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Susceptibility of field populations of the fall armyworm (Lepidoptera: Noctuidae) from Florida and Puerto Rico to purified Cry1F protein and corn leaf tissue containing single and pyramided Bt genes.

Transgenic corn hybrids expressing Bacillus thuringiensis (Bt) proteins were initially developed to reduce injury from corn stalk borers such as the European corn borer, Ostrinia nubilalis (Hiibner) and southwestern corn borer, Diatraea grandiosella (Dyar). Fall armyworm, Spodoptera frugiperda (J. E. Smith), is an important pest of corn in both North and South America (Pashley et al. 1985; Pashley 1986; Buntin et al. 2004; Chilcutt et al. 2007). Several studies have evaluated the field efficacy of first generation single gene Bt corn products (e.g. YieldGard[R] Corn Borer, Herculex[R]I) against S. frugiperda (Buntin et al. 2000; 2004; Buntin 2008; Siebert et al. 2008). Results of these studies showed that the single gene Bt corn also could suppress S. frugiperda but the suppression levels were usually not high enough to qualify as "high dose". For this reason, S. frugiperda is not listed as a target species of the first generation Bt corn technologies except Herculex[R]I expressing the Cry1F protein (US EPA 2001a).

Herculex[R]I Cry1F corn was first registered in 2001 in the United States and later became commercially available in the United States and Puerto Rico in 2003 to control stalk borers and some Noctuidae moths including S. frugiperda. This insect has been reported as the most important corn pest in Puerto Rico (US EPA 2007; Storer et al. 2010). Unfortunately, field resistance to Cry1F corn was observed in S. frugiperda populations in Puerto Rico in 2006 (Storer et al. 2010). This became the first example of field resistance to commercial Bt crops in the world (US EPA 2007; Matten et al. 2008; Storer et al. 2010). Besides intensive plantings of Cry1F corn during the 3 yr in Puerto Rico, several other factors might have contributed to the development of field resistance (US EPA 2007; Storer et al. 2010; Huang et al. 2011). To delay resistance development and broaden the target spectrum, a gene-pyramiding strategy has been utilized to develop transgenic plants that express multiple Bt proteins with dissimilar modes of action for targeting a same group of insect pests (Ghimire et al. 2011). The first commercialized pyramided Bt corn technologies for managing lepidopteran pests in the United States included Genuity[R]VT Double Pro[TM], Genuity[R]VT Triple Pro[TM], Genuity[R] SmartStax[TM], and Agrisure[R] Viptera[TM] 3111. Compared to the first generation single-gene Bt corn, the pyramided Bt corn products are more effective for controlling some Noctuidae species including S. frugiperda (Burkness et al. 2010) and thus S. frugiperda is listed as a target in all pyramided Bt corn traits that have been commercialized for managing above-ground lepidopteran corn pests in the United States (US EPA 2009; 2010; Monsanto 2012; Syngenta 2012).

During 2011, 2 field populations of S. frugiperda were established from larvae collected from corn fields in Florida and Puerto Rico, respectively. Preliminary studies showed that the Puerto Rico population was highly resistant to Cry1F corn plants, while the Florida population was still susceptible to the Cry1F corn. Therefore, these 2 populations of S. frugiperda should provide great value for analyzing cross-resistance to other Bt corn technologies, especially to the recently commercialized pyramided Bt corn. The objectives of this study were to 1) document the resistance of the field population of S. frugiperda from Puerto Rico to purified Cry1F protein and commercial Cry1F corn and 2) to determine the cross-resistance of this population to pyramided corn products.

MATERIALS AND METHODS

Insect Sources

Two field populations of S. frugiperda were established from larvae collected from corn fields in Florida and Puerto Rico, respectively, in 2011. The Florida population (FL) was initiated from 96 larvae sampled from Hendry County in south Florida and the Puerto Rico population (PR) was developed from >300 larvae collected in southern Puerto Rico. Field-collected larvae were reared individually on a meridic diet (Ward's Stonefly Heliothis diet, Rochester, NY) in 30-ml plastic cups (Fill-Rite, Newark, NJ) until the pupal stage. The larval-rearing cups were held in 30-well trays (Bio-Serv, Frenchtown, NJ) and placed under room conditions until pupation. Pupae of each population were placed in 3.8-L paper containers (Huhtamaki Foodservice, De Soto, KS) containing ~100g of vermiculite (Sun Gro, Pine Bluff, AR) for adult emergence, mating, and oviposition. Insect populations had been maintained in the laboratory for 2 generations for FL and 3 generations for PR when this study was initiated.

Susceptibility of S. frugiperda was evaluated using 2 approaches: 1) a diet incorporating bioassay with purified Cry1F protein and 2) testing on leaf tissue of Bt and non-Bt corn hybrids. There were 2 independent trials for each test approach. For the diet incorporation bioassays, the first trial used the original 2 populations (FL and PR) that were established from larvae collected from fields without further selection in the laboratory. In the first trial with leaf tissue bioassays, larval mortality was evaluated for 3 insect populations including FL, PR, and an [F.sub.1] population (FL x PR) that was generated by crossing FL and PR. Results of the first trial showed that compared to FL, the PR population was highly resistant to both the purified Cry1F protein and Cry1F corn leaf tissue (see below). After the first trial with Cry1F protein and corn leaf tissue, the original PR larvae were selected on Cry1F corn (Pioneer 31D59) leaf tissue for 2 generations. In the selection process, 2-3 pieces of leaf tissue were placed in each well of 32-well C-D International trays (Bio-Ba-32, C-D International, Pitman, NJ). Approximately 5-10 newly hatched larvae were released in each well. For each generation, >1000 neonates were selected on Cry1F corn leaf tissue. After 7 days, the survivors were transferred into the diet. After each selection, approximately 120-180 survivors were reared until the next generation. If the number of survivors was more than enough (e.g. >180 larvae), only the survivors with a relatively bigger body size were used to develop the next generation. The Cry1F corn leaf tissue selected-PR populations were then backcrossed with the FL population and reselected for Cry1F resistance in [F.sub.2] generations on Cry1F corn leaf tissue. The procedures of the reselections for Cry1F resistance in the [F.sub.2] generations of the backcrosses were the same as described above. Thereafter, the backcrossed and reselected population was referred as Cry1F-RR. The Cry1F-RR population had been continuously selected on Cry1F corn leaf tissue for at least 2 more generations before it was used for this study. In addition, another [F.sub.1] population (Cry1F-RS) was developed by crossing individuals from FL and Cry1F-RR. In the second trial, susceptibility of S. frugiperda was evaluated for all 3 populations including FL, Cry1F-RR, and Cry1F-RS in both diet incorporation and leaf tissue bioassays.

