HORTSCIENCE 42(2):285–288. 2007.

Efficacy of Spiromesifen AgainstGreenhouse Whitefly (Homoptera:Aleyrodidae) on StrawberryJ.L. Bi1 and N.C. ToscanoDepartment of Entomology, University of California, Riverside, CA 92521

Additional index words. Trialeurodes vaporariorum, Fragaria ananassa

Abstract. Spiromesifen is a novel insecticide (belonging to the new chemical class ofspirocyclic phenyl-substituted tetronic acids) with a unique mode of action. Laboratoryand field experiments were conducted to test the efficacy of this insecticide against thegreenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae)on strawberry, Fragaria ananassa (L.). Laboratory experiments showed that spirome-sifen at 0.5 and 1.0 mg�mL–1 a.i. inhibited egg hatching by 80% and 100%, respectively,whereas at concentrations of 3.1, 3.0, and 10.0 mg�mL–1 a.i., this insecticide, respectively,killed 100% of the first, second, and third instar nymphs. Much lower toxicity to adultswas observed. Field trials revealed that application of spiromesifen reduced the whiteflyegg numbers by 61% to 80% from 2 to 3 weeks posttreatment in comparison with thepyriproxyfen treatment, whereas the application lowered the egg numbers by 34% to73% from 2 to 5 weeks posttreatment compared with the buprofezin treatment. Incomparison with pyriproxyfen treatment, spiromesifen application decreased thenumbers of immature whiteflies by 29% to 92% from 1 to 6 weeks posttreatment. Theeffect of spiromesifen on reduction of immatures was similar to that of buprofezin. Also,the efficacy of spiromesifen on suppression of adult numbers was comparable to that ofpyriproxyfen or buprofezin. Spiromesifen shows promise for inclusion in integratedgreenhouse whitefly management programs and insecticide resistance managementprograms on strawberry.

California is a world leader in strawberryproduction. Since the late 1990s, strawberryproduction has been threatened by a majorinsect pest, the greenhouse whitefly, Tria-leurodes vaporariorum Westwood (Homo-ptera: Aleyrodidae) (Bi et al., 2002a, 2002b,2002c). This pest removes a large amount ofphloem sap from strawberry plants, resultingin decreased fruit yield and reduced fruitquality through reduction of glucose, citricacid, and vitamin C (Bi and Toscano, unpub-lished data; McKee and Zalom, 2007). Inaddition, this pest decreases the marketablevalue of strawberry fruits through honeydewand the associated sooty mold contamina-tions and transfers plant virus diseases (Biet al., 2002a, 2002b, 2002c; F. G. Zalom,pers. comm., 2005). Control of this pest inCalifornia has been heavily dependent onchemical insecticides, including neonicoti-noids, insect growth regulators, and someconventional insecticides.

Imidacloprid is a neonicotinoid insecti-cide, which acts on acetylcholine receptors inthe insect central nervous system with sys-

temic properties and long residual activityagainst sucking insects such as whiteflies(Kagabu, 1999; Ware, 2000; Yamamoto,1999). The residual activity in strawberryagainst the greenhouse whitefly is over2 months after soil application (Bi et al.,2002a, 2002b). Since its first emergencyregistration in 1999 under U.S. Environmen-tal Protection Agency Section 18 exemptionon strawberry in California, imidacloprid(trade name Admire) has been used mostintensively to control the whiteflies. Pyri-proxyfen is an insect growth regulator affect-ing the hormonal balance in insects andresulting in a strong suppression of embryo-genesis and adult formation (Ishaaya andHorowitz, 1998). Pyriproxyfen (trade nameEsteem) is very effective in inhibiting thewhitefly egg hatching after foliar spray andhas been registered on strawberry in Californiasince 2003 (Bi et al., 2002a, 2002b). Theuse of imidacloprid at transplanting in fallfollowed by the application of pyriproxifenin early spring provides the greatest controlof the whiteflies on strawberry (McKee andZalom, 2007). Commonly used conventionalinsecticides against whiteflies on strawberryinclude endosulfan (chlorinated hydrocar-bon), chlorpyrifos and malathion (organo-phosphate) , methomyl (carbamate) ,bifenthrin and fenpropathrin (pyrethroid)(Bi and Toscano, 2007). The residual activ-ities of these insecticides against the green-house whitefly on strawberry are �1 week.Application of these insecticides is onlyrecommended to suppress high adult whitefly

populations in mid or late season after theefficacy of imidacloprid or pyriproxyfenapplied at transplanting or early seasondiminishes (Liu and Meister, 2001; Polumboet al., 2001).

