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Green leaf chemistry of various turfgrasses: differentiation and resistance to fall armyworm. (Turfgrass Science).

TURFGRASSES are very important to society in the SA and worldwide. They continue to increase the quality of our lives and environment at home, work, and recreation sites. Understanding the leaf chemistry of specific grasses could ultimately help us develop grasses with better agronomic qualities with insect and disease resistance.

Reinert (1982) and Quisenberry (1990) reviewed the potential of turfgrass host plant resistance to insects and mites. Very little is known about turfgrass leaf chemistry and its relationship to insect pests, and most insect studies have dealt with sources of insect resistance to specific insect pests such as chinch bugs, billbugs, sod webworms, mealybugs, mole crickets, and FAWs (Vittum et al., 1999), and not mechanisms of resistance.

The FAW is a major pest of turfgrass in the southeastern USA (Vittum et al., 1999; Potter, 1998). Wiseman and Davis (1979) and Wiseman et al. (1982) demonstrated antibiosis and nonpreference resistance to the FAW in common centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. Reinert et al. (1997) reported a number of zoysiagrass [Zoysia matrella (L.) Merr.] genotypes and cultivars that were resistant to the FAW. Chang et al. (1985a, 1985b, 1986) showed the effects of centipedegrass on FAW behavior, growth, and development. They also found that N fertilization affected FAW preference for centipedegrass.

The ability of flavonoids and polyphenols to impart resistance in plant hosts to insect pests (Waiss et al., 1979; Hedin and Waage, 1986; Lindroth and Peterson, 1988; Snook et al., 1994, 1995; Wiseman et al., 1996) is well known. Gueldner et al. (1991) postulated that the antibiosis factors in fresh centipedegrass were plant polyphenols. Wiseman et al. (1990) stated that chlorogenic acid and other luteolin compounds such as maysin were the major factors responsible for the antibiotic resistance to FAW larvae. There is still a limited amount of information available on the flavonoids and polyphenols in turfgrass and the effects of these compounds on insect resistance. Our previous work documented that the FAW was susceptible to growth inhibition when exposed to the flavonoid maysin (a luteolin-C-glycoside) in laboratory bioassays (Snook et al., 1997). This prompted us to examine the types and levels of polyphenols and flavonoids of a number of turfgrasses with different levels of resistance to the FAW.

MATERIALS AND METHODS

Plant Material

Grass species representing a wide range of grasses commonly used in commercial and home turf and lawn applications were maintained in field plots at the Pee Dee Research and Education Center, Florence, SC, using standard cultural and fertilization practices. Turfgrasses evaluated in this study included four warm season grasses: Emerald zoysiagrass, `Tifway' and Tifgreen bermudagrass [Cynodon dactylon (L.)

Pers. x C. transvaalensis Burtt Davy], common centipedegrass, and Raleigh St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze]; and two cool season grasses: `Kentucky 31' tall fescue (Festuca arundinacea Schreb.), and Kenblue Kentucky bluegrass (Poa pratensis L.).

In April 1998 and 1999, 0.25 g of leaf material was removed from each grass entry in the field and cut into small pieces ([approximately equal to] 3-mm long) and placed in a scintillation vial with 10 mL of methanol (teflon-lined cap utilized). Three replicates of each grass type were prepared. The samples were stored at -20[degrees]C until analysis.

High-Performance Liquid Chromatography Analysis

The aforementioned turfgrasses were analyzed for their polyphenol and flavonoid profiles by high performance liquid chromatography-diode array spectral characterization. Prior to analysis, 50 [micro]L of a methanolic chrysin solution (chrysin recrystallized from amyl alcohol; 0.08 mg 50 [micro][L.sup.-1]) was added as an internal standard. After grinding the plant material with a polytron (Brinkmann Instruments, Inc., Westbury, NY), solutions were filtered and aliquots analyzed by reversed-phase high-performance liquid chromatography (HPLC) using a MeOH:[H.sub.2]O linear gradient from 10% to 100% MeOH in 35 min, a flow rate of 1 mL [min.sup.-1], and detection at 340 nm. Each solvent contained 0.1% [H.sub.3]P[O.sub.4]. Analyses were performed with an Altex Ultrasphere C18, 5-[micro]m column (4.6 by 250 mm, Beckman Instruments, Norcross, GA) using a Hewlett-Packard 1050 diode array HPLC. Quantitation was performed with chrysin's response factor.

Isolation of Flavone Glycosides

Extraction

Methanol extracts were filtered, concentrated by rotary evaporation to [approximately equal to] 100 mL, and 25 mL of water added. The solution was further concentrated until only an aqueous solution remained, and then extracted with C[H.sub.2][Cl.sub.2]. The aqueous portion contained the compounds of interest.

Isolation

Isolation was mainly by preparative reversed-phase column chromatography on Waters Bondapak C18 bulk packing material (Millipore Corp., Milford, MA) which was packed into a glass chromatography column (54 x 2.54 cm, 1.05 kg [cm.sup.-2] N pressure used to aid flow), washed with MeOH and recycled to [H.sub.2]O. The water solution of the flavonoids was chromatographed on this column. Salts were eluted with water and the compounds of interest eluted with various percentages of MeOH:[H.sub.2]O (v/v). Most of the flavonoids eluted from the column with 30 to 60% MeOH:[H.sub.2]O. Additional separation of the flavonoids was accomplished by submitting individual fractions again to reversed-phase chromatography on a Cheminert LC column (108 by 1.25 cm, Valco Instruments Co., Inc., Houston, TX), packed with the Waters Bondapak 500 C18 material, loop injection valve, using the following linear solvent program: 40 to 60% MeOH:[H.sub.2]O in 400 min; 8-mL fractions were collected; column effluent monitored by HPLC.

Identification

Preliminary identifications of polyphenols and flavonoids were by UV spectra and retention time (RT) correlations with standards. Also, some isolated flavonoids were hydrolyzed with 0.1 M HCI at 100[degrees]C for 30, 60, and 120 min, and the liberated products analyzed by HPLC or GC (for sugars as their silylated derivatives). Selected compounds were submitted to fast atom bombardment (FAB)--mass spectrometry (MS) analyses in a glycerol matrix.

Bioassay Procedures

Bioassay of Grasses for Fall Armyworm Resistance

Samples of zoysiagrass, bermudagrass, centipedegrass, and St. Augustinegrass were collected from field plots and taken to the laboratory for evaluation. Tall fescue and Kentucky bluegrass samples were not available for FAW larval bioassays. Grass clippings were placed in petri dishes (15-cm diam. by 1.5-cm deep) on moistened filter paper, and each dish was infested with five 3- to 4-d-old FAW larvae. Fresh grass clippings were added to each dish every two days, and the filter paper was moistened as needed. Petri dishes were arranged in a randomized block design with four replications. Each replicate consisted of two petri dishes, and 40 FAW larvae were evaluated for each grass. The larvae were allowed to feed for 7 d, and surviving larvae were counted and weighed at 2 and 7 d after infestation to determine larval weight and survival.

Data for larval survival and weight were analyzed by ANOVA. Treatment means were separated by Duncan's new multiple range test, P = 0.05 (SAS Institute, 1996).

Bioassay of Individual Compounds

Chlorogenic acid and selected flavonoids were deposited onto celufil (U.S. Biochemical, Cleveland, OH) for bioassay studies (Snook et al., 1995). Into a 500-mL round bottom flask, 5 g of celufil was added and the desired compound added as a MeOH solution (100 mL). The solvent was evaporated to deposit the compound onto the celufil. Concentrations for each compound were 480, 240, 120, 60, and 30 mg 2 [g.sup.-1] celufil. Each compound and celufil mixture was added to 25 g of diluted pinto bean diet (Perkins, 1979; Snook et al., 1995) giving a final concentration of 17.76, 8.88, 4.44, 2.22, and 1.11 mg [g.sup.-1], respectively. These concentrations fall within the range of turfgrass samples. Detached, disposable plastic pipette bulbs were filled with 2 g of the diet and celufil mixture, allowed to solidify, and one neonate FAW was placed on the diet. The bulbs were placed in diet cups and larval weights measured after 8 d. Ten replications for each compound concentration were used. Not all compounds were tested at the highest or lowest concentrations.

Data for chlorogenic acid, flavonoids, and total polyphenols were analyzed by ANOVA. Treatment means were separated by Duncan's Multiple Range Test, P = 0.05 (SAS Institute, 1996).

RESULTS AND DISCUSSION

High-Performance Liquid Chromatography Analysis

When the turfgrass species were analyzed for their polyphenol and flavonoid profiles by high performance liquid chromatography-diode array spectral characterization, each grass species yielded a unique profile that allowed it to be differentiated from the other grasses (Fig. 1). These studies also indicate that grass leaf chemistry could be used as an additional tool to differentiate among and identify specific grass species. Leaf chemistry may differentiate grass species and certain cultivars that could not be differentiated from morphological characteristics. Our studies have already confirmed that it is possible to determine specific grass types and possible grass contamination from green leaf chemistry, and additional studies to expand this diagnostic ability are merited.

[FIGURE 1 OMITTED]

Zoysiagrass

Emerald zoysiagrass is characterized by the presence of chlorogenic acid and a group of >15 flavonoids that gave UV spectra, indicating all were luteolin-glycosides (see structures in Fig. 2). Major constituents in zoysiagrass were luteolin-glucosylarabinoside, luteolin-diarabinoside, and methoxy-luteolin-diarabinoside, as determined by UV, hydrolysis, and MS.

[FIGURE 2 OMITTED]

Bermudagrass

Tifgreen bermudagrass also exhibited a pattern of flavonoid-glycosides, but contained no chlorogenic acid. Further, UV spectral studies indicated at least two of the flavonoids in bermudagrass were apigenin-glycosides in addition to several luteolin-glycosides. Several compounds were isolated and characterized by UV, acid hydrolysis, and FAB-MS. The compound with RT = 15.0 min had a luteolin UV spectra, yielded no sugars on acid hydrolysis, and had a molecular weight (MW) of 580, indicating it was a di-C-glycoside (luteolin-glucoside-arabinoside) with the sugars occupying the sixth and eighth positions. The compound at RT = 16.1 min had an apigenin UV spectra, yielded only glucose on acid hydrolysis, and had a MW of 564, indicating it was apigenin-C-arabinosyl-O-glucoside. The compound at RT = 17.0 min had a luteolin UV spectra, yielded only glucose on hydrolysis, and had a MW of 594, indicating it was methoxy-luteolin-C-arabinosyl-O-glucoside. The compound at RT = 18.2 min had an apigenin UV spectra, liberated glucose on hydrolysis, and has tentatively been identified as apigenin-C-arabinosyl-O-glucoside.

Centipedegrass and Tall Fescue

Common centipedegrass and Ky 31 tall fescue HPLC profiles were of a similar nature in that both contain high levels of chlorogenic acid, but their flavonoid composition was greatly different. Centipedegrass has been shown to contain maysin, an unusual luteolin-diglycoside that possesses a unique keto-sugar (Wiseman et al., 1990). Centipedegrass has luteolin-type flavonoid-glycosides, while UV spectra indicated tall fescue grass contains quercetin-type flavonoids. The compound in fescue eluting at RT = 19.5 min was isolated as described above and on acid hydrolysis yielded rhamnose, glucose, rutinose, and quercetin as determined by GC and HPLC co-elution with authentic standards indicating the compound as rutin. Co-elution with rutin further confirmed the identification.

Kentucky Bluegrass and St. Augustinegrass

Kenblue Kentucky bluegrass and Raleigh St. Augustinegrass gave HPLC profiles much different from the other grass types analyzed in this study. Bluegrass and St. Augustinegrass contained no chlorogenic acid. These grasses contained several luteolin-glycosides but not the broad, multiple flavonoid profile of zoysia and bermuda grasses. The large peak at RT = 19.5 min of St. Augustinegrass actually is composed of four components. Hydrolysis studies of this group as a whole and the group of compounds at RT = 21.2 min showed that arabinose and glucose were liberated during hydrolysis, with both groups giving rise to one compound (Compd. 1). Also, the compounds at RT = 21.2 min liberated ferulic and sinapinic acids. Prolonged heating (18 h) of Compd. 1 with 0.1 M HCl at 100[degrees]C yielded a mixture of Compd. 1 and a second compound. It is postulated that Compd. 1 probably was an 8-C-glycosylluteolin, as isomerization of 6- and 8-C-glycosides by acid is well known (Chopin and Bouillant, 1975; Harborne and Williams, 2000). Preliminary FAB-MS studies of the compounds at RT = 19.5 min gave a molecular ion of 622, indicating the compounds are either dimethoxyluteolin-arabinosyl-ferulate and/or 4'-methoxy-apigenin-glucosyl-ferulate. The peak at RT = 21.2 min in St. Augustinegrass gave FAB-MS ions at 798 and 822. Besides the sugars listed above, hydrolysis liberated ferulic and sinapinic acids. Postulated structures are dimethoxy-luteolin-arabinosyl-ferulate-sinapinate and/or dimethoxy-luteolin-glucosyl-diferulate (MW = 828) and dimethoxy-luteolin-arabinosyl-ferulate (MW = 798).

Preliminary analysis of the flavonoids of Kentucky bluegrass indicates the compound at RT = 16.8 min to have a luteolin UV spectra. The compound at RT = 18.4 min was unusual in that it required acetic acid in methanol to elute from a silicic acid column. Common flavone-glycosides will elute from this system with much less polar solvents. Hydrolysis studies showed only glucose was liberated. Preliminary FAB-MS gave only an ion of mass 498. The compound has a typical flavone-flavonol UV spectra (lambda max 250, 270, 355 nm) but no structure can be assigned at this time. Further characterization is needed.

Structure and Antibiosis Relationships Model Compound Bioassay Studies

Chlorogenic acid, luteolin, and the flavonoid-glycosides rutin, maysin, and isoorientin were submitted to a laboratory bioassay against the FAW. These compounds represented the major types of polyphenols found in the turfgrasses studied (Fig. 2). All were highly active in reducing larval weights at 5 to 10 mM concentration (Fig. 3). Since the aglycone luteolin was of similar activity to the glycosylated-luteolins maysin and isoorientin, the nature of the sugar residue appears relatively unimportant for antibiosis activity. The high activity of rutin and chlorogenic acid showed that the activity depended on the presence of an ortho-dihydroxy phenyl group. Elliger et al. (1980) demonstrated the importance of orthodihydroxyl groups in corn earworm antibiosis. Removal of one of the hydroxyls or blockage by methylation halved the activity of the resulting compounds towards corn earworm (Snook et al., 1994).

[FIGURES 2-3 OMITTED]

Turfgrass Bioassay Studies for Fall Armyworm Resistance

Fall armyworm growth was affected by the four grass species evaluated in this study (Table 1). Larval survival was not significantly different in this test. The presence of multiple larvae in each dish and cannibalism made it very difficult to detect differences in survival. However, significant differences in larval weight were apparent 2 d (F = 295.263; df = 4, 12; P = 0.0001) and 7 d (F = 42.943; df = 4, 12; P = 0.0001) after the larvae were placed on the various grass species. In this study, FAW larvae survived and gained significant weight on St. Augustinegrass compared with zoysiagrass and centipedegrass, even though the weights were significantly less for FAW larvae that fed on bermudagrass. Centipedegrass exhibited relatively high levels of resistance to FAW; however, certain cultivars of zoysiagrass other than Emerald were more resistant (unpublished data). Zoysiagrass has a moderate to high level of resistance to FAW, and it appears to be as resistant as centipedegrass, if not more so. Larval growth reductions 7 d after infestation (as a percentage of the bermudagrasses) were 90, 79, and 29% for Emerald zoysiagrass, common centipedegrass, and Raleigh St. Augustinegrass, respectively. The order of suitability for FAW feeding in this study was bermudagrass > St. Augustinegrass > centipedegrass > zoysiagrass.

Levels of Polyphenols and Flavonoids in Turfgrasses

Levels of chlorogenic acid, flavonoids, and total phenolics in the turfgrasses studied are presented in Table 2. There were significant differences in the levels of chlorogenic acid (F = 143.51; df = 5, 10; P = 0.0001), flavonoids (F = 54.87; df = 5, 10; P = 0.0001), and total polyphenols (F = 53.57; df = 5,10; P = 0.0001) found in the various turfgrasses. Total polyphenols were higher in St. Augustinegrass and centipedegrass than in zoysiagrass, but zoysiagrass-fed FAW had lower larval weights. Centipedegrass also contained very high levels of chlorogenic acid (0.52% fresh weight), which was five to 10 times higher than those found in zoysiagrass or tall fescue. This high level of chlorogenic acid, together with appreciable amounts of maysin, is thought to be important in centipedegrass toxicity to FAW (Wiseman et al., 1990). However, chlorogenic acid was higher in centipedegrass than zoysiagrass, but both grasses were highly toxic to FAW. This would indicate that other chemical compounds are probably involved in zoysiagrass, or the types of luteolins found in zoysiagrass may be more toxic to FAW. St. Augustinegrass had the highest flavonoid levels in this study, but it was only moderately toxic to FAW. This would indicate that the flavonoids or luteolins found in St. Augustinegrass are not very toxic to FAW larvae. The preliminary indication that these flavonoids are highly methoxylated supports this as noted above by Elliger et al. (1980) and Snook et al. (1994). The laboratory bioassays show that the luteolin aglycone is just as active as the glycosides; therefore, the nature of the sugar moiety is not important for activity. However, the activity of the aglycone in an artificial diet may be different from the more soluble glycosides that occur in the grass leaves.

Total flavonoids and total polyphenols from the different grass species could not be correlated with reduced weight gains of FAW larvae in this study. Individual flavonoids and polyphenols will have to be determined and quantified for each grass species before correlations can be made for FAW resistance in specific turfgrasses.

Abbreviations: Compd. 1, Compound 1; FAB, fast atom bombardment; FAW, fall armyworm; HPLC, high-performance liquid chromatography; MS, mass spectrometry; MW, molecular weight; RT, retention time.
Table 1. Fall Armyworm survival and weight on different warm season
turfgrasses.

                               Larval survival after days of feeding

Turfgrass                              2 d                   7 d

                                                  %

`Emerald' zoysiagrass          80 [+ or -] 7.07a     30 [+ or -] 4.08a
                                ([dagger])
Common centipedegrass          88 [+ or -] 4.79a     48 [+ or -] 2.50a
`Raleigh' St. Augustinegrass   88 [+ or -] 4.79a     48 [+ or -] 4.79a
`Tifgreen' bermudagrass        85 [+ or -] 6.45a     40 [+ or -] 9.13a
`Tifway' bermudagrass          88 [+ or -] 2.50a     30 [+ or -] 5.77a

                                              Larval wt.

Turfgrass                              2 d                   7 d

                                                  mg

`Emerald' zoysiagrass          3.4 [+ or -] 0.14c   31.6 [+ or -] 5.89c
Common centipedegrass          5.0 [+ or -] 0.31c       72.8 [+ or -]
                                                          1.73c
`Raleigh' St. Augustinegrass   15.5 [+ or -] 0.50b     247.4 [+ or -]
                                                          6.70b
`Tifgreen' bermudagrass        31.4 [+ or -] 1.07a     334.0 [+ or -]
                                                          37.70a
`Tifway' bermudagrass          18.0 [+ or -] 1.19b     362.6 [+ or -]
                                                          32.57a

([dagger]) Means ([+ or -]SE) followed by the same letter in the same
column do not differ significantly by Duncan's new multiple range
test (P = 0.05).

Table 2. Levels of chlorogenic acid, flavonoids, and total polyphenols
in turfgrasses.

                                          Fresh weight

                          Chlorogenic        Total          Total
Turfgrass                     acid         flavonoids      phenolics

                                               %

`Emerald' zoysiagrass    0.063 [+ or -]  0.581 [+ or -]    0.644 [+
                            0.008b           0.071b      or -] 0.079b
                           ([dagger])
`Tifgreen' bermudagrass  0 [+ or -] 0c   0.354 [+ or -]    0.354 [+
                                             0.046c      or -] 0.046c
Common centipedegrass    0.520 [+ or -]  0.437 [+ or -]    0.957 [+
                             0.043a          0.043c      or -] 0.077a
`Kentucky 31' tall       0.109 [+ or -]  0.093 [+ or -]    0.202 [+
 rescue                      0.006b          0.004d      or -] 0.010c
`Kenblue' Kentucky       0 [+ or -] 0c   0.202 [+ or -]    0.202 [+
 bluegrass                                   0.011d      or -] 0.011c
`Raleigh' St.            0 [+ or -] 0c   1.035 [+ or -]    1.035 [+
 Augustinegrass                              0.051a      or -] 0.057a

([dagger]) Means ([+ or -]SE) followed by the same letter in the same
column do not differ significantly by Duncan's new multiple range
test (P = 0.05).


REFERENCES

Chang, N.T., B.R. Wiseman, R.E. Lynch, and D.H. Habeck. 1985a. Fall armyworm (Lepidoptera: Noctuidae) orientation and preference for selected grasses. Fla. Entomol. 68:296-303.

Chang, N.T., B.R. Wiseman, R.E. Lynch, and D.H. Habeck. 1985b. Influence of N fertilizer on the resistance of selected grasses to fall armyworm larvae. J. Agric. Entomol. 2:137-146.

Chang, N.T., B.R. Wiseman, R.E. Lynch, and D.H. Habeck. 1986. Growth and development of fall armyworm (Lepidoptera: Noctuidae) on selected grasses. Environ. Entomol. 15:182-189.

Chopin, J., and M.L. Bouillant. 1975. C-Glycosylflavonoids. p. 644. In J.B. Harborne et al. (ed.) The flavonoids. Academic Press, New York.

Elliger, C.A., B.G. Chan, and A.C. Waiss, Jr. 1980. Flavonoids as larval growth inhibitors. Naturwissenschaften 67:358-360.

Gueldner, R.C., M.E. Snook, B.R. Wiseman, N.W. Widstrom, D.S. Himmelsbach, and C.E. Costello. 1991. Maysin in corn, teosinte and centipede grass, p. 251. In P.A. Hedin (ed.) Naturally occurring pest bioregulators. ACS Symposium Series No. 449. Am. Chem. Soc., Washington, DC.

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Potter, D.A. 1998. Destructive turfgrass insects: Biology, diagnosis, and control. Ann Arbor Press, Chelsea, MI.

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Reinert, J.A. 1982. A review of host resistance in turfgrass to insects and acarines with emphasis on the southern chinch bug. p. 3-12. In H.D. Niemczyk and B.G. Joyner (ed.) Advances in turfgrass entomology. Hammer Graphics, Piqua, OH.

Reinert, J.A., M.C. Engelke, J.C. Reed, S.J. Maranz, and B.R. Wiseman. 1997. Susceptibility of cool and warm season turfgrasses to fall armyworm, Spodoptera frugiperda. Int. Turfgrass Soc. Res. J. 8:1003-1011.

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Snook, M.E., N.W. Widstrom, B.R. Wiseman, P.F. Byrne, J.S. Harwood, and C.E. Costello. 1995. New C-4'-hydroxy derivatives of maysin and 3'-methoxymaysin isolated from corn silks (Zea mays). J. Agric. Food Chem. 43:2740-2745.

Snook, M.E., N.W. Widstrom, B.R. Wiseman, R.C. Gueldner, R.L. Wilson, D.S. Himmelsