Effect of cyantraniliprole on feeding behavior and virus transmission of Frankliniella fusca and Frankliniella occidentalis (Thysanoptera: Thripidae) on Capsicum annuum

Crop Protection 54 (2013) 251e258

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Effect of cyantraniliprole on feeding behavior and virus transmission of Frankliniella fusca and Frankliniella occidentalis (Thysanoptera: Thripidae) on Capsicum annuum Alana L. Jacobson*, George G. Kennedy** Department of Entomology, North Carolina State University, Box 7630, 3210 Ligon Street, Raleigh, NC 27695-7630, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 7 May 2013 Received in revised form 20 August 2013 Accepted 28 August 2013

The anthranilic diamide insecticide cyantraniliprole was previously shown to reduce transmission of Tomato spotted wilt virus (TSWV) to pepper, Capsicum annuum, by Frankliniella fusca but not Frankliniella occidentalis. This study examines the effects of cyantraniliprole and imidacloprid on thrips feeding using electrical penetration graphing (EPG), and on TSWV transmission in field cage studies. Some antifeedant responses were observed in the EPG studies when thrips fed on cyantraniliprole- and imidaclopridtreated plants; however, these responses were variable between species and among the 2, 6, and 10 day post-treatment time intervals during which feeding behavior was observed. Cyantraniliprole significantly reduced the probability of TSWV infection when spread by F. fusca in field-grown pepper when viruliferous thrips were released 7 days but not when released at 14 days after the insecticide treatment in one of 2 field trials. In the second trial cyantraniliprole significantly reduced the probability of infection when F. fusca were released 14 days but not 7 days after treatment. In both years, imidacloprid prevented or significantly reduced transmission of TSWV by F. fusca in field-grown pepper when viruliferous thrips were released 7 days and 14 after treatment. In one of two years, cyantraniliprole significantly reduced the incidence of TSWV in field-grown pepper that was spread by F. occidentalis when viruliferous thrips were released 7 days after the insecticide treatment, but not 14 days after the treatment. Imidacloprid did not reduce the incidence of TSWV in field-grown pepper when viruliferous F. occidentalis were released. Although these studies demonstrate that probing behavior of these thrips species is altered on cyantraniliprole-treated pepper plants, results of field cage studies did not consistently show a reduction in incidence of TSWV-infected plants. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Tomato spotted wilt virus Imidacloprid Cyazypyr Anthranilic diamide Frankliniella spp. Electrical penetration graph

1. Introduction Tomato spotted wilt virus (TSWV), a devastating tospovirus of worldwide importance, is a major problem affecting tobacco, peanut, pepper, tomato, potato, and ornamental crops in the U.S. (Pappu et al., 2009). Although TSWV is persistently transmitted by at least nine species of thrips (Riley et al., 2011), Frankliniella occidentalis Pergande and Frankliniella fusca Hinds are the two primary vector species implicated in TSWV epidemics in the U.S. (Culbreath et al., 2003; Groves et al., 2001a,b; McPherson et al., 1999; Reitz et al., 2003; Riley and Pappu, 2000, 2004; Salguero et al., 1991). Because TSWV transmission can occur during thrips feeding bouts

* Corresponding author. Tel.: þ1 919 515 1657; fax: þ1 919 515 3748. ** Corresponding author. Tel.: þ1 919 515 1657; fax: þ1 919 515 3748. E-mail addresses: [email protected] (A.L. Jacobson), george_kennedy@ ncsu.edu (G.G. Kennedy). 0261-2194/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cropro.2013.08.018

of 5e10 min (Wijkamp et al., 1996), management of thripstransmitted tospoviruses has proven difficult. Management typically involves integrated approaches that aim to increase plant resistance, reduce attractiveness of susceptible crop hosts to dispersing thrips, and deter thrips feeding on host plants. A variety of techniques have been shown to reduce TSWV transmission, including properly timed chemical applications, reflective mulches, and resistant varieties; however, with the exception of single major alleles conferring resistance to TSWV in tomato and pepper, which can be overcome by resistance-breaking strains of TSWV, no single method can be relied on to provide adequate control of TSWV (Aramburu and Martí, 2003; Chatzivassiliou, 2008; Csinos et al., 2001; Culbreath et al., 2003; Diaz-Montano et al., 2010; Greenough et al., 1990; Mandal et al., 2008; Moury et al., 1997; Riley and Pappu, 2004). Management of TSWV is further complicated because methods vary in effectiveness and availability depending on the vector species and cropping system (Chatzivassiliou, 2008; Csinos et al., 2001; Herbert et al., 2007; Riley and Pappu, 2004).