Extensive reliance on chemical insecti-cides for whitefly control has resulted inwhitefly resistance to almost all major classesof conventional insecticides throughout theworld (Omer et al., 1992; Polumbo et al.,2001; Wardlow et al., 1972, 1975, 1976; Zouand Zheng, 1988). We recently detectedsignificant tolerance/resistance of the green-house whitefly to imidacloprid in strawberryin California (Bi and Toscano, 2007). Ourresults strongly emphasize the need todevelop resistance management strategies inthe region. Introduction of novel insecticideswith distinct modes of action into the currentwhitefly control program is a valuable tacticfor resistance management (Denholm et al.,2002; Liu, 2004).

Spiromesifen is a novel insecticide andacaricide belonging to the new chemical classof spirocyclic phenyl-substituted tetronicacids (Nauen et al., 2002). This compoundacts on interfering with insect/mite lipid bio-synthesis (Nauen et al., 2002). Spiromesifenis especially active against whiteflies (Bemi-sia spp. and Trialeurodes spp.) and spidermites (Tetranychus spp.) in several croppingsystems, including cotton (Gossypium hirsu-tum L.), vegetables, and ornamentals (Liu,2004; Nauen et al., 2002; Polumbo, 2004).The present study was initiated to test theefficacy of spiromesifen against the green-house whitefly on strawberry under bothlaboratory and field conditions.

Materials and Methods

Laboratory experimentPlants, insects, and insecticides. Straw-

berry bare-root seedlings (cv. Camarosa fromSierra-Cascade Nursery, Susanville, Calif.)were planted in 2.6-L pots filled with a 1.3:1sand: peatmoss mixture (by volume) in envi-ronmental growth chambers. Plants used inthe experiments were at the three to fivetrifoliate stage. Plants were watered every2 d. At the time of planting, 5 g of Osmocotefertilizer (14N–14P–14K) was applied toeach pot. The environmental growth cham-bers were set at 23 �C during the day and18 �C at night, 60% relative humidity, with a12:12-h photoperiod provided by fluorescentand incandescent lamps (ratio of irradi-ance between fluorescent and incandescentlamps = 4:1).

Adult greenhouse whiteflies were col-lected from commercial strawberry fields insouthern California (Oxnard, VenturaCounty) in 2004 and were immediately usedfor bioassay experiments. Immature green-house whiteflies used in the experiment weredeveloped from eggs laid by the field-col-lected whitefly adults. Spiromesifen (Oberon2SC) was obtained from Bayer CropScience,Research Triangle Park, N.C. The insecticidewas diluted in deionized water. Nonionicwetter/spreader (Kinetic-1, from Bayer

Received for publication 3 Oct. 2006. Accepted forpublication 13 Nov. 2006.We thank H.C. ‘‘Skip’’ Larson of Sierra-CascadeNursery, Inc., for providing strawberry seedlingsin this study and G.R. Ballmer and X.F. Li forassistance.This research was funded by the California Straw-berry Commission and Bayer CropScience.1To whom reprint request should be addressed;e-mail jianbi@citrus.ucr.edu.

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CropScience) was added to the insecticidesolution at a concentration of 0.1% (v/v).

Bioassay. Leaflets of strawberry plantswere sprayed until runoff, ensuring completecoverage of both upper and lower surfaceswith a specific amount of the insecticidedissolved in deionized water containingKinetic-1. Control plants were sprayed withkinetic water solution only. Three to fiveplants were used for each treatment rate andthe control. After the leaf surface was dried, 30greenhouse whitefly adults were clip-caged onthe lower side of a leaflet of the most recentlyfully expanded trifoliate (cage size 4 cm2 indiameter and 2 cm in depth). Adults wereaspirated into pipette tips and gently releasedinto the cages. Adult mortality was determinedat 72 h after initial exposure.

For egg and immature greenhouse white-fly bioassay, 40 adults were clip-caged on thelower side of a leaflet of the most recentlyfully expanded trifoliate. After an ovipositionperiod of 24 h, the adults were removed. Theinfested plants were sprayed as describedpreviously with the insecticide solution wheneggs (1 d old), first instar (10 d old), secondinstar (14 d old), and third instar (24 d old)nymphs were present. Egg mortality wasdetermined at 11 d posttreatment, whereasnymph mortality was determined at 14 d post-treatment when they failed to develop intotheir next stages (instars).

Field experimentExperimental plots. The strawberry bare-

root seedlings (cv. Camarosa) were planted inthe Fall of 2003 on four-row beds in acommercial strawberry field in southernCalifornia (Bonsall, San Diego County).Each bed was 1.3-m wide and 50-m long.The test was arranged in a randomized com-plete block design with five replicates. Plotsize was 3-m long · 1.3-m wide with a 1-mbuffering area between the plots. There were�40 plants in each plot.

