effects of chlorantraniliprole on theF1 generation, the ratio of hatching, mortality, fecundity and thedevelopmental time of eggs, larvae and pupae were recorded.Batches of one hundred eggs (representing one replicate) werechecked daily and the eggs were considered dead when they didnot hatch after five days. Five replicates were performed for eachtreatment (chlorantraniliprole and control). Thirty neonate larvae,that hatched the same day from the treatments, were placed in aPetri dish containing a piece of cabbage leaf until they developedinto pupal stage. The hatched larvae were supplied with a cabbageleaf and maintained in climatic chambers (27 � 1 �C, 80 � 10% RH,16:8 L:D). The leaves were changed daily during all the develop-ment cycle and the survival rate during the larval and pupal stageswere recorded.

2.5. Biological and demographic parameters

The possible impact of the LC25 of chlorantraniliprole on DBMdemography (potential population growth) was assessed using the

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Larvae (4th instar) Pupae

Mea

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mg)

ControlChlorantraniliprole

** ***

Fig. 1. Body weight of larvae and pupae of Plutella xylostella (mean � SD) afterexposure to LC25 of chlorantraniliprole (or water with 1 g L�1 Triton X-100 for thecontrol) the time they were early fourth instar. **P < 0.01, ***P < 0.01 (significantdifference with the respective control, t-test).

L. Guo et al. / Crop Protection 48 (2013) 29e34 31

fertility span tables generated from the assays. Pairs of DBM adult(control n ¼ 25, chlorantraniliprole-treated n ¼ 22) were randomlychosen. The intrinsic rate of increase (rm) was shown to be a moreaccuratemeasure of toxic effect than lethal concentration estimates(Forbes and Calow, 1999). The time from oviposition to emergence,i.e. time from egg to adult, adult survival rate, daily fecundity andsex ratio in the F1 generation individuals was used to estimate thefollowing demographic growth parameters:

1. Net reproductive rate (R0¼P

lxmx): the population growth rateper generation with regard to the number of female offspringproduced per female (Deevey, 1947); lxmx where x is the age ofthe cohort; lx is the proportion of individuals surviving to age x,and mx is the number of females produced per female of age x.

2. Mean generation time (T ¼ Pxlxmx/R0): the average interval

separating births from one generation to the next (Deevey,1947).

3. The intrinsic rate of increase (rm): the maximum exponentialincrease rate in a population growing within defined physicalconditions (Birch, 1948). The growth rate is calculated by iter-atively solving the equation: 1 ¼ P

lxmx exp(�rmx).4. Finite rate of increase, l ¼ exp(rm): the factor by which a

population multiplies (Birch, 1948).5. Population doubling time, Dt ¼ ln(2)/rm: the time required by a

population, when growing exponentially, to double when itincreases at a given rm (Carey, 1989).

2.6. Data analysis

Datasets were first tested for normality and homogeneity ofvariance using the KolmogoroveSmirnov and the Cochran testsrespectively and were transformed if necessary. The datasets weresubjected to t-test to compare chlorantraniliprole-exposed groupsto respective control groups.

3. Results

3.1. LC25 of chlorantraniliprole

Mortality in all control groups was always below 5%. Theregression analysis indicated a strong negative correlation(r2 ¼ 0.9698) between the concentration logarithm of chloran-traniliprole and probit of larvae mortality. Because no significantdeviation between the observed and the expected data was noted,the concentrationemortality relationship was considered valid andLC25 of chlorantraniliprole was calculated as 13.84 mg L�1 (with a95% confidence interval of 6.88e20.25 mg L�1). The upper limit ofLC25 (20.25 mg L�1) was used to treat the insect in the subsequentexperiments. Indeed, when 4th instar DBM larvae were exposed to20.25 mg L�1 of chlorantraniliprole for 96 h (i.e. the upper limit ofthe estimated LC25 of chlorantraniliprole), corrected mortality was24.47%, i.e. it matched the mortality that we targeted to carry outthe following bioassays.

3.2. Direct effects of chlorantraniliprole on development time andweight

The body weight of the larvae exposed to chlorantraniliprolewas significantly lower than in the untreated control (Fig. 1,t ¼ 8.361, P ¼ 0.0001). Similarly, the body weight of the pupae inchlorantraniliprole-treated group was significantly lower than inthe control (t ¼ 3.311, P ¼ 0.0079). The development time of theinsects from 4th instar larvae to pupae was delayed after exposureto chlorantraniliprole (4.27 � 0.18 days) vs. control (3.34 � 0.15

days) (t ¼ 9.722, P < 0.0001), while the development from pupa toadult was not affected (chlorantraniliprole: 3.24 � 0.35 days, con-trol: 3.28 � 0.20 days, t ¼ 0.2431, P ¼ 0.8129).