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Chemical tools for managing tospoviruses in crops are very limited. The only materials currently available either increase plant defenses (phorate, acibenzolar-S-methyl) or alter the feeding behavior of the thrips vectors (imidacloprid). These chemistries, however, are not equally effective in all crop plants or against all vectors, and are only effective if their applications are timed properly, before movement of viruliferous thrips into the crop field occurs (Chatzivassiliou, 2008; Csinos et al., 2001; Groves et al., 2001b; Herbert et al., 2007; Joost and Riley, 2005; Mandal et al., 2008; Pappu et al., 2000; Riley and Pappu, 2004). New chemistries that can be rotated with existing chemistries to delay development of resistance, or that are effective against a broader range of vectors would be a valuable addition to existing management tools. Cyantraniliprole belongs to the anthranilic diamide class of insecticides that target ryanodine receptors in insect muscle cells, and whose chemistries exhibit varying degrees of antifeedant activities in different groups of insects (GonzalesColoma et al., 1999; Cordova et al., 2006; IRAC, 2012; Lahm et al., 2005, 2007; Sattelle et al., 2008). Cyantraniliprole is reported to be active against sucking insects, including some that vector plant viruses (Burt and Karr, 2008; Sattelle et al., 2008). Treatments of cyantraniliprole have been shown to decrease the proportion of plants infected with viruses that are persistently transmitted by whiteflies in field trials (Castle et al., 2009), reduce feeding by whitefly nymphs, and cause mortality of nymphs that fed on treated plants (Cameron et al., 2013). In a previous greenhouse study with pepper (Capsicum annuum L), drench applications of cyantraniliprole applied at a rate of 4.41 mg a.i. per plant, were shown to reduce transmission of TSWV by F. fusca but not F. occidentalis. Antifeedant effects were thought to be responsible for the decrease in virus transmission by F. fusca because a higher level of thrips mortality was not observed on treated plants (Jacobson and Kennedy, 2011). While these studies highlight the potential of cyantraniliprole to decrease incidence of thripstransmitted plant virus diseases such as TSWV, further studies were needed to test this chemistry under field conditions and to determine if cyantraniliprole has antifeedant effects on F. fusca and F. occidentalis. Electrical penetration graph (EPG) methods have been used to examine feeding behaviors of piercing-sucking insects in response to host-plant traits and insecticide treatments (Butler et al., 2012; Lei et al., 2001). The EPG procedure incorporates an insect and a feeding substrate into an electrical circuit that is completed when the insect inserts its stylets into the feeding substrate. Once the circuit is complete, resistance and voltage fluctuations create distinct waveforms that correspond to probing, salivation, and ingestion events and can be recorded (Walker, 2000). EPG studies of the effects of imidacloprid treatments on the feeding behavior of F. fusca and F. occidentalis showed a decrease in probing and feeding by F. fusca in response to this treatment, and an increase in probing by F. occidentalis (Groves et al., 2001a; Joost and Riley, 2005). These results provided an explanation for why imidacloprid treatments reduce virus transmission by F. fusca, but not F. occidentalis. EPGs were used in this study to investigate potential antifeedant effects of cyantraniliprole on the feeding behavior of F. fusca and F. occidentalis. This study was undertaken to expand on the previous finding of Jacobson and Kennedy (2011) that a soil-drench treatment of cyantraniliprole reduced transmission of TSWV to C. annuum by F. fusca but not F. occidentalis under laboratory conditions in the absence of an increase in thrips mortality. Herein, we present results from EPG studies demonstrating effects of cyantraniliprole on probing behavior of F. fusca and F. occidentalis, and results from small-plot field trials comparing effects of water, cyantraniliprole, and imidacloprid treatments on transmission of TSWV to

C. annuum by F. fusca and F. occidentalis. Imidacloprid was included in these experiments because it has been demonstrated to reduce feeding and TSWV transmission by F. fusca but not F. occidentalis (Groves et al., 2001b; Joost and Riley, 2005). 2. Materials and methods 2.1. EPG experiments Adult F. fusca and F. occidentalis were obtained from laboratory colonies maintained separately on Phaseolus vulgaris L. bean pods in controlled environments at 24  C with ca. 60% RH and a photoperiod of 14:10. Banana pepper (C. annuum L.) seeds were germinated in an insect-free greenhouse. Plants at the four-true-leaf stage were transplanted to individual 296 ml plastic cups (Solo Cup Company, Lake Forest, IL, USA) with a 25 mm diameter, round, fine mesh screen on the bottom. After transplanting, each plant received a soil-drench application of 50 ml of either distilled water, 10 mg a.i./ plant of cyantraniliprole (CyazypyrÔ 200 SC; DuPont, Delaware, USA), or 13.2 mg a.i./plant of imidacloprid (AdmireÒ Pro; Bayer, Kansas City, MO, USA). Both insecticides were applied at the current (imidicloprid) or anticipated (cyantraniliprole) labeled rate for drench applications to control thrips on pepper. Plants were then held at room temperature, under grow lights, and in insect-proof cages until they were used in EPG experiments at 2, 6 or 10 days post-treatment. To prepare thrips for EPG recording, two or three day-old, adult female thrips were tethered to a 2 cm long, 0.12 mm diameter, gold wire (EPG Systems, Wageningen, The Netherlands) with silver paint (Pelco colloidal silver liquid, Ted Pella, Inc., Redding, CA, USA). Thrips were fasted for 30 min after being attached to the wire before starting the EPG. Treated plants were placed into Faraday cages and the thrips placed onto the adaxial surface of the youngest fully expanded leaf for the EPG recording, which lasted for 4 h under ambient laboratory conditions. One Giga-4 DC-EPG system and one Giga-8 DC EPG system (EPG Systems, Wageningen, The Netherlands) with 1 GU of input resistance were used to record EPGs. Separate EPG experiments were conducted for F. fusca and F. occidentalis. A randomized design was used for these experiments: the effect of the three treatments was examined 2, 6, and 10 days after treatment (DAT) for each thrips species. EPGs were recorded and waveforms labeled using Stylet þ Software (EPG Systems, Wageningen, The Netherlands) and according to the feeding waveforms previously described for F. occidentalis (Kindt et al., 2003, 2006). SAS Software (SAS Institute, Cary, NC, USA) was used to calculate and analyze sequential and non-sequential EPG feeding waveforms according to Backus et al. (2007) and Sarria et al. (2009). We hypothesized that if cyantraniliprole exhibits antifeedant properties against these two thrips species then the number of probing/feeding events and the amount of time spent feeding on a treated plant should be decreased. In addition, we reasoned that a strong antifeedant response may be observed in early probes, given that an almost immediate antifeedant response has been reported with another anthranilic diamide, chlorantraniliprole, against Lepidopteran larvae (Hannig et al., 2009). Therefore, the EPG variables we report are those we deemed most relevant to our objective of investigating antifeedant effects of cyantraniliprole on F. fusca and F. occidentalis: the total amount of time spent probing/feeding on the plant, the total number of probes, duration of 1st and 2nd probes, and the number and duration of abnormal feeding waveforms. In this paper, thrips abnormal feeding indicates the observation of feeding waveforms not previously described in the literature. It is possible that some of the waveforms we report as abnormal include the previously