Source of Cry1F Protein and Corn Leaf Tissue

In the diet incorporation bioassays, purified trypsin-activated (99.9%) Cry1F protein was obtained from Case Western Reserve University, Cleveland, OH. The Cry proteins were produced using recombinant Escherichia coli culture and were subsequently activated with trypsin. The activated Cry proteins were lyophilized before they were used in the bioassays. The purity of Cry1F proteins was determined using high-performance liquid chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis (Pusztai-Carey et al. 1995; Masson et al. 1998).

In the leaf tissue tests, susceptibility of S. frugiperda was evaluated on leaf tissue of 5 non-Bt and 7 Bt corn hybrids (Table 1). The 7 Bt corn hybrids represent 5 Bt corn traits, which include 1 single-gene Bt corn product, Herculex[R]I and 4 pyramided Bt corn products, Genuity[R]VT Double Pro[TM], Genuity[R]VT Triple Pro[TM], Genuity[R] SmartStax[TM], and Agrisure[R] Viptera[TM] 3111. Herculex[R]I contains a single Bt gene, Cry1F (Event TC1507), effective for above-ground lepidopteran insects. VT Double Pro[TM] expresses 2 Cry proteins, Cry1A.105 and Cry2Ab2 (Event MON89034) and both proteins are effective against above-ground lepidopteran species including S. frugiperda (Monsanto 2012). VT Triple Pro[TM] contains the same 2 Cry proteins in VT-2P plus Cry3Bb1 (MON88017) which is effective against below-ground corn rootworms Diabrotica spp. (Coleoptera: Chrysomelidae) (Monsanto 2012). SmartStax[TM] produces 6 Bt proteins including the 3 Bt proteins of VT Triple Pro[TM] plus Cry1F (Event TC1507) targeting lepidopteran species and Cry34/35Ab1 (Event DAS-59122) against rootworms (Monsanto 2012). Viptera[TM] 3111 expresses 3 Bt proteins including Vip3A (Event MIR162) and Cry1Ab (Event Bt11) for controlling lepidopteran species and mCry3A (Event MIR604) for managing rootworms (DiFonzo & Collen 2012). The 5 non-Bt corn hybrids were genetically closely related to 1 or 2 of the 7 Bt corn hybrids. In each of the 2 trials, larval morality of S. frugiperda was evaluated on corn leaf tissue of 5 Bt corn hybrids representing 5 Bt corn technologies along with 2 (1st trial) or 3 (2nd trial) non-Bt corn hybrids (Table 1). Expression (or not expression) of Bt proteins in plants was confirmed using ELISA-based assays (EnviroLogix, Quantiplate[TM] kits, Portland, ME).

Diet Incorporation Assays

Larval susceptibility of S. frugiperda to purified Cry1F protein was individually assayed using a diet incorporation procedure in 128-cell trays (C-D International, Pitman, NJ). In each bioassay, 6-8 Cry1F concentrations were used. Cry1F concentrations used in each bioassay were slightly different depending on the insect population and amount of Cry1F protein available. In the first trial, Cry1F concentrations of 0, 0.1, 0.316, 1, 3.16, 10, and 31.6[micro]g/g were used to assay both FL and PR populations. Based on the results of the first trial, Cry1F concentrations used in the 2nd trial were modified to 0, 0.0316, 0.1, 0.316, 1, 3.16, and 10[micro]g/g in assaying FL. In addition, concentrations of 31.6 (for both PR and Cry1F-RS) and 100]g/g (for PR only) were also included in the second bioassays. To prepare the appropriate concentrations of Bt diet, purified Cry1F protein was first suspended in distilled water at the room temperature and stirred completely using an iron stick to ensure that the protein was uniformly distributed in the solution. The Cry1F solutions were then mixed with a meridic diet (WARD'S Stonefly Heliothis diet) just prior to placing the diet into individual cells of the 128-cell trays. In the bioassay, approximately 1 g of treated diet was placed into each cell. One neonate (<24 h) was released on the diet in each cell. After larval inoculation, cells were covered with vented lids (C-D International, Pitman, NJ). The bioassay trays were placed in environmental chambers maintained at 28[degrees]C, 50% RH, and a 16:8 (L:D) h photoperiod. Larval mortality was recorded on the 7th day after inoculation. Larvae were considered dead if they did not respond after being touched with a camel hair bush. In a bioassay, each combination of insect population by Cry1F concentration was replicated 4 times with 16-32 larvae in each replicate.

Leaf Tissue Test

Fully expanded leaf tissues of Bt and non-Bt corn hybrids were removed from greenhouse grown V5-V8 stage plants. In the bioassays, 2-3 pieces of leaf tissue were placed in each well of a 32-well C-D International tray (Bio-Ba-32, C-D International, Pitman, NJ). In each of the 2 trials, 4 neonates (<24 h old) of each of 3 populations were placed on the surface of the leaf tissue in each well. Bioassay trays containing leaf tissues and neonates were placed in growth chambers maintained at the same conditions as for the diet incorporation bioassays. Larval mortality was recorded on the 7th day after release of neonates. As mentioned above, larvae were considered dead if they did not respond after being touched with a camel hair bush. In each trial, there were 4 replications for each combination of corn hybrid and insect population and each replication included 32 neonates in 8 wells (n = 128).

Data Analysis

In the diet incorporation bioassay, larval mortality of S. frugiperda at a Cry1F concentration was corrected with mortality on the control diet using the method as described in Abbott (1925). The corrected concentration/mortality data were then subjected to a probit analysis to determine the Cry1F concentration that produced a 50% mortality value ([LC.sub.50]) and the corresponding 95% confidence interval (CI) (Finney 1971; SAS Institute 2010). For each bioassay, the Cry1F concentrations used in the probit analysis included the highest concentration that produced zero mortality, the lowest concentration that resulted in 100% mortality, and all results between those extremes (Huang et al. 2007). In the bioassays with PR and Cry1F-RR, no significant larval mortality was observed even at the highest Cry1F concentrations tested, and thus the [LC.sub.50] values for these 2 populations were considered to be greater than the highest Cry1F concentrations used in the bioassays. Resistance ratios for each Cry protein were calculated using the [LC.sub.50] value of PR, Cry1F-RR, or Cry1F-RS divided by the [LC.sub.50] of the FL population.