3.3. Direct and transgenerational effects on fecundity, egg hatchingand adult longevity

The LC25 of chlorantraniliprole significantly decreased fecundityby 42% in the parent generation (Fig. 2A, t ¼ 6.956, P < 0.0001) butthis effect was not observed in the F1 generation (t ¼ 1.083,P ¼ 0.3041). The hatching of eggs laid by chlorantraniliprole-exposed individuals was not significantly different from controlindividuals (Fig. 2B, t¼ 1.062, P¼ 0.3130), but hatching of those laidby the individuals of the F1 generation was significantly decreasedwhen parents had been exposed to the LC25 of chlorantraniliprole(t ¼ 2.903, P ¼ 0.0158). The longevity of males in the treated groupwas significantly shortened by nearly two days in the parent gen-eration (Fig. 3A) and 1.5 days in the F1 generation, respectively(Fig. 3B, Parent: t ¼ 8.446, P < 0.0001, F1: t ¼ 2.444, P ¼ 0.0346).However, the longevity of the female adults was not affected inboth parent and F1 generations (Parent: t ¼ 2.058, P ¼ 0.0667, F1:t ¼ 1.878, P ¼ 0.0898).

3.4. Transgenerational effects on development and survival of DBMin F1

When the parents were exposed to chlorantraniliprole, thedevelopment of their eggs in the F1 generation took significantlymore time (Table 1, P < 0.01). In addition, the development cycle ofthe third and fourth instar larvae was also increased (P < 0.05),though the first and second instar larvae were not significantlyaffected (P > 0.05). Lastly, the length of time for pupa to develop inthe chlorantraniliprole-treated group was similar to that of theuntreated group (Table 1). Despite the fact that they had never beendirectly exposed to chlorantraniliprole, total mortality of larvae inthe offspring (F1 generation) of individuals that had been exposedto LC25 of chlorantraniliprole (parent generation) was significantlyincreased (Table 2, P < 0.05).

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Fig. 2. (A) Fecundity of Plutella xylostella females (mean number � SD of eggs laid per female) from the parent generation i.e. exposed to LC25 of chlorantraniliprole, and from thesubsequent generation (F1), i.e. never exposed directly to chlorantraniliprole. (B) Percentage of eggs that hatched in parent and F1 population when exposed or not to LC25 ofchlorantraniliprole. ***P < 0.001, *P < 0.05 (significant difference with the respective control, t-test), ns: not significantly different with the respective control.

L. Guo et al. / Crop Protection 48 (2013) 29e3432

3.5. Effect of chlorantraniliprole on DBM biological anddemographic parameters

When compared to the control population, the net reproductionrate (R0), the intrinsic rate of natural increase (rm) and the finite rateof increase (l) decreased significantly by 30%, 12% and 4% (respec-tively) in a population that was exposed to chlorantraniliprole (allP < 0.001; Table 3). In addition, both population doubling time (Dt)and generation time (T) did increase significantly (all P < 0.001) inchlorantraniliprole-treated population when compared to thecontrol.

4. Discussion

Chlorantraniliprole is a potent activator of the ryanodine re-ceptors which may release stored calcium from the sarcoendo-plasmic reticulum to lumen. The release and depletion of internalcalcium stores in muscles cause insect mortality in the end through

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ns

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Fig. 3. Mean longevity in days (�SD) of Plutella xylostella female and male adults after expostransgenerational exposure respectively. The control group received only distilled water witwith the respective control, t-test), ns: not significantly different with the respective contr

starvation and paralysis (Cordova et al., 2006). Chlorantraniliprole,belonging to a recent class of insecticide, is effective against a broadrange of lepidopteran pests including P. xylostella, Spodoptera fru-giperda (J.E. Smith) andHeliothis virescens (F.) with LC50 from0.01 to0.03 ppm (Lahm et al., 2005). Since it was registered in China in2008, this new insecticide has been extensively used to controlmany lepidopteran insects, especially P. xylostella. However, itscurrent extensive use on P. xylostella may lead to a relatively rapidselection of resistant populations in the field (Hu et al., 2010; Wangand Wu, 2012). This suggests the need to provide information thatwould enable optimal use of this new insecticide to manage DBMin crops. Our study has demonstrated that a low concentration ofchlorantraniliprole (LC25) can negatively affect various life traitsof DBM population, not only through direct sublethal effects inexposed individuals, in particular slower larval developmentand decreased adult fecundity, but also through transgenerationaleffects on F1 individuals that were never directly exposed tothe insecticide. Such effects shown to drastically impact key

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ure to LC25 of chlorantraniliprole in the parent (A) and F1 (B) generations, i.e. direct andh 1 g L�1 Triton X-100 (see M&M section). ***P < 0.001, *P < 0.05 (significant differenceol.

Table 3Biological and demographic parameters of Plutella xylostellawhen exposed to LC25 ofchlorantraniliprole (n ¼ 22). The control group (n ¼ 25) received only distilled waterwith 1 g L�1 Triton X-100 (seeM&M section). The values (mean� SD) in bold text aresignificantly different when compared to respective control (t-test).

Demographic parameters Control Treatment Statistics

P t df

Net reproduction rate: R0 96.03 � 6.64 67.45 � 8.06 <0.0001 13.33 45Finite rate of increase: l 1.36 � 0.05 1.31 � 0.04 <0.0001 4.42 45Intrinsic rate of increase: rm 0.31 � 0.03 0.27 � 0.03 <0.0001 4.87 45Generation time: T (day) 14.65 � 0.46 15.74 � 0.43 <0.0001 8.43 45Doubling time: Dt (day) 2.26 � 0.11 2.60 � 0.10 <0.0001 11.29 45

Table 1Effect of LC25 of chlorantraniliprole on duration of pre-adult development of Plutellaxylostella from the F1 generation. The values (mean � SD) in bold text are signifi-cantly different when compared to respective control (t-test).

Developmentstage

Duration of development (days) Statistics

Control Treatment P t df

Egg 3.13 � 0.08 3.39 � 0.11 0.0038 4.03 8First instar 2.12 � 0.18 2.01 � 0.50 0.6499 0.47 8Second instar 1.85 � 0.20 1.92 � 0.45 0.7655 0.31 8Third instar 2.00 � 0.34 2.41 � 0.20 0.0489 2.32 8Fourth instar 3.07 � 0.42 3.70 � 0.32 0.0276 2.69 8Pupa 3.49 � 0.60 2.82 � 0.77 0.1628 1.54 8

L. Guo et al. / Crop Protection 48 (2013) 29e34 33

demographic growth parameters in DBM e.g. the intrinsic rate ofincrease rm, were significantly decreased in the chlorantraniliproletreated population.

The lethal and sublethal effects of chlorantraniliprole have beeninvestigated on many pests such as Anomala orientalisWaterhouse,Popillia japonica Newman, Cyclocephala borealis Arrow(Koppenhofer and Fuzy, 2008), Rhagoletis pomonella Walsh, Rha-goletis mendax Curran, Rhagoletis cingulata Loew (Teixeira et al.,2009), Lobesia botrana Denis & Schiffermüller (Ioriatti et al.,2009), Cydia pomonella Linnaeus (Knight and Flexner, 2007),S. exigua (Lai and Su, 2011), P. xylostella, S. exigua, Trichoplusia niHübner, Helicoverpa zea Boddie (Hannig et al., 2009) and Heli-coverpa armigera Hübner (Cao et al., 2010). Lai and Su (2011) re-ported that chlorantraniliprole at LC30 (6.7 mg L�1) and LC50(12.7 mg L�1) delayed S. exigua larval development when they sur-vived initial exposure. A similar effect was found in P. xylostella inthe present study (Table 2) and the mean body weight of fourthinstar larvae fed on LC25 of chlorantraniliprole treated cabbageleaveswas lower than those in the untreated control; consequently,the body weight of the pupae of the treated population was lowerthan that of the control one. This may be because after exposure tothe LC25 of chlorantraniliprole, the amount of leaves consumed bythe larvae decreased and there was not enough food ingested forthe larvae to grow optimally, so the bodyweight of subsequentpupae decreased.