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described waveform X (Kindt et al., 2003, 2004); however, the abnormal waveforms we observed appeared most commonly in insects fed on plants treated with insecticides, typically occurred during long probes, and did not conform to the description given for X waveforms. Data on numbers of events (e.g. number of probes) were transformed to square root (x þ 0.1) and data on duration of events were transformed to natural log (x þ 1) prior to analysis. The Proc GLIMMIX procedure of SAS 9.3 (SAS Institute, Cary, NC) with mean separation by LS Means was used to determine significant differences among treatments. Two analyses were conducted. In the first, data were analyzed to examine the significance of treatment effects averaged over all post-treatment times (2, 6, and 10 days post treatment). In this analysis, treatment was treated as a fixed effect and date, individual insect, and post-treatment times were treated as random effects because these all represent independent observations (repeated measures were not taken on the plants). In the second analysis, data for the 2, 6, and 10 day post-treatment times were analyzed separately to examine the effect of treatments on EPG parameters at each post-treatment time. 2.2. Small plot field trials The effects of transplant water applications of cyantraniliprole on transmission of TSWV to banana pepper (C. annuum) by F. fusca and F. occidentalis were compared to those of imidacloprid and a water control in experiments that entailed releasing putatively viruliferous thrips into field cages at 7 and 14 days after application of the chemical treatments. Because virus acquisition by thrips and subsequent transmission to pepper plants can be affected by uncontrollable environmental conditions, each species by posttreatment release time combination was examined in a separate experiment and each experiment was repeated in 2011 and 2012. Individual plots within each experiment were caged as described below and consisted of 10 pepper plants spaced 12 cm apart. Plots were separated within rows by 1 m and across rows by 1.22 m. Transplants, approximately 6 weeks old, were hand set in holes to which 100 ml of the transplant water treatment was added before the soil was closed around the transplant. The experimental chemical treatments consisted of cyantraniliprole (CyazypyrÔ 200 SC) at 10 mg a.i. per plant or imidacloprid (AdmireÒPro) at 11.8 mg a.i./plant, respectively, applied in the transplant water. These represent the anticipated label rate for cyantraniliprole and the current label rate for imidacloprid on pepper. The untreated control plots received only water. All plants within a plot received the same treatment and each 10-plant plot was caged immediately after transplanting. Cages consisted of arches constructed from flexible, black plastic tubing (61 cm wide at the base and 61 cm high at the apex of the arch) anchored by rebar and covered by agricultural row-cover (Agribon þ AG-30; PGI Nonwovens, Inc., Ponchatoula, LA). The row cover was secured by sod staples. Plots were irrigated as necessary using overhead sprinklers. Each experiment was conducted as a randomized complete block design. The 2011 experiments were replicated 4 times with blocks arranged perpendicular to a shade gradient resulting from the presence of trees on the east side of the experimental site. In these experiments the transplants were set and treatments applied on August 21. A similar planting arrangement was used in the 2012 experiments except that each treatment included 2 planting dates to ensure that sufficient numbers of thrips would be available for release at the appropriate times after transplant. Each treatment was replicated 6 times in a randomized complete block design with blocks arranged perpendicular to a shade gradient. All treatment by planting date combinations appeared once within each block and were randomized within each treatment. The planting dates were

253

Table 1 Mean EPG feeding parameters recorded over a 4 h period for Frankliniella fusca and F. occidentalis that fed on water-, cyantraniliprole-, and imidacloprid-treated Capsicum annuum averaged over the three post-treatment intervals. Feeding behavior Frankliniella fusca Total number probes Total timec probing Durationc of 1st probe Duration of 2nd probe Number of abnormal waveforms Total duration of abnormal waveforms Frankliniella occidentalis Total number probes Total time probing Duration of 1st probe Duration of 2nd probe Number of abnormal waveforms Total duration of abnormal waveforms

Water Nb Cyantraniliprole N

Imidacloprid N

107aa 5584a 9.9a 5.1a 0.16b

27c 125c 3.6b 2.4b 0.37b

47 ab

121a 1154a 4.0a 3.2a 0.1b 33a

44 44 44 44 8

54b 2949b 3.8b 3.4 ab 1.5a

8 182a

42 42 42 42 3

83a 803 ab 5.0a 4.2a 0.3a

3 38a

53 53 53 53 32

61 61 61 61 16

32 23b

16

39 39 39 39 12

44 44 44 44 8

39b 566b 3.8a 4.3a 0.2 ab

12 83a

8

a Values are back-transformed LS means. Data on number of occurrences transformed to square root (x þ 0.1) and data on duration of events transformed to natural log (x þ 1) prior to analysis. Mean separation horizontal across treatments for each EPG variable; treatment LS Means at P  0.05. b N is the total number of recordings that included the feeding behavior analyzed. c Total time and duration variables are given in seconds.

April 24 and May 8 in the F. occidentalis experiments and May 15 and May 29 in the F. fusca experiments. The TSWV isolate used was collected from pepper in Montgomery County, NC in May 2011. The F. fusca and F. occidentalis were obtained from the laboratory colonies described previously. Viruliferous adult females for release into the caged plots were obtained by confining cohorts of neonates on excised Emilia sonchifolia L. foliage infected with TSWV. Following an acquisition access period of 48 h, they were reared to adult on non-infected pole bean (P. vulgaris) pods at 85  F, 40% RH, 14:10 L:D. The resulting potentially viruliferous F. fusca and F. occidentalis were released into their respective plots 7 or 14 days after treatments. In each plot scheduled for release of viruliferous thrips, one microcentrifuge tube (Fischer Scientific, Rochester, NY) containing ten, 2 to 4 day-old adult male and female thrips was placed at the base of each plant in each experimental plot and opened to release the thrips. To confirm the infectious status of the thrips released into the field plots, adults from the same cohort of thrips released in the field were tested for transmission of TSWV to E. sonchifolia in the laboratory. Five adults per plant were released on to individually caged E. sonchifolia seedlings where they remained confined for three weeks. The plants were then visually scored for TSWV infection based on symptoms. Following release of the thrips, plots were checked weekly for four weeks and plants expressing symptoms of Tomato spotted wilt virus (TSWV) infection were tagged and counted. One to three weeks after the thrips were released the youngest, fully expanded leaf was sampled from each visually symptomatic plant, and subjected to DAS-ELISA using a commercially available kit (Agdia, Inc., Elkhart, IN) to confirm infection. Four weeks after thrips were released, all plants not previously confirmed to be infected were tested using DAS-ELISA to identify any asymptomatic infections. Final plant stand counts were taken during the week-four sample. No plants died from TSWV infection during the experiment. Data were analyzed using logistic regression (Proc Logistic in SAS 9.3). The statistical analysis initially modeled the likelihood that a plant became infected with TSWV as a function of block and the chemical treatment in 2011 and block, planting date and

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Fig. 1. A represents normal probing waveforms produced by both F. fusca and F. occidentalis; B & C represent variations in the previously undescribed waveforms produced more frequently by thrips feeding on cyantraniliprole-treated plants.