Because the [LC.sub.50] values of the PR and Cry1FRR populations couldn't be calculated with the probit analysis, larval mortality data, after transformed by arcsine [(x).sup.0.5], were also subjected to a two-way analysis of various (ANOVA) with Cry1F concentration and insect population as the 2 main factors. Similarly, in the 2 trials using corn leaf tissue, percent larval mortalities were first transformed by arcsine [(x).sup.0.5] and then analyzed using a 2 way ANOVA with corn hybrid and insect population as the 2 main factors (SAS Institute, 2010). Treatment means in all ANOVAs were separated with LSMEANS test at [alpha] = 0.05 level (SAS Institute, 2010).

In addition, the dominance level of Cry1F resistance in S. frugiperda was estimated using 2 approaches. The first approach involved the use of the Stone's dominance "D" value. The [LC.sub.50] values estimated in the 2nd diet incorporation bioassays were used to calculate the dominance "D" value using the formula described in Stone (1968). The "D" value ranges from -1 to 1: a value of -1 indicating resistance is completely recessive; a value of 0 suggesting resistance is additive; and a value of 1 implying resistance is completely dominant. The dominance level of Cry1F resistance in S. frugiperda was also estimated as "effective dominance", [D.sub.ML], using the method as described in Bourguet et al. (2000). [D.sub.ML] ranges between 0 and 1. [D.sub.ML] = 0 refers to a completely recessive resistance and [D.sub.ML] = 1 means the resistance is completely dominant. In this study, [D.sub.ML] was estimated using the mortality data of the 3 insect populations recorded in each of the 2 trials on corn leaf tissue of 4 Bt corn technologies. [D.sub.ML] for Viptera[TM] 3111 couldn't be calculated because all insect populations exhibited 100% mortality on the Bt corn leaf tissue in both trials.

RESULTS

Susceptibility of Field Populations from Florida and Puerto Rico to Purified Cry1F Protein: Trial # 1

The FL population was susceptible to the purified Cry1F protein with a [LC.sub.50] of 0.23[micro]g/g and a 95% CI of 0.11-0.37[micro]g/g (Table 2). Relative to FL, PR was highly resistant to the Cry1F protein. No significant larval mortality ([less than or equal to] 13.7%, corrected mortality) of PR was observed across all the Cry1F concentrations assayed and thus the [LC.sub.50] value of this population was estimated to be > 31.6[micro]g/g, which corresponded a resistance ratio of >137-fold.

Two-way ANOVA showed that the main effects of both Cry1F concentration and insect populations on the 7-day larval mortality were significant (F = 31.31; df = 6, 41; p < 0.0001 and F = 308.16; df = 1, 41; p < 0.0001, respectively). The effect of the interaction of the 2 factors was also significant (F = 26.82; df = 6, 41; p < 0.0001). Significant larval mortality (50.2%) of the FL population occurred at 0.1 [micro]/g, the lowest concentration assayed, and the mortality reached 95.4% at 3.16 [micro]g/g and 100% at 10 [micro]g/g (Fig. 1). In contrast, Cry1F at all tested concentrations did not cause any significantly greater mortality to PR than those observed on non-Bt control diet.

Susceptibility of FL, Cry1F-RR, and Cry1F-RS Populations to Purified Cry1F Protein: Trial # 2

Similarly as observed in the first trial, the FL population was still susceptible to the purified Cry1F protein with a [LC.sub.50] of 0.13[micro]g/g and a 95% CI of 0.07-0.20[micro]g/g, which was not significantly different compared to the [LC.sub.50] value calculated in the first trial based on the overlapping of the 95% confident intervals (Table 2). The backcrossed and reselected population, Cry1F-RR, was also highly resistant to the purified Cry1F protein. Again, no significant mortality ([less than or equal to] 8.7%, corrected mortality) of Cry1F-RR was recorded at the tested concentration range (up to 100 [micro]g/g) and thus the [LC.sub.50] value was estimated to be > 100 [micro]g/g, which was at least 769-fold greater than the [LC.sub.50] of FL. The [LC.sub.50] value of Cry1F-RS, the F1 population of the cross between FL and Cry1F-RR, was 1.07[micro]g/g with a 95% CI of 0.76-1.50[micro]g/g, which was significantly greater than the [LC.sub.50] of FL based on the non-overlapping of the 95% confident intervals. However, the value of 1.07[micro]g/g was considerably less than the [LC.sub.50] of Cry1F-RR.

Two-way ANOVA also showed that effects of Cry1F concentration, insect population, and their interaction on 7-day larval morality were all significant (F = 56.79; df = 8, 72; p < 0.0001 for, F = 130.88; df = 2, 72; p < 0.0001, and F = 32.15; df = 13,72; p < 0.0001, respectively). Compared to the non-treated control diet, Cry1F at the tested concentrations did not result in any significant levels of mortality against the Cry1F-RR population, even at the highest concentration evaluated in the bioassays (100ug/g) (Fig. 1). In contrast, significant mortality (39.1%) was observed for the FL population at the lowest concentration tested (0.0316 [micro]g/g). Mortality of FL reached 94.6% at 1 [micro]g/g and 100% at 3.16 [micro]g/g. Mortality of the Cry1F-RS population at <1 [micro]g/g was low, between 11.3 (0.0316 [micro]g/g) and 30% (1.0 [micro]g/g). The mortality values were significantly less (P < 0.05) than those of the FL population, but in general were not significantly different compared to the mortalities observed for the Cry1F-RR population (P > 0.05). At [greater than or equal to] 3.16 [micro]g/g, mortality of Cry1F-RS increased significantly as the Cry1F concentration increased and reached 80.7% at 3.16 [micro]g/g and 96.6% at 10 [micro]g/g. The mortality of Cry1F-RS at 10 [micro]g/g was not significantly different from 100% that was observed for the FL population.