Teixeira et al. (2009) reported that the low concentration ofchlorantraniliprole (500 mg L�1) mixed in the food had no effect onreproduction of three species of tephritid fruit flies. Lai and Su (2011)also found that the reproduction of S. exigua had not been affectedafter their neonate larvae were orally exposed to chlorantraniliproleat LC30 (6.7 mg L�1) and LC50 (12.7 mg L�1). However, we have shownthat treatment of 4th instar larvae of P. xylostellawith LC25 of chlor-antraniliprole could decrease adult fecundity by up to 42%. In variousstudies, reduced fecundity caused by various insect growth regula-tors in Ephestia kuehniellaZeller, S. exigua and L. botranawas linked tophysiological and morphological disturbances in both males andfemales (MarcoandVinuela,1994; Saenz-De-Cabezonet al., 2006). Inthe present study, a similar situation occurred but it was more likelydue to a lower food intakeduring the4th instar larva stage because of

Table 2Effect of LC25 of chlorantraniliprole onmortality rate of Plutella xylostella from the F1generation at various pre-adult stages of development and for the total larvaedevelopment. The values (mean � SD) in bold text are significantly different whencompared to respective control (t-test).

Developmentstage

Mortality (%) Statistics

Control Treatment P t df

First instar 3.94 � 2.68 14.06 � 5.02 0.0041 3.97 8Second instar 9.08 � 3.69 16.82 � 7.41 0.0698 2.09 8Third instar 12.38 � 6.53 15.16 � 11.61 0.6531 0.47 8Fourth instar 13.00 � 3.00 17.50 � 2.36 0.0298 2.64 8Total larvae stage 38.40 � 12.99 63.54 � 6.15 0.0110 3.29 8

chlorantraniliprole exposure. Similar results which only focused onthe same generation exposed to the lethal or sublethal concentra-tions of chlorantraniliprole had been reported in other insects(Hannig et al., 2009; Cao et al., 2010; Lai and Su, 2011). Nevertheless,we have reported for the first time that negative effects of chloran-traniliprole can also be passed on to the F1 generation (i.e. trans-generational effects). For example, thoughnodifference between thetreatment and control F1 populations was shown in fecundity, thelife span of the F1 extended remarkably, especially the develop-mental periods of eggs, the 3rd and 4th instar larvae (Table 2). Inaddition, in the F1 generation, larval mortality was higher in in-dividuals from the chlorantraniliprole-exposed parent generationthan in those from the control parent generation (Table 3).

The analyses of estimated demographic parameters inchlorantraniliprole-contaminated and untreated control pop-ulations have provided some insight on possible effects of chlor-antraniliprole on DBM on the generational scale. R0, rm and l valuesin the treated populationwere significantly lower than those in thecontrol one, whereas both the Tand Dt values were higher (Table 3).This suggests that the low LC25 concentration may suppress/slowdown DBM population growth, i.e. the use of chlorantraniliprolewould not likely result in DBM resurgence. By contrast, the horm-esis effect (Calabrese and Baldwin, 2003; Tan et al., 2012) was re-ported in DBMwhen exposed to the LC25 of fenvalerate (pyrethroidinsecticide) (Fujiwara et al., 2002) and the gross reproduction rateof the pest was increased when treated with the LC10 of hexa-flumuron (Mahmoudvand et al., 2011). Therefore, various positiveand/or negative effects of low lethal doses of pesticides may occurin DBM according to the toxic compound the pest is exposed to infield conditions.

To summarize, the present study indicated that the low con-centration of chlorantraniliprole inhibited the development oflaboratory reared DBM populations. This means that the applica-tion of this new insecticide on crops may control the pest in a veryeffective manner by both killing the insect and suppressing itspopulation growth, possibly more efficiently than other commonlyused insecticides. Interestingly enough, high levels of resistance tochlorantraniliprole have been reported in field populations of DBM(Wang and Wu, 2012) and we failed to select a chlorantraniliprole-resistant DBM population under laboratory conditions after con-ducting experiments for two years (Liang and Gao, unpublisheddata). Therefore, other factors may be at work under field condi-tions regarding the selection of a chlorantraniliprole-resistant DBMpopulation. Further studies should be carried out to assess thatissue, e.g. by using the comparative genomics method as well asusing both laboratory and field populations as test insects.

Acknowledgement

This work was supported by the National Basic Research andDevelopment Program of China (2012CB114103) and the NationalNatural Science Foundation of China (30971941 and 31171873).

L. Guo et al. / Crop Protection 48 (2013) 29e3434

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