chemical treatment in 2012. Block effects were not significant in any analysis (P > 0.680 in all cases) and block was removed from the model prior to subsequent analysis of treatment effects using type III tests. In 2012 planting date also was not significant and was removed from the model prior to subsequent analysis of treatment effects using type III tests for significance of odds ratios for each chemical treatment and the water-treated control. Contrasts were used to test for significance of the odds ratios for the two chemical treatments. Because no infections were observed in the 7-day release experiment in 2011 and in the 7- and 14-day release experiments in 2012, differences between odds ratios involving the imidacloprid treatment could not be estimated and results are presented only for the cyantraniliprole vs water contrasts in these experiments. 3. Results 3.1. EPG experiments The effects of treatment on probing by F. fusca over the 10-day period following treatment application (Table 1) were significant for total number of probes, total time probing, duration of 1st probe, duration of 2nd probe, number of abnormal waveforms, and total duration of abnormal waveforms. Both cyantraniliprole and imidacloprid significantly reduced the total number of probes (P < 0.0001, t127 ¼ 5.60; P < 0.0001, t127 ¼ 10.12; respectively), the total time spent probing (P ¼ 0.0092, t127 ¼ 2.65; P < 0.0001, t127 ¼ 16.24; respectively), and the duration of the 1st probe (P ¼ 0.0086, t127 ¼ 2.67; P ¼ 0.0041, t127 ¼ 2.92; respectively) relative to the water-treated control plants, and imidacloprid caused significantly greater reductions in the total number of probes (P < 0.0001, t127 ¼ 4.57) and the total time spent probing (P < 0.0001, t127 ¼ 14.16) than cyantraniliprole. Imidacloprid also significantly reduced the duration of the 2nd probe compared to water (P ¼ 0.0200, t127 ¼ 2.36), but not cyantraniliprole

(P ¼ 0.2939, t127 ¼ 1.05). The 50% reduction in total number of probes caused by cyantraniliprole, although large, was less than the 75% reduction observed on imidacloprid-treated plants. Similarly, the 47% reduction in total time spent probing on cyantraniliproletreated plants was dramatically less than the 98% reduction observed on imidacloprid-treated plants. The reduction in number and duration of probes by F. fusca on imidacloprid-treated plants agrees with previous reports of this response by Groves et al. (2001a). The number of abnormal waveforms (Fig. 1) produced was significantly greater on cyantraniliprole-treated than on waterand imidacloprid-treated plants (P < 0.0001, t127 ¼ 4.25; P ¼ 0.0005, t127 ¼ 3.55; respectively). The total duration of abnormal waveforms produced during probing was also significantly greater on cyantraniliprole-treated than imidaclopridtreated plants (P ¼ 0.0005, t30 ¼ 3.89). However, neither the cyantraniliprole nor the imidacloprid treatments differed significantly from the water-treated control in total duration of abnormal waveforms (P ¼ 0.0594, t30 ¼ 1.96; P ¼ 0.3633, t30 ¼ 0.92; respectively). When the data were analyzed by post-treatment time interval (Table 2) the effect of treatment on mean number of probes by F. fusca was significant at 2, 6 and 10 days after treatment. At 2, 6, and 10 days after treatment there were significantly fewer probes on cyantraniliprole- (P ¼ 0.0115, t32 ¼ 2.68; P < 0.0001, t49 ¼ 4.36; P ¼ 0.0147, t40 ¼ 2.55, respectively) and imidacloprid-treated plants (P ¼ 0.0009, t32 ¼ 3.64; P < 0.0001, t49 ¼ 7.69; P < 0.0001, t40 ¼ 6.26; respectively) compared to the water-treated control. At 6 and 10 days after treatment there were significantly fewer probes on imidacloprid- than on cyantraniliprole-treated plants (P ¼ 0.0019, t49 ¼ 3.27; P ¼ 0.0007, t40 ¼ 3.67; respectively), but these treatments were not significantly different from each other 2 days after treatment (P ¼ 0.3081, t32 ¼ 1.04). The effect of treatment on total time spent probing by F. fusca was significant in recordings made at 2, 6 and 10 days after treatment. The total time F. fusca spent probing on cyantraniliprole-

A.L. Jacobson, G.G. Kennedy / Crop Protection 54 (2013) 251e258 Table 2 Mean EPG feeding parameters recorded over a 4 h period for Frankliniella fusca and F. occidentalis that fed on water-, cyantraniliprole-, and imidacloprid-treated Capsicum annuum at 2, 6 and 10 days after treatment. Feeding behavior Frankliniella fusca Number probes

Treatment

Water Cyantraniliprole Imidacloprid d Total time probing Water Cyantraniliprole Imidacloprid Durationd of 1st Water probe Cyantraniliprole Imidacloprid Duration of 2nd Water probe Cyantraniliprole Imidacloprid Number abnormal Water events Cyantraniliprole Imidacloprid Duration abnormal Water feeding Cyantraniliprole Imidacloprid Frankliniella occidentalis Number probes Water Cyantraniliprole Imidacloprid Total time probing Water Cyantraniliprole Imidacloprid Duration of 1st Water probe Cyantraniliprole Imidacloprid Duration of 2nd Water probe Cyantraniliprole Imidacloprid Number abnormal Water events Cyantraniliprole Imidacloprid Duration abnormal Water feeding Cyantraniliprole Imidacloprid

2 DATa

Nb

6 DAT

N

10 DAT

N

104ca 48b 35b 519a 480a 383b 5.4a 2.6a 6.2a 5.5a 2.1a 3.9a 0.01a 0.9a 0.7a 8.6a 14.1a 51a

9 15 20 9 15 20 9 15 20 9 15 20 1 8 6 1 8 6

105a 50b 23c 5406a 2268b 76c 20.5a 3.5b 2.6b 7.0a 4.7 ab 2.0b 0.3b 1.9a 0.2b 68 ab 146a 8.4b

18 21 23 18 21 23 18 21 23 18 21 23 5 11 5 5 11 5

113a 67b 22c 4199a 2277a 74b 5.2a 5.5a 3.2a 3.6a 3.4a 2.2a 0.1b 1.9a 0.5b 38a 719a 84a

17 17 18 17 17 18 17 17 18 17 17 18 2 13 5 2 13 5

65a 82a 48a 846a 853a 648a 4.6a 5.1a 3.7a 2.2a 2.2a 3.9a 0b 0.1 ab 0.3a NAe 34a 98a

12 8 18 12 8 18 12 8 18 12 8 18 0 3 5 0 3 5

183a 47b 24b 1825a 628b 390b 7.0a 4.6a 3.7a 7.6a 7.1a 2.8a 0.1a 0.6a 0.2a 15a 56a 58a