Susceptibility of FL, PR, and FL x PR Populations to Bt Corn Leaf Tissue: Trial # 1

The effect of corn hybrid, insect population, and their interaction on larval mortality at 7 days was significant (F = 82.42; df = 6, 63; p < 0.0001, F = 35.91; df = 2, 63; p < 0.0001, and F = 4.22; df = 12, 63; p < 0.0001, respectively). Larval mortality of the 3 insect populations on leaf tissue of the 2 non-Bt corn hybrids after 7 days varied significantly, ranging from 9.4% for PR to 66.4% for FL on DKC 67-86 (Fig. 2). Except for these 2 extremes, there was generally no significant difference in larval mortality on the 2 non-Bt corn hybrids. A high mortality (96.9%) of FL larvae was observed on leaf tissue of Herculex[R]I expressing the Cry1F protein, which was significantly greater than the mortality observed on the non-Bt corn leaf tissue. In contrast, the PR larvae appeared to be highly resistant to Cry1F corn leaf tissue, with a 7-day mortality of only 39.1%. This mortality level was similar to the average mortality (38.5%) of the 3 populations on the 2 non-Bt corn leaf tissue. The [F.sub.1] population of the cross between FL x PR was susceptible to Cry1F leaf tissue, producing a 7-day mortality of 83.6% (Fig. 2). This was significantly greater (P < 0.05) than that observed for PR but significantly less (P < 0.05) than the mortality of FL. However, all 3 insect populations were susceptible to leaf tissue of the 4 pyramided Bt corn hybrids. No survivors of FL were observed after 7 days on the 4 pyramided Bt corn hybrids. Mortality of the FL x PR population was also high on these pyramided Bt corn products (>95%), which was not significantly different (P > 0.05) than that observed for the FL population. PR larvae couldn't survive on Agrisure[R] Viptera[TM] 3111 leaf tissue, while a few larvae (e.g. 6.2-14.1%) of PR survived on the other 3 pyramided Bt corn hybrids (Genuity[R]VT MDouble Pro[TM], VT Double Pro[TM], and SmartStax[TM]).

Susceptibility of FL, Cry1F-RR, and Cry1F-RS Populations to Bt Corn Leaf Tissue: Trial # 2

As observed in the first trial, the effect of corn hybrid, insect population, and their interaction on larval mortality was all significant (F = 147.88; df = 7, 71; p < 0.0001, F = 120.67; df = 2, 71; P < 0.0001, and F = 21.27; df = 14, 71; p < 0 .0001, respectively). The 7-day larval mortality was in general similar (P > 0.05) on leaf tissue of the 3 non-Bt corn hybrids across the 3 insect populations with an average mortality of 36.3% (Fig. 2). Again, larval mortality of the FL population was high and not significantly different (P > 0.05) on the 5 Bt corn hybrids, ranging from 98.4-100%. The Cry1F-RS population was also susceptible to the 5 Bt corn hybrids with a mortality range of 93.0 to 100%. The mortality (93.0%) of Cry1F-RS on Herculex I was similar to that (94.5%) observed on the VT Double Pro[TM] but was significantly less than the mortalities (100%) on VT Triple Pro[TM], SmartStax, and Viptera 3111. The backcrossed and reselected Cry1F-RR population was also not able to survive on the Viptera 3111 hybrid. In contrast, larvae of the Cry1F-RR population survived well on the Cry1F corn hybrid with a 7-day mortality of 43.8%, which was not significantly different compared to the mortalities observed on the 3 non-Bt corn hybrids. However, unlike the performance of the PR population observed in the first trial, larvae of Cry1F-RR survived well on the other 3 pyramided Bt corn hybrids. The 7-day mortality of Cry1F-RR was only 34.4% on SmartStax[TM], which was not significantly different than the mortalities observed on the 3 non-Bt corn hybrids. The mortality (49.2%) of Cry1F-RR on VT Double Pro[TM] was also not significantly different compared to those values recorded on the non-Bt corn leaf tissue. Mortality (67.2%) of Cry1F-RR on the VT Triple Pro[TM] hybrid was significantly greater (P < 0.005) than the mortality on non-Bt corn leaf tissue but significantly less (P < 0.001) than that of FL and Cry1F-RS populations on Bt corn hybrids.

Dominance Level of Cry1F Resistance in S. frugiperda

Dominance level "D" measured using Stone's method (Stone 1968) based on the [LC.sub.50] values of FL, Cry1F-RR, and Cry1F-RS populations was < -0.37, suggesting that Cry1F resistance in Cry1F-RR was recessive or incompletely recessive (Table 3). Because all 3 populations could not survive on leaf tissue of the Viptera[TM] 3111 hybrid or N78N-3111 in both trials, effective dominance level, [D.sub.ML] , couldn't been calculated for this Bt corn product. [D.sub.ML] values measured based on larval mortality on leaf tissue of the other 6 Bt corn hybrids were consistent in the 2 trials, ranging from 0 to 0.33 in trial # 1 and from 0 to 0.22 in trial # 2. The results suggested that the Cry1F resistance in S. frugiperda was functionally recessive to incompletely recessive on leaf tissue of the 5 Bt corn hybrids representing 4 Bt corn traits, Herculex[R]I, Genuity[R]VT Double Pro[TM], Triple Pro[TM], and SmartStax[TM].

DISCUSSION

Since first being commercialized in 1996, Bt crops have gained an international attention and widely acceptance in the world, especially among corn and cotton producers in the United States (James 2011; NASS 2012). Cry1F expressed corn (event TC1507) was registered in 2001 in the United States to control above-ground lepidopteran pests including S. frugiperda. In 2003, Cry1F corn was first commercially cultivated in the United States and Puerto Rico to control S. frugiperda. This insect is the most important lepidopteran corn pest in Puerto Rico (US EPA 2007; Storer et al. 2012). Studies have revealed that field resistance to Cry1F corn in S. frugiperda occurred in late 2006 (US EPA 2007; Matten et al. 2008; Storer et al. 2010; Huang et al. 2011). In the current study, susceptibility of 2 field populations of S. frugiperda collected from Florida and Puerto Rico to purified Cry1F protein and corn leaf tissue of a commercial Cry1F corn hybrid was evaluated in the laboratory. Limited by the available amount of purified Bt protein, Cry1F susceptibility of S. frugiperda could be assayed up to only 100 [micro]g/g in this study. No significant larval mortality of the PR and Cry1F-RR populations was observed even at the highest Cry1F concentrations examined in the bioassays. The [LC.sub.50] values, therefore, could not be determined with the probit analysis for both populations (Table 2). Nevertheless, the results of this study clearly demonstrated that the population from Puerto Rico, compared to the Florida population, was highly resistant to both purified Cry1F protein and Cry1F corn leaf tissue. The Cry1F resistance was recessive or incompletely recessive as measured with both the Stone's dominance "D" value on Cry1F diet and the effective dominance level "[D.sub.ML]" on Cry1F corn leaf tissue. In the calculation of dominance, the FL population was considered homozygous susceptible with no resistance alleles. The resistance could be more recessive than that measured in this study if the assumption was not true. The dominance levels of the Cry1F resistance estimated in this study appeared to be similar as reported in another population of S. frugiperda collected from Puerto Rico in 2007 (Storer et al. 2010). It was reported that upon an initial confirmation of the field resistance to Cry1F corn in Puerto Rico, the technology providers immediately stopped the commercial sale of Cry1F corn seeds to growers in this area (Matten et al. 2008; Storer et al. 2010). Although limited by the insect sampling in the current study, our results suggest that the field resistance to Cry1F corn was persistent in Puerto Rico even after several yr without planting of Cry1F corn. A recent study also reported that field populations of S. frugiperda collected from 2 other locations in 2011 were still highly resistant to Cry1F protein in diet (Storer et al. 2012).

In both leaf tissue tests, all 5 populations of S. frugiperda could not survive for 7 days on the Agrisure[R] Viptera[TM] 3111 hybrid. The results suggested that Viptera[TM] 3111 Bt corn could completely overcome the Cry1F resistance and thus should provide a means for managing Cry1F resistance in this important target pest of Bt corn. In a previous study, survival of 14,400 neonates from 150 two-parental family lines of S. frugiperda collected from Florida and Louisiana was evaluated on Agrisure[R] Viptera[TM] 3111 plants using an [F.sub.2] screen (Yang et al. 2013). Results of that study showed that all larvae were killed within 7 days on Viptera[TM] 3111 corn leaf tissue. Although both the current and previous studies were not designed to evaluate the high dose assumption, the results of these studies suggest that Viptera[TM] 3111 corn is highly effective and likely produces a "high-dose" against S. frugiperda.

The Cry1F-susceptible population, FL, and the 2 F1 populations of 2 crosses, FL x PR and Cry1F-RS, were also susceptible to the other 3 pyramided Bt corn products: Genuity[R]VT Double Pro[TM], Triple Pro[TM], and SmartStax[TM]. The 7-day mortality on these Bt corn products was [greater than or equal to] 94.5% in both trials (Fig. 2). The results demonstrated that the Cry1F resistance in S. frugiperda was functionally recessive or nearly completely recessive on corn leaf tissue of the 3 pyramided Bt corn traits as showed in the [D.sub.ML] values in Table 3. However, performance of the Cry1F resistant populations (PR and Cry1F-RR) on corn leaf tissue of Genuity[R]VT Double Pro[TM], Triple Pro[TM], and SmartStax[TM] varied between the 2 trials. In the first trial, PR larvae appeared to be susceptible to the 3 pyramided Bt corn products with a 7-day mortality of 85.9-93.8% (Fig. 2). In contrast, larvae of the backcrossed and reselected population, Cry1F-RR, survived well on the 3 pyramided Bt corn products in the second trial with a 7-day mortality of only 34.4 to 67.2% (Fig. 2). The exact reasons causing the difference are unknown. One of the most likely reasons could be due to a result of the continued selections on Cry1F corn leaf tissue both before and after the backcross. For example, the original population (PR) collected from Puerto Rico might still not be homozygous for the Cry1F resistance and continued selection on Cry1F corn leaf tissue could eliminate the susceptible and probably heterozygous individuals in the population and thus could further elevate the resistance level in the Cry1F-RR population.

Additional studies are still needed to demonstrate if the Cry1F-RR population could survive on whole plants of these pyramided Bt corn products. Nevertheless, the results of the current study suggest that at least some levels of cross-resistance to the 3 pyramided Bt corn traits exist in Cry1F corn resistant S. frugiperda. Both VT Double Pro[TM] and Triple Pro[TM] contain Cry1A.105 and Cry2Ab2, while SmartStax[TM] expresses those proteins and Cry1F. Cry1A.105 is a chimeric gene comprised of domains I and II which are identical with the respective domains from Cry1Ab and Cry1Ac and domain III of Cry1F (Biosafety Clearing-House 2009). Thus it should not be surprising that some levels of cross-resistance could exist between Cry1F and Cry1A.105 because of the association in the gene structures of the 2 proteins. Studies have shown that S. frugiperda was somewhat tolerant to the single gene Cry1Ab corn hybrids (US EPA 2001b; Chilcutt et al. 2007; Hardke et al. 2011; Huang et al. 2011). In addition, Cry1Ac usually shares similar binding sites with Cry1Ab in the insect midgut membranes (Ballester et al. 1999; Ferre & Van Rie 2002; Hua et al. 2001; Tan 2010) and thus Cry1Ab resistance is often found to be cross-resistant to Cry1Ac in many insect species (Tabashnik et al. 1994; Ferre &Van Rie, 2002; Rang et al. 2004; Siqueira et al. 2004; Wu et al. 2009; Pereira et al. 2010; Tan 2010; Crespo et al. 2011; Zhang et al. 2013). Cry2Ab2 is a different protein compared to Cry1A and studies have shown that a Cry1A resistant insect is usually not cross-resistant to Cry2Ab2 (Wu et al. 2009; Brevault et al. 2009; Sivasupramaniam et al. 2008). Thus, the survival of the Cry1F-RR population on the 3 pyramided Bt corn products, Genuity[R]VT Double Pro[TM], VT Triple Pro[TM], and SmartStax[TM], could be due to a combination factor of cross-resistance and the expression level of Cry2Ab2 protein that may be not high enough by it alone to kill the Cry1F resistant larvae in a 7-day period of bioassays. The possible cross-resistance between single-gene and pyramided Bt corn in S. frugiperda suggest that careful selection of different Bt genes is essential in use of gene pyramiding strategy for resistance management.

Caption: Fig. 1. Larval mortality of Spodoptera frugiperda after 7 days on diet treated with different concentrations of purified Cry1F protein. Mean values across all treatments in each figure followed by the same letter are not significantly different (P < 0.05; LSMEANS test).

Caption: Fig. 2. Larval mortality of Spodoptera frugiperda after 7 days feeding on leaf tissue removed from non-Bt and Bt corn plants. Mean values across all treatments in each figure followed by the same letter are not significantly different (P < 0.05; LSMEANS test). NonBt-1in trial one = DKC 61-22, NonBt-1 in trial #2 = DKC 63-45, NonBt-2 in trial #1 = DKC 67-86, NonBt-2 in trial #2 = N78N-GT, NonBt-3 in trial #2 = Pioneer 31G66, HX1 = Pioneer 31D59, VT-2P in trial #1 =DKC 64-04, VT-2P in trial #2 = DKC 63-87, VT-3P in trial #1 =DKC 67-88 VT-3P in trial #2 = DKC 62-97, SmartStax = DKC 61-21, VIP = N78N-3111.

ENDNOTES

This article is published with the approval of the Director of the Louisiana Agricultural Experiment Station as manuscript No.2012-234-7661. This project represents work supported by the Louisiana Soybean and Feed Grain Promotion Board and USDA NC-205. This paper reports research results only. Mention of a proprietary product name does not constitute an endorsement for its use by Louisiana State University Agricultural Center and USDA-ARS.