I n s e c t i c i d e c o n c e n t r a t i o n s a n dapplications. Efficacy of spiromesifenagainst the greenhouse whitefly was evalu-ated using applications of buprofezin andpyriproxyfen as comparisons. Buprofezin(Applaud 70 WP) was obtained from AgrEvoUSA Company, Pikeville, N.C., whereaspyriproxyfen (Esteem 0.86 EC) was obtainedfrom Valent USA Corporation, WalnutCreek, Calif.

Insecticides applied at the label-recom-mended concentrations were as follows: spi-romesifen at 283.8 g�ha–1 a.i., buprofezin at388.8 g�ha–1 a.i., and pyriproxyfen at 60.0g�ha–1 a.i. All the insecticides were applied on29 Mar. 2004 at a volume of 946 L of waterper hectare with an ECHO air-assistedsprayer. Control plots were left untreated.

Whitefly sampling methods. Sampling ofwhitefly adults, immatures, and eggs wasinitiated 1 week after application of all theinsecticides on a weekly basis and ended inmid-May. The 10 youngest and fullyexpanded middle leaflets of trifoliates, eachfrom a randomly selected plant in each of theplots, and 10 older leaflets from the same

Fig. 1. Effect of spiromesifen treatment on (A) egg hatching rate and mortality of (B) first instar, (C)second instar, (D) third instar, and (E) adult greenhouse whiteflies on strawberry. Error bars representstandard errors.

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plants in each plot were excised. These leaf-lets were placed into plastic zip-lock bags andtransported in a cooler to the laboratory tocount eggs (on young leaflets) and immatures(on older leaflets) using a stereo dissectingmicroscope. Adult whiteflies were collectedwith an engine-powered vacuum (Allen-Vac)(Osborne and Allen, 1999; Bi et al., 2001)over the top of one of the center two rows,either the second or third row (alternatedbetween the center rows in different samplingdates) in each plot. The collected sampleswere transported to the laboratory and thenumbers of adults were counted under amicroscope. Numbers of other insect pests inthe samples were negligible and not counted.

Statistical analyses. Least significant dif-ference test in one-way randomized completeblock design of analysis of variance in SAS(SAS Institute, 2001) was used in the fieldexperiment to analyze the data and separatethe means for samples from each samplingdate. Before the analysis of variance, num-bers of whitefly adults, immatures, and eggswere transformed using the formula log (y + 1)to normalize the data.

Results

Laboratory experiment. Egg stage of thegreenhouse whitefly was very susceptible tospiromesifen (Fig. 1A). Egg hatching wasinhibited nearly 80% at a spiromesifen con-centration of 0.5 mg�mL–1 a.i., whereas com-plete inhibition of egg hatching occurred at aconcentration of 1.0 mg�mL–1 a.i., a 300-foldlower than the label recommended rate(300 mg�mL–1 a.i.).

Spiromesifen was highly toxic to imma-ture greenhouse whiteflies (Fig. 1B–D). At aconcentration of 1.6 mg�mL–1 a.i., spiromesi-fen caused 91% mortality of the first instarnymphs; and at a concentration of 3.1mg�mL–1 a.i., near 100-fold lower than thelabel recommended rate, it killed 100% ofthe nymphs (Fig. 1B). At a concentration of3.0 mg�mL–1 a.i. (100-fold lower than the labelrecommended rate), this compound killed thesecond instars completely (Fig. 1C); and at aconcentration of 10.0 mg�mL–1 a.i. (30-foldlower than the label recommended rate), itkilled 100% of the third instars (Fig. 1D).

Spiromesifen was moderately toxic toadult greenhouse whiteflies (Fig. 1E). Atconcentrations of 50.0, 100.0, and 200.0mg�mL–1 a.i., it killed 65%, 61%, and 65%of the adults, respectively (Fig. 1E).

Field experiment. Application of spiro-mesifen decreased egg numbers by 55% to73% (P < 0.05) from 2 (12 Apr.) to 5 weeks(3 May) posttreatment, compared with theuntreated control, after which the egg num-bers were similar (P > 0.05) in the treated andthe control plots (Fig. 2A). Spiromesifentreatment reduced egg numbers by 61% to80% (P < 0.05) from 2 (12 Apr.) to 3 weeks(19 Apr.) posttreatment in comparison withthe pyriproxyfen treatment, after which thenumbers were similar (P > 0.05) between thetwo treatments (Fig. 2A). Compared withthe buprofezin treatment, spiromesifen appli-

cation lowered the egg numbers by 34% to73% (P < 0.05) from 2 (12 Apr.) to 5 weeksposttreatment (Fig. 2A).