11 11 8 11 11 8 11 11 8 11 11 8 1 5 2 1 5 2

146a 114a 40b 1129a 937 ab 608b 2.8a 5.4a 4.2a 2.4a 4.2a 4.9a 0.1a 0.3a 0.04a 30f 24f 124f

19 20 18 19 20 18 19 20 18 19 20 18 2 4 1 2 4 1

a DAT is the post-treatment time interval that the EPG recordings were obtained in days after treatment. b N is the total number of recordings that included the feeding behavior analyzed. c Values are back-transformed LS means. Mean separations among treatments for each feeding parameter during each post-treatment time interval were performed by treatment LS Means at P  0.05. Data on number of occurrences transformed to square root (x þ 0.1) and data on duration of events transformed to natural log (x þ 1) prior to analysis. d Total time and duration variables are given in seconds. e NA ¼ LS Mean value not available due to too few observations. f Mean separation not available.

treated plants was significantly less than on water-treated plants at 6 (P ¼ 0.0096, t49 ¼ 2.70) but not at 2 or 10 days post-treatment (P ¼ 0.9107, t32 ¼ 0.11; P ¼ 0.0665, t40 ¼ 1.89; respectively), whereas time spent probing on imidacloprid-treated plants was significantly less than on water- and cyantraniliprole-treated plants at 2, 6 and 10 days after treatment (P ¼ 0.0005, t32 ¼ 3.88; P < 0.0001, t49 ¼ 13.65; P < 0.0001, t40 ¼ 12.64; respectively compared to water, and P < 0.0001, t32 ¼ 4.50; P < 0.0001, t49 ¼ 11.18; P < 0.0001, t40 ¼ 10.42; respectively compared to cyantraniliprole) (Table 2). Significant treatment effects on the mean durations of the 1st and 2nd probes by F. fusca were only observed 6 days after treatment (Table 2). The duration of the 1st probe was significantly shorter on cyantraniliprole- and imidacloprid-treated plants than on water treated plants 6 days after treatment (P ¼ 0.0035, t49 ¼ 3.07; P ¼ 0.0007, t49 ¼ 3.63; respectively). The duration of the 2nd probe was significantly shorter on imidacloprid-treated plants than on water-treated plants (P ¼ 0.0237, t49 ¼ 2.34),

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however, on cyantraniliprole-treated plants it was not significantly different from either water- or imidacloprid-treated plants (P ¼ 0.4393, t49 ¼ 0.78; P ¼ 0.1293, t49 ¼ 1.54; respectively) (Table 2). Abnormal waveforms were produced by F. fusca in all treatments but significant effects of treatment on the number of abnormal waveforms were observed at 6 and 10 days after treatment but not at 2 days after treatment (Table 2). The number of abnormal waveforms was significantly higher on cyantraniliproletreated plants than on either water- or imidacloprid-treated plants at both 6 and 10 days post-treatment (P ¼ 0.0125, t49 ¼ 2.59; P ¼ 0.0014, t40 ¼ 3.43; respectively compared to water, and P ¼ 0.0022, t49 ¼ 3.24; P ¼ 0.0384, t40 ¼ 2.14; respectively compared to imidacloprid) but not at 2 days after treatment (P ¼ 0.0656, t32 ¼ 1.91 and P ¼ 0.7987, t32 ¼ 0.26; respectively). There were no significant differences between the imidacloprid and water treatments at 2, 6 or 10 days after treatment (P ¼ 0.0947, t32 ¼ 1.72; P ¼ 0.6416, t49 ¼ 0.47; P ¼ 0.1885, t40 ¼ 1.34; respectively). The duration of abnormal waveforms was significantly affected by treatment at 6 days post-treatment but not at 2 and 10 days post-treatment. At 6 days post-treatment neither the cyantraniliprole nor the imidacloprid treatments differed significantly from the water-treated control in the duration of abnormal waveforms produced by F. fusca (P ¼ 0.3635, t10 ¼ 0.95; P ¼ 0.0542, t10 ¼ 2.18). However, the duration of abnormal waveforms was significantly shorter in imidacloprid- than on cyantraniliproletreated plants (P ¼ 0.0060, t10 ¼ 3.47). (Table 2). The effects of treatment on probing by F. occidentalis over the 10day period following treatment application (Table 1) were only significant for total number of probes, total time probing, and number of abnormal waveforms. Significant treatment effects were not observed for duration of 1st probe, duration of 2nd probe, or total duration of abnormal waveforms (Table 1). The number of probes was significantly less on imidaclopridthan on water-treated plants (P < 0.0001, t99 ¼ 4.61) and on cyantraniliprole-treated plants (P ¼ 0.0068, t99 ¼ 2.76) but did not differ between cyantraniliprole- and water-treated plants (P ¼ 0.0732, t99 ¼ 1.81). The total time spent probing was significantly less on imidacloprid- than on water-treated plants (P ¼ 0.0003, t99 ¼ 3.71) but did not differ significantly cyantraniliprole- and water-treated plants (P ¼ 0.0680, t99 ¼ 1.85) or cyantraniliprole- and imidacloprid-treated plants (P ¼ 0.0738, t99 ¼ 1.81). There were significantly more abnormal waveforms recorded on cyantraniliprole- than on water-treated plants (P ¼ 0.0064, t99 ¼ 2.79), and the number on imidacloprid-treated plants was intermediate to, and did not differ significantly from water- or cyantraniliprole-treated plants (P ¼ 0.2193 t99 ¼ 1.24; P ¼ 0.1115, t99 ¼ 1.61; respectively). The effect of treatment on mean number of probes by F. occidentalis during each post-treatment time interval was significant at 6 and 10 days after treatment, but not at 2 days after treatment (Table 2). Mean numbers of probes were significantly less on cyantraniliprole- than on water-treated plants at 6 (P ¼ 0.0061, t20 ¼ 3.07) but not at 2 or 10 days after treatment (P ¼ 0.4214, t28 ¼ 1.80; P ¼ 0.3900, t45 ¼ 0.87; respectively). On imidacloprid-treated plants, the mean number of probes was significantly less than on water-treated plants at both 6 and 10 days after treatment (P ¼ 0.0018, t20 ¼ 3.60; P ¼ 0.0011, t45 ¼ 3.50; respectively) and significantly less than on cyantraniliprole-treated plants 10 days after treatment (P ¼ 0.0109, t45 ¼ 2.65). The total time F. occidentalis spent probing differed significantly among treatments at 6 and 10 days post-treatment but not at 2 days post-treatment (Table 2). At 6 days post-treatment, F. occidentalis