REFERENCES CITED

ABBOTT, W. S. 1925. A method of computing the effectiveness of an insecticide. J. Econ. Entomol. 18: 265-267.

BALLESTER, V., GRANERO, F., TABASHNIK, B. E., MALVAR, T., AND FERRE, J. 1999. Integrative model for binding of Bacillus thuringiensis toxins in susceptible and resistant larvae of the diamondback moth (Plutella xylostella). Appl. Environ. Microbiol. 65:1413-1419.

BIOSAFETY CLEARING-HOUSE. 2009. Gene information, Cry1A.105. (http://bch.cbd.int/database/record. shtml?documentid=43771, Sep 2012).

BOURGUET, D., GENISSEL, A., AND RAYMOND, M. 2000. Insecticide resistance and dominance levels. J. Econ. Entomol. 93: 1588-1595.

BREVAULT, T., PRUDENT, P., VAISSAYRE, M., AND CARRIERE. Y. 2009. Susceptibility of Helicoverpa armigera (Lepidoptera: Noctuidae) to Cry1Ac and Cry2Ab2 insecticidal proteins in four countries of the West African cotton belt. J. Econ. Entomol. 102: 2301-9.

BUNTIN, G. D., LEE, R. D., WILSON, D. M., AND MCPHERSON, R. M. 2000. Evaluation of YieldGard transgenic resistance for control of fall armyworm and corn earworm (Lepidoptera: Noctuidae) on corn. Florida Entomol. 84: 37-42.

BUNTIN, G. D., ALL, J. N., LEE, R. D., AND WILSON, D. M. 2004. Plant-incorporated Bacillus thuringiensis resistance for control of fall armyworm and corn earworm (Lepidoptera: Noctuidae) in corn. J. Econ. Entomol. 97: 1603-1611.

BUNTIN, G. D. 2008. Corn expressing Cry1Ab or Cry1F endotoxin for fall armyworm and corn earworm (Lepidoptera: Noctuidae) management in field corn for grain production. Florida Entomol. 91: 523-530.

BURKNESS, E. C., DIVELY, G., PATTON, T., MOREY, A. C., AND HUTCHISON, W. D. 2010. Novel Vip3A Bacillus thuringiensis (Bt) maize approaches high-dose efficacy against Helicoverpa zea (Lepidoptera: Noctuidae) under field conditions. GM Crop 1:1-7.

CHILCUTT, C. F., ODVODY, G. N., CORREA, J. C., AND REMMERS, J. 2007. Effects of Bacillus thuringiensis transgenic corn on corn earworm and fall armyworm (Lepidoptera: Noctuidae) densities. J. Econ. Entomol. 100: 327-334.

CRESPO, A. L. B., RODRIGO-SIMON, A., SIQUEIRA, H. A. A., PEREIRA, E.J.G., FERRE, J., AND SIEGFRIED, B. D. 2011. Cross-resistance and mechanism of resistance to Cry1Ab toxin from Bacillus thuringiensis in a field-derived strain of European corn borer, Ostrinia nubilalis. J. Invertebr. Pathol. 107: 185-192.

DIFONZO, C., AND COLLEN, E. 2012. Handy Bt trait table. http://www3.ag.purdue.edu/agry/PCPP/Documents/Entry%20forms/Handy_Bt_Trait_Table .pdf, Sept. 2012].

FERRE, J., AND VAN RIE, J. 2002. Biochemistry and genetics of insect resistance to Bacillus thuringiensis. Ann. Rev. Entomol. 47: 501-533.

FINNEY, D. J. 1971. Probit analysis. Cambridge University Press, England.

GHIMIRE, M. N., HUANG, F., LEONARD, R. B., HEAD, G. P., AND YANG, Y. 2011. Susceptibility of Cry1Ab-susceptible And--resistant sugarcane borer to transgenic corn plants containing single or pyramided Bacillus thuringiensis genes. Crop Protect. 30:74-81.

HARDKE, J. T., LEONARD, B. R., HUANG, F., AND JACKSON, R. E. 2011. Damage and survivorship of fall armyworm (Lepidoptera: Noctuidae) on transgenic field corn expressing Bacillus thuringiensis Cry proteins. Crop Protect. 30: 168-172.

HUA, G., MASSON, L., JURAT-FUENTES, J. L., SCHWAB, G., AND ADANG, M. J. 2001. Binding analyses of Bacillus thuringiensis Cry delta-endotoxins using brush border membrane vesicles of Ostrinia nubilalis. Appl. Environ. Microbiol. 67: 872-879.

HUANG, F., LEONARD, B. R., AND WU, X. 2007. Resistance of sugarcane borer to Bacillus thuringiensis Cry1Ab toxin. Entomol. Exp. Appl. 124: 117-123.

HUANG, F., ANDOW, D. A., AND BUSCHMAN, L. L. 2011. Success of the high-dose/refuge resistance management strategy after 15 years of Bt crop use in North America. Entom. Exp. App. 140: 1-16.

JAMES, C. 2011. Global status of commercialized biotech/GM crops: 2011. ISAAA Brief No. 43. ISAAA: Ithaca, NY, USA.

MASSON, L., ERLANDSON, M., PUSZTAI-CAREY, M., BROUSSEAU, R., JUAREZ-PEREZ, V., AND FRUTOS, R. 1998. A holistic approach for determining the entomopathogenic potential of Bacillus thuringiensis strains. Appl. Environ. Microbiol. 64: 4782-4788.

MATTEN, S. R., HEAD, G. P., AND MACINTOSH, S. C. 2008. How government regulation can help or hinder the integration of Bt crops within IPM programs. In J. Romeis, A. M. Shelton, G. G. Kennedy (eds.), Integration of Insect Resistant Genetically Modified Crops with IPM Programs. Springer Science J> Business Media B. V., New York, USA, pp. 27-39.

MONSANTO. 2012. IRM grower guide: insect resistance management for U.S. corn and cotton-growing areas. (http://www.monsanto.com/products/Pages/insectresistance-management.aspx, Sep 2012).

NASS (NATIONAL AGRICULTURAL STATISTICS SERVICE). 2012. Acreage. USDA, Washington, DC. (http://usda. mannlib.cornell.edu/MannUsda/viewDocumentInfo. do?documentID=1000, Sep 2012).

PASHLEY, D. P. 1986. Host associated genetic differentiation in fall armyworm (Lepidoptera: Noctuidae): a sibling species complex. Ann. Entomol. Soc. Am. 79: 898-904.

PASHLEY, D. P., JOHNSON, S. J., AND SPARKS, A. N. 1985. Genetic population structure of migratory moths: the fall armyworm (Lepidoptera: Noctuidae). Ann. Entomol. Soc. Am. 78: 756-762.

PEREIRA, E. J. G., SIQUEIRA, H. A. A., ZHUANG, M., STONER, N. P., AND SIEGFRIED, B. D. 2010. Measurements of Cry1F binding and activity of luminal gut proteases in susceptible and Cry1F resistant Ostrinia nubilalis larvae (Lepidoptera: Crambidae). J. Invertebr. Pathol. 103: 1-7.

PUSZTAI-CAREY, M., CAREY, P., LESSARD, T., AND YAGUCHI, M. 1995. Isolation, quantification and purification of insecticidal proteins from endotoxins of Bacillus thuringiensis. US Patent No.5356788.

RANG, C., BERGVINGSON, D., BOHOROVA, N., HOISINGTON, D., AND FRUTOS, R. 2004. Competition of Bacillus thuringiensis Cry1 toxins for midgut binding sites: a basis for the development and management of transgenic tropical maize resistant to several stemborers. Curr. Microbiol. 49: 22-27.

SAS INSTITUTE Inc. 2010. SAS/STAT: 9.3 User's Third Edition SAS Institute Inc, Cary, NC.

SIEBERT, M. W., TINDALL, K. V., LEONARD, B. R., VAN DUYN, J. W., AND BABCOCK, J. M. 2008. Evaluation of corn hybrids expressing Cry1F (Herculex[R]I insect protection) against fall armyworm (Lepidoptera: Noctuidae) in the southern United States. J. Entomol. Sci. 43: 41-51.

SIQUERIA, H. A. A., MOELLENBECK, D. J., SPENCER, T. A., AND SIEGFRIED, B. D. 2004. Cross-resistance of Cry1Ab-selected Ostrinia nubilalis (Lepidoptera: Crambidae) to Bacillus thuringiensis [delta]-endotoxins. J. Econ. Entomol. 97:1049-1057.

SIVASUPRAMANIAM, S., MOAR, W. J., RUSCHKE, L. G., OSBORN, J. A., JIANG, C., SEBAUGH, J. L., BROWN, G. R., SHAPPLEY, Z. W., OPPENHUIZEN, M. E., MULLINS, J. W., AND GREENPLATE, J. T. 2008. Toxicity and characterization of cotton expressing Bacillus thuringiensis Cry1Ac and Cry2Ab2 proteins for control of lepidopteran pests. J. Econ. Entomol. 101: 546-54.

STONE, B. F. 1968. A formula for determining degree of dominance in cases of monofactorial inheritance of resistance to chemicals. W. H. O. Bull. 38: 325-326.

STORER, N. P., BABCOCK, J. M., SCHLENZ, M., MEADE, T., THOMPSON, G. D., BING, J. W., AND HUCKABA, R. M. 2010. Discovery and characterization of field resistance to Bt maize: Spodoptera frugiperda (Lepidoptera: Noctuidae) in Puerto Rico. J. Econ. Ento mol. 103: 1031-1038.

STORER, N. P., KUBISZAK, M. E., KING, J. E., THOMPSON, G. D., AND SANTOS, A. C. 2012. Status of resistance to Bt maize in Spodoptera frugiperda: Lessons from Puerto Rico. J. Invert. Pathol. 110: 294-300.

SYNGENTA. 2012. Corn trait Information: Agrisure Viptera[TM] 3111. (http://www.syngenta.com/country/us/ en/Seeds/Traits/CornTraits/Pages/content_authoring_Agrisurevip3111.aspx, Sep 2012).

TABASHNIK, B. E., FINSON, N., JOHNSON, M. W., AND HECKEL, D. G. 1994. Cross-resistance to Bacillus thuringiensis toxin Cry1F in the diamondback moth. Appl. Environ. Microbiol. 60: 4627-4629.

TAN, S. Y. 2010. Comparative susceptibility and binding of Cry1 Bacillus thuringiensis toxins to the Asian (Ostrinia furnacalis Guenee) and European (Ostrinia nubilalis Hubner) corn borers (Lepidoptera: Crambidae). PhD Dissertation. University of Nebraska, 161 pp.

US EPA (UNITED STATES ENVIRONMENTAL PROTECTION AGENCY). 2001a. Biopesticide registration action document: Bacillus thuringiensis Cry1F Corn. (bch.cbd.int/database/attachment/?id=10711, Sep 2012).

US EPA (UNITED STATES ENVIRONMENTAL PROTECTION AGENCY). 2001b. Biopesticide registration action document: Bacillus thuringiensis plant-incorporated protectants. (http://www.epa.gov/oppbppd1/ biopesticides/pips/bt_brad.htm, Apr 2012).

US EPA (UNITED STATES ENVIRONMENTAL PROTECTION AGENCY). 2007. Review of Dow AgroScience's (and Pioneer HiBred's) submission (dated July 12, 2007) regarding fall armyworm resistance to the Cry1F protein expressed in TC1507 Herculex[R] I insect protection maize in Puerto Rico (EPA registrations 68467-2 and 29964-3). DP Barcode: 342635. Decision: 381550. MRID#: 471760-01. US EPA, Washington, DC, USA.

US EPA (UNITED STATES ENVIRONMENTAL PROTECTION AGENCY). 2009. Biopesticide registration action document: Bacillus thuringiensis Vip3Aa20 insecticidal protein and the genetic material necessary for its production (via elements of vector pNOV1300) in event MIR162 maize (OECD unique identifier: SYN-IR162-4). (http://cera-gmc.org/docs/ decdocs/09-131-023.pdf, Sep 2012)

US EPA (UNITED STATES ENVIRONMENTAL PROTECTION AGENCY). 2010. Biopesticide registration action document: Bacillus thuringiensis Cry1A.105 and Cry2Ab2 insecticidal proteins and the genetic material necessary for their production in corn. (http://www. epa.gov/oppbppd1/biopesticides/pips/mon-89034 brad.pdf, Sep 2012].

WU, X., LEONARD, B. R., ZHU, Y. C., ABEL, C. A., HEAD, G. P., AND HUANG, F. 2009. Susceptibility of Cry1Ab-resistant and -susceptible sugarcane borer (Lepidoptera: Crambidae) to four Bacillus thuringiensis toxins. J. Invertbr. Pathol. 100: 29-34.

YANG, F., HUANG, F., QURESHI, J. A., LEONARD, B. R., NIU, Y., ZHANG L., AND WANGILA, D. S. 2013. Susceptibility of Louisiana and Florida populations of Spodoptera frugiperda (Lepidoptera: Noctuidae) to transgenic Agrisure[R]Viptera[TM] 3111 maize. Crop Protection. 50: 37-39.

ZHANG, L., HUANG, F., LEONARD, B. R., ZHU, Y., WANGILA, D. S., YANG, F., AND NIU, Y. 2013. Susceptibility of Cry1Ab maize-resistant and -susceptible strains of sugarcane borer (Lepidoptera: Crambidae) to four Individual Cry Proteins. J. Inverteb. Path. 112: 267-272.

YING NIU (1), ROBERT L. MEAGHER JR (2), FEI YANG (1) AND FANGNENG HUANG (1) *

(1) Department of Entomology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803-1710, USA

(2) Insect Behavior and Biocontrol Unit, CMAVE USDA-ARS, Gainesville, FL 32608, USA

* Corresponding author; E-mail: fhuang@agcenter.lsu.edu

TABLE 1. HYBRIDS USED IN EVALUATION OF SUSCEPTIBILITY OF SPODOPTERA
FRUGIPERDA TO BT CORN.

Traits               Corn hybrid              Event

Non-Bt               DKC 61-22                  --
Non-Bt               DKC 67-86                  --
Non-Bt               DKC 63-45                  --
Non-Bt               N78N-GT                    --
Non-Bt               Pioneer 31G66              --

Herculex[R]I         Pioneer 31D59   TC1507
Genuity[R]VT         DKC 64-04       MON89034
  Double Pro[TM]     DKC 63-87       MON89034
Genuity[R]VT         DKC 67-88       MON89034+ MON 88017
  Triple Pro[TM]
                     DKC 62-97       MON89034+ MON 86017

Genuity[R]VT         DKC 61-21       MON89034+ MON88017+TC1507+
  SmartStax[R]                       DAS-59122
Agrisure[R]          N78N-3111       MIR162+Bt11+MIR604
  Viptera[TM] 3111

Traits               Used in       Abbreviation
                                   in the figures

Non-Bt               Trial 1         NonBt-1
Non-Bt               Trial 1         NonBt-2
Non-Bt               Trial 2         NonBt-1
Non-Bt               Trial 2         NonBt-2
Non-Bt               Trial 2         NonBt-3

Herculex[R]I         Trial 1 & 2     HX1
Genuity[R]VT         Trial 1         VT-2P
  Double Pro[TM]     Trial 2         VT-2P
Genuity[R]VT         Trial 1         VT-3P
  Triple Pro[TM]
                     Trial 2         VT-3P

Genuity[R]VT         Trial 1 & 2     SmartStax
  SmartStax[R]
Agrisure[R]          Trial 1 & 2     VIP
  Viptera[TM] 3111

Traits                           Bt genes                Major target
                                                             pests

Non-Bt               closely related to DKC 61-21             --
Non-Bt               closely related to DKC 67-88             --
Non-Bt               closely related to DKC 61-21             --
Non-Bt               closely related to N78N-3111             --
Non-Bt               closely related to Pioneer 31D59         --

Herculex[R]I         Cry1F                               lepidoptera
Genuity[R]VT         Cry1A.105, Cry2Ab2                  lepidoptera
  Double Pro[TM]     Cry1A.105, Cry2Ab2                  lepidoptera
Genuity[R]VT         Cry1A.105, Cry2Ab2, Cry3Bb1         lepidoptera &
  Triple Pro[TM]                                         rootworms
                     Cry1A.105, Cry2Ab2, Cry3Bb1         lepidoptera &
                                                         rootworms
Genuity[R]VT         Cry1A.105, Cry2Ab, Cry1F,           lepidoptera &
  SmartStax[R]       Cry3Bb1, Cry34/35Ab                 rootworms
Agrisure[R]          Vip3A,Cry1Ab,mCry3A                 lepidoptera &
  Viptera[TM] 3111                                       rootworms

TABLE 2. [LC.sub.50s] AND 95% CONFIDENCE INTERVALS (CI) BASED ON
LARVAL MORTALITY OF SPODOPTERA FRUGIPERDA NEONATES ON DIET TREATED
WITH PURIFIED CRY1F BACILLUS THURINGIENSIS PROTEIN. *

Population   N #   Slope [+ or -] SE    [LC.sub.50](95%CI)
                                          ([micro]g/g)

                                     Trial 1

FL           503   1.13 [+ or -] 0.18    0.23(0.11-0.37)
PR                         --                 >31.6

                                     Trial 2

FL           553   1.38 [+ or -] 0.22    0.13(0.07-0.20)
Cry1F-RS     675   1.47 [+ or -] 0.16    1.07(0.76-1.50)
Cry1F-RR                   --                 >100

Population   [chi square]   df   Resistance
                                   ratio

                            Trial 1

FL              45.87       18       --
PR                --        --      >137

                            Trial 2

FL              71.62       18       --
Cry1F-RS        64.08       22      8.2
Cry1F-RR          --        --      >769

# Total number of neonates assayed.

([dagger]) Resistance ratio of an insect population was calculated
by dividing the [LC.sub.50] value of the population by that of the
FL population.

TABLE 3. DOMINANCE LEVEL OF CRY1F RESISTANCE IN
SPODOPTERA FRUGIPERDA COMPUTED USING
DATA FROM DIET INCORPORATING AND LEAF
TISSUE BIOASSAYS.

                                       Dominance
Test material and trial                 level *

Stone's dominance "D" value

Diet incorporating, trial-2              -0.37

Effective dominance "[D.sub.ML]"

Pioneer 31D59, leaf tissue-trial 1       0.23
DKC 64-04, leaf tissue, trial-1          0.19
DKC 67-88, leaf tissue, trial-1          0.33
DKC 61-21, leaf tissue, trial-1          0.00
N78N-3111, leaf tissue, trial-1           --

Pioneer 31D59, leaf tissue, trial-2      0.12
DKC 63-87, leaf tissue, trial-2          0.08
DKC 62-97, leaf tissue, trial-2          0.00
DKC 61-21, leaf tissue, trial-2          0.00
N78N-3111, leaf tissue, trial-2           --

* Stone's dominance "D" value ranges from -1 to 1: a value of -1
indicates resistance is completely recessive; a value of 0 suggests
resistance is addictive; and a value of 1 implies resistance is
completely dominant. Effective dominance "[D.sub.ML]" ranges
between 0 and 1. [D.sub.ML] = 0 refers to a completely recessive
resistance and [D.sub.ML] = 1 means the resistance is completely
dominant.


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