When compared with the untreated con-trol, spiromesifen treatment depressed thenumbers of immatures by 45% and 49%(P < 0.05), respectively, at 1 (5 Apr.) and2 weeks (12 Apr.) posttreatment, whereasthe numbers were decreased by 79% to 95%(P < 0.05) from 3 (19 Apr.) to 7 weeks (17May) posttreatment (Fig. 2B). In comparisonwith pyriproxyfen treatment, spiromesifenapplication reduced the immature numbersby 29% at 1 week posttreatment and by 52%to 92% (P < 0.05) from 2 to 6 weeks posttreat-ment (Fig. 2B). Compared with buprofezintreatment, the effect of spiromesifen on reduc-tion of immature numbers was similar (P >0.05) on all the sampling dates except 12 Apr.,

when the immature numbers were 3.2-foldgreater (P < 0.05), and 10 May, when thenumbers were 79% fewer (P < 0.05) (Fig. 2B).

Adult whitefly numbers started to besignificantly decreased (P < 0.05) from2 weeks posttreatment (12 Apr.) and theefficacy lasted for another 3 weeks (until 3May) in spiromesifen treatment comparedwith the untreated control (Fig. 2C). Thedecrease in adult numbers ranged from 49%to 62%. The adult numbers in spiromesifenand pyriproxyfen treatments were similar(P > 0.05) on all sampling dates. Differencesin adult numbers between spiromesifen andbuprofezin treatments were also not signifi-cant (P > 0.05) on all sampling dates except26 Apr., when the number was 42% greater(P < 0.05) in the buprofezin treatment than inthe spiromesifen treatment (Fig. 2C).

Fig. 2. Efficacy of spiromesifen, pyriproxyfen and buprofezin treatments on numbers of (A) eggs,(B) immatures, and (C) adults of greenhouse whitefly on strawberry. Error bars represent standarderrors.

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Discussion

Our laboratory test revealed that spirome-sifen was very effective in inhibiting thewhitefly egg hatching, highly toxic to theimmature whiteflies, and moderately effectivein killing the adult whiteflies on strawberry(Fig. 1A–E). Nauen et al. (2002) reported thatspiromesifen was especially active against thegreenhouse whitefly, particularly in the juve-nile stages on cotton. Liu (2004) showedspiromesifen was highly toxic to nymphsand slightly toxic to adults of silver-leafwhitefly (B. tabaci Gennadius) on both mel-ons and collards (Brassica oleracea L.). How-ever, Liu’s results indicated that spiromesifenwas nontoxic to B. tabaci eggs (Liu, 2004).The difference in inhibition of egg hatching ofthe greenhouse whitefly and the silver-leafwhitefly may be the result of the differences inwhitefly species or host plant species.

Pyriproxyfen is an insect growth regulatoraffecting the hormonal balance in insects,whereas buprofezin is another insect growthregulator inhibiting chitin synthesis in insects(De Cock et al., 1990; Ishaaya and Horowitz,1998). We previously conducted both green-house and field experiments to evaluate pyr-iproxyfen and buprofezin against thegreenhouse whitefly on strawberry in southernCalifornia (Bi et al., 2002a, 2002b). In thegreenhouse experiment, we showed that pyr-iproxifen was excellent in inhibition of egghatching of the whiteflies, whereas buprofezinis highly effective against growth and devel-opment of the immatures (Bi et al., 2002a,2002b). In the field experiment, we demon-strated that both pyriproxyfen and buprofezinsignificantly suppressed the whitefly popula-tions on both fall- and summer-planted straw-berry (Bi et al., 2002a, 2002b). As a result ofthe excellence in controlling their targetinsects, low toxicity to mammals, and relativesafety to most parasitoids, buprofezin andpyriproxifen are considered as important com-ponents of integrated greenhouse whiteflymanagement programs. In this study, ourlaboratory experiment showed that spiromesi-fen was highly effective against both eggs andthe immatures of the greenhouse whitefly andmoderately effective against the adults (Fig.1A–E). Our field experiment clearly indicatedthat spiromesifen was superior to pyriproxy-fen in reducing the whitefly egg and immaturenumbers (Fig. 2A, B). Spiromesifen was alsosuperior to buprofezinin in decreasing thewhitefly egg numbers (Fig. 2A). The effectof spiromesifen on reduction of the immaturenumbers was similar to that of buprofezin(Fig. 2B).

It was reported that spiromesifen is safeon beneficial organisms and has a favorableenvironmental profile (Nauen et al., 2002).Spiromesifen is also extremely effectiveagainst pyriproxyfen-resistant whiteflies andno crossresistance to any important insecti-cide and acaricide was found (Nauen et al.,2002). Together with results in this study, weconclude that spiromesifen can be a newcomponent of the integrated greenhousewhitefly management programs on straw-berry and can be a new valuable tool in thewhitefly resistance management programs.

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