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Table 3 Proportion of E. sonchifolia plants infected by thrips sampled from cohorts of infected adults released into field cages. Year

Release daya

F. fusca

2011

7 14 7ac 7b 14a 14b

0.77 0.33 0.20 0.07 0.07 0.40

2012

(22)b (15) (15) (15) (15) (10)

F. occidentalis 0.50 0.93 0.53 0.67 0.60 0.73

(8) (15) (15) (15) (15) (15)

a Corresponds to the group of thrips that were released onto the caged banana pepper plants 7 or 14 days after treatments were applied. b Proportion of plants infected (total number of plants). 5 putatively viruliferous thrips were caged with each plant. c 2012 Thrips were released on 2 dates (see text): a. corresponds to 1st release day and b. to 2nd release day.

spent significantly less time probing cyantraniliprole- and imidacloprid-treated plants than water-treated plants (P ¼ 0.0105, t20 ¼ 2.82; P ¼ 0.0015, t20 ¼ 3.69; respectively), and time spent probing did not differ between cyantraniliprole- and imidaclopridtreated plants (P ¼ 0.2508, t20 ¼ 1.18). At 10 days post-treatment, significantly less time was spent probing imidaclopridetreated than water-treated plants (P ¼ 0.0375, t45 ¼ 2.14) and the time spent probing cyantraniliprole-treated plants was intermediate to, and did not differ significantly from, the water-treated or imidacloprid-treated plants (P ¼ 0.5173, t45 ¼ 0.65; P ¼ 0.1409, t45 ¼ 1.50; respectively). Neither the 1st nor the 2nd probes by F. occidentalis differed significantly in duration among treatments in recordings at 2, 6, and 10 days post-treatment. Abnormal waveforms were observed in all treatments except the water-treated control at 2 days posttransplant (Table 2). The numbers of abnormal waveform events were very low, and overall treatment effects were not significant at 2, 6 or 10 days post-treatment. The number of abnormal waveforms was only significantly different between recordings from imidacloprid- and water-treated plants 2 days after treatment (P ¼ 0.0463, t28 ¼ 2.09). No significant differences in the duration of abnormal waveform events were observed among treatments at 2 and 6 days post-treatment (Table 2). LS-means separation could not be conducted on the 10-day post-treatment for this parameter because too few observations were available for this variable.

Table 4 Effect of transplant drench application of water, cyantraniliprole, or imidacloprid on transmission of TSWV to Capsicum annuum by Frankliniella fusca and F. occidentalis in small-plot field trials. Year

Treatment

2011 Water Cyantraniliprole Imidacloprid 2012 Water Cyantraniliprole Imidacloprid

Based on the infection of E. sonchifolia plants by samples of F. fusca and F. occidentalis from the cohorts that were released into the cages on each of the release dates, the released thrips were able to transmit TSWV in both years (Table 3). The proportions of infected plants varied between the 7 and 14 day release dates and were generally higher for F. occidentalis than F. fusca in 2011 and 2012. 3.2.1. Frankliniella fusca In 2011 the likelihood of infection was significantly lower in the cyantraniliprole- than in the water-treated control plots when F. fusca were released 7 days after application (Tables 4 and 5). However, when thrips were released 14 days after treatment there was no significant difference between the water and cyantraniliprole treatments. In the 2012 experiment, applications of cyantraniliprole did not significantly reduce the likelihood of TSWV infection as compared to the water-treated control when F. fusca were released at 7 days post-treatment, but the reduction was significant when F. fusca was released at 14 days post-treatment.

14 day release

F. fusca

F. occidentalis F. fusca

F. occidentalis

0.38 0.16 0.0 0.23 0.17 0.02

0.26 0.05 0.16 0.50 0.60 0.58

0.15 0.03 0.08 0.21 0.20 0.20

(40) (38)a (40) (44) (52) (45)a,b

(38) (39)a (38) (56) (60) (59)

0.08 0.11 0.0 0.24 0.08 0.0

(40) (36) (39) (38) (50)a (43)

(40) (40) (38) (57) (60) (60)

Proportion of plants infected (total number of plants). Data for F. fusca and F. occidentalis were obtained in separate experiments and were analyzed separately. Treatment separations within species and release date based on odds ratio contrasts shown in Table 5. a Different from water. b Different from cyantraniliprole.

In 2012, imidacloprid significantly reduced the likelihood of infection relative to the water-treated control and relative to the cyantraniliprole treatment when F. fusca were released 7 days after treatments (Tables 4 and 5). None of the plants in the imidacloprid treatment became infected following release of F. fusca at 7 or 14 days after treatment in 2011 or when released at 14 days after treatment in 2012; hence, contrasts between imidacloprid and either cyantraniliprole or water could be conducted. 3.2.2. Frankliniella occidentalis In the 2011 experiment, the effect of transplant water treatments on TSWV likelihood of infection was significant when F. occidentalis were released at 7 days post-treatment (Tables 4 and

Table 5 Odds ratios for contrasts involving effects of cyantraniliprole and imidacloprid on infection of banana pepper by Tomato spotted wilt virus transmitted by Frankliniella fusca or F. occidentalis released into field cages 7 or 14 days following soil application in transplant water. Contrasta

Cyantraniliprole vs water

3.2. Small plot field trials

7 day release

Odds ratiob

Chi square (df ¼ 1)

P

0.348 1.542 0.712 0.280 0.077

3.6156 0.2920 0.4388 3.8786 5.6900

0.0572 0.5889 0.5077 0.0489 0.0171

0.109

4.2601

0.0390

F. occidentalis 2011 7 0.151 14 0.145 2012 7 1.500 14 0.938 2011 7 0.632 14 0486 2012 7 1.360 14 0.938 2011 7 4.177 14 3.342 2012 7 0.907 14 1.000

5.3793 3.0456 1.1670 0.0199 0.6762 0.9346 0.6713 0.0199 2.9111 1.0496 0.0691 0.0000

0.0204 0.0810 0.2800 0.8879 0.4109 0.3337 0.4126 0.8879 0.0880 0.3056 0.7926 1.0000

Year

2011 2012

Imidacloprid vs water

Release date F. fusca 7 14 7 14 7

2012 Imidacloprid vs Cyantraniliprole Cyantraniliprole vs water

Imidacloprid vs water

Imidacloprid vs Cyantraniliprole

7 2012

a Contrasts conducted in Logistic Regression; contrasts for imidacloprid vs water and for imidacloprid vs cyantraniliprole not available for the F. fusca experiments at 7 and 14 days after treatment in 2011 or at14 days after treatment in 2012 because no plants in the imidacloprid treatment became infected. Statistically significant contrasts indicated in bold. b Ratio of odds of plant becoming infected in first treatment listed to the odds of plant becoming infected in the second treatment listed in the contrast.

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5). The likelihood of infection was significantly lower in the cyantraniliprole treatment than in the water-treated control. The likelihood of infection in the imidacloprid-treated plots was intermediate between the cyantraniliprole-treated and the watertreated plots, and did not differ significantly from either. As with F. fusca, the likelihood of infection following release of F. occidentalis at 14-days post-transplant was low in both the treated and control plots. None of the treatment effects were significant. In the 2012 experiment, neither the cyantraniliprole nor imidacloprid treatments significantly reduced the likelihood of TSWV infection relative to the water-treated control when the F. occidentalis were released at 7 or 14 days post-treatment (Tables 4 and 5). 4. Discussion In previous greenhouse experiments, cyantraniliprole applied as a soil drench reduced transmission of TSWV to banana pepper plants by F. fusca but not by F. occidentalis at rates ranging from 1.43 to 4.41 mg active ingredient per plant (Jacobson and Kennedy, 2011). These results were observed in the absence of elevated mortality by either species, suggesting that cyantraniliprole may affect their feeding behavior differently. Although our EPG results reveal significant effects of both cyantraniliprole and imidacloprid treatments on probing/feeding behavior by both F. fusca and F. occidentalis, these effects were quantitative rather than qualitative in nature and, with the exception of total number of probes by F. fusca, were variable depending on number of days posttreatment. Our EPG results demonstrate that cyantraniliprole applied as a soil drench at 10 mg a.i. per plant altered feeding behavior relative to water-treated controls by both F. fusca and F. occidentalis, but the differences between species were relatively minor (Table 2). The total number of probes by F. fusca was reduced on cyantraniliproletreated plants at 2, 6, and 10 days post-treatment, whereas the number of probes by F. occidentalis was significantly affected only at 6 days post-treatment. In addition, significant reductions in total time spent probing by both species were observed on cyantraniliprole-treated plants at 6 but not at 2 or 10 days post treatment. However, the cyantraniliprole treatment resulted in a significant reduction in duration of 1st probe by F. fusca but not F. occidentalis at 6 days post-treatment, with no such effect observed on either species at 2 and 10 days post-treatment. Previous studies have demonstrated differential effects on probing/feeding and settling behavior between F. fusca and F. occidentalis on plants treated with imidacloprid (Groves et al., 2001a; Joost and Riley, 2005). Our EPG results demonstrating significant reductions in total number of probes and total time probing by F. fusca on imidacloprid-treated plants are consistent with the findings of Groves et al. (2001a) and Joost and Riley (2005). However, our results with F. occidentalis differ from those of Joost and Riley (2005), who found significant increases in frequency and duration of probes by F occidentalis on imidacloprid-treated tomato plants. In contrast, we observed a significant reduction in total number of probes but no difference in the total time probing by F. occidentalis on imidacloprid-treated plants. The reasons for this inconsistency are not known but may be related to differences in rates of imidacloprid used and possibly differences in the suitability of pepper and tomato as hosts for F. occidentalis. Joost and Riley (2005) used 7.81 and 41.55 mg a.i./plant, whereas we used a much higher rate of 13.2 mg a.i./plant in our study, which may account for the negative effect on number of probes by F. occidentalis that we observed. Finally, the number of abnormal waveform events produced by F. fusca was greater in the cyantraniliprole than in the water treatment at 6 and 10 days post-treatment but no such effect was observed for F. occidentalis. Abnormal waveform events occurred in

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all treatments and were produced by both F. fusca and F. occidentalis. They occurred more frequently on cyantraniliproletreated than control plants for F. fusca and F. occidentalis, suggesting that their increased occurrence reflects a response by the thrips to the insecticide treatments. These waveforms typically occurred during prolonged probes, and are characterized by a lower and more irregular frequency than in the typical probing and feeding behavior waveforms in Kindt et al. (2003) and Stafford et al. (2011). The form, frequency and amplitude of these waveforms were variable among individuals, but generally took the form of those displayed in Fig. 1. The specific probing events associated with these waveforms are not known, and cannot be determined from this study because video recordings were not taken to correlate physical movements and behavior with the waveforms. As with our EPG experiments, the results of our field cage experiments reveal considerable variation in the effects of cyantraniliprole on TSWV transmission to pepper. Cyantraniliprole reduced the likelihood of TSWV transmission by both F. fusca and F. occidentalis when the vectors were released at 7 days after treatment in 2011 but not in 2012. When the vectors were released at 14 days after treatment, cyantraniliprole reduced the likelihood of transmission by F. fusca relative to the water-treated control in 2012 (Tables 4 and 5) but not in 2011. No effects of cyantraniliprole on likelihood of transmission by F. occidentalis were observed when they were released at 14 days after treatment. The effects of imidacloprid on transmission were more consistent across years and release dates, with a significant reduction in likelihood of infection when F. fusca was released at 7 days after treatment in 2012 and no infections occurring in the imidacloprid treatments when F. fusca was released at 7 days after treatment in 2011 and at 14 days after treatment in 2011 and 2012. In contrast, the imidacloprid treatment did not reduce the likelihood of infection when F. occidentalis was the vector in any of our experiments. A reduction of TSWV transmission to imidacloprid treated plants by F. fusca but not F. occidentalis has been previously reported in several crops (Csinos et al., 2001; Joost and Riley, 2005; Kindt, 2004; Kindt et al., 2003, 2006). Our EPG results document reductions in probing on cyantraniliprole-treated plants by both F. fusca and F. occidentalis, as well as substantial variation in the probing responses of individual thrips to treated plants. The results of our field experiments similarly revealed significant reductions in the likelihood of TSWV infection in pepper treated with cyantraniliprole when transmitted by F. fusca, and F. occidentalis in some but not all experiments. This variation may reflect the distribution of cyantraniliprole within treated plants over time, as well as variation in other potential host plant acceptance behaviors, such as dispersal from a plant in response to an insecticide-mediated stimulus. Responses of this type are likely to be moderated or masked in situations in which thrips are confined to the plants, as is the case for all EPG studies or within cages as in our field experiments. Together our findings along with those of Jacobson and Kennedy (2011) suggest that although soil drench applications of cyantraniliprole have the potential to suppress TSWV transmission to pepper under some circumstances, the levels of suppression are likely to be variable. Such variation is consistent with the performance of other measures, including commercially available insecticide treatments, frequently used in multi-tactic approaches to manage TSWV, which vary in effectiveness depending on crop, application timing, vector species, inoculum pressure, relative importance of primary and secondary spread, and other factors yet to be defined (Coutts and Jones, 2005; Csinos et al., 2001; Culbreath et al., 2003; Pappu et al., 2000). In this context, additional research to characterize factors contributing to variation in performance of cyantraniliprole in reducing virus spread may be warranted.

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Acknowledgments We would like to thank Carol Berger, Damon D’Ambrosio, Daniel Grist, and Amanda Beaudoin for their assistance with various aspects of the field and EPG trials conducted in this study, and Robert Williams of DuPont for providing the CyazypyrÔ used in these experiments. We would also like to thank Elaine Backus, Tim Ebert, Joy Smith and Tom Chappell for their guidance and assistance with managing and analyzing EPG data. We appreciate the financial support for this research from DuPont and from NIFA Pest Management Alternatives Program (grant project NC09807). References Aramburu, J., Martí, M., 2003. The occurrence in north-east Spain of a variant of Tomato spotted wilt virus (TSWV) that breaks resistance in tomato (Lycopersicon esculentum) containing the Sw-5 gene. Plant Pathol. 52, 407. Backus, E.A., Cline, A.R., Ellerseik, M.R., Serrano, M.S., 2007. Lygus Hesperus (Hemiptera: Miridae) feeding on cotton: new methods and parameters for analysis of non-sequential electrical penetration graph data. Ann. Entomol. Soc. Am. 100, 296e310. Burt, A., Karr, D., 2008. DuPont and Syngenta Enter into Crop Protection Technology Exchange. http://vocuspr.vocus.com/VocusPR30/Newsroom/Query.aspx? SiteName¼DuPontNew&Entity¼PRAsset&SF_PRAsset_PRAssetID_ EQ¼110201&XSL¼PressRelease&Cache. Butler, C.D., Walker, G.P., Trumble, J.T., 2012. Feeding disruption of potato psyllid, Bactericera cockerelli, by imidacloprid as measured by electrical penetration graphs. Entomol. Exp. Appl. 142, 247e257. Cameron, R., Lang, E.B., Annan, I.B., Portillo, H.E., Alvarez, J.A., 2013. Use of fluorescence, a novel technique to determine reduction in Bemisia tabaci (Hemiptera: Aleyrodidae) nymph feeding when exposed to Benevia and other insecticides. J. Econ. Entomol. 106, 597e603. Castle, S., Palumbo, J., Nilima, P., 2009. Newer insecticides for plant virus disease management. Virus Res. 141, 131e139. Chatzivassiliou, E.K., 2008. Management of the spread of tomato spotted wilt virus in tobacco crops with insecticides based on estimates of thrips infestation and virus incidence. Plant Dis. 92, 1012e1020. Cordova, D., Benner, E., Sacher, M., Rauh, J., Sopa, J., Lahm, G., Selby, T., Stevenson, T., Flexner, L., Gutteridge, S., Rhoades, D., Wu, L., Smith, R., Tao, Y., 2006. Anthranilic diamides: a new class of insecticides with a novel mode of action, ryanodine receptor activation. Pestic. Biochem. Physiol. 84, 196e214. Coutts, B.S., Jones, R.A.C., 2005. Suppressing spread of Tomato spotted wilt virus by drenching infected source or healthy recipient plants with neonicotinoids insecticides to control thrips vectors. Ann. Appl. Biol. 146, 95e103. Csinos, A.S., Pappu, H.R., McPherson, R.M., Stephenson, M.G., 2001. Management of Tomato spotted wilt virus in flue-cured tobacco with acibenzolar-S-methyl and imidacloprid. Plant Dis. 85, 292e296. Culbreath, A.K., Todd, J.W., Brown, S.L., 2003. Epidemiology and management of spotted wilt of peanut. Ann. Rev. Phytopathol. 41, 53e75. Diaz-Montano, J., Fuchs, M., Nault, B.A., Shelton, A.M., 2010. Evaluation of onion cultivars for resistance to onion thrips (Thysanoptera: Thripidae) and Iris Yellow Spot Virus. J. Econ. Entomol. 103, 925e937. Gonzales-Coloma, A., Gutierrez, C., Hubner, H., Achenbach, H., Terrero, D., Fraga, B.M., 1999. Selective insect antifeedant and toxic action of ryanoid diterpenes. J. Agric. Food Chem. 47, 4419e4424. Greenough, D.R., Black, L.L., Bond, W.P., 1990. Aluminum-surfaced mulch e an approach to the control of Tomato Spotted Wilt Virus in Solanaceous crops. Plant Dis. 74, 805e808. Groves, R.L., Sorenson, C.E., Walgenbach, J.F., Kennedy, G.G., 2001a. Effects of imidacloprid on transmission of tomato spotted wilt tospovirus to pepper, tomato and tobacco by Frankliniella fusca Hinds (Thysanoptera: Thripidae). Crop Prot. 20, 439e445. Groves, R.L., Walgenbach, J.F., Moyer, J.W., Kennedy, G.G., 2001b. Overwintering of Frankliniella fusca Hinds (Thysanoptera: Thripidae) on winter annual weeds infected with tomato spotted wilt tospovirus (TSWV) and patterns of movement of TSWV into susceptible hosts. Phytopathology 91, 891e899. Hannig, G.T., Ziegler, M., Marcon, P.G., 2009. Feeding cessation effects of chlorantraniliprole, a new anthranilic diamide insecticide, in comparison with several insecticides in distinct chemical classes and mode-of-action groups. Pest Manag. Sci. 65, 969e974. Herbert Jr., D.A., Malone, S., Aref, S., Brandenburg, R.L., Jordan, D.L., Royals, B.M., Johnson, P.D., 2007. Role of insecticides in reducing thrips injury to plants and incidence of tomato spotted wilt virus in Virginia market-type peanut. J. Econ. Entomol. 100, 1241e1247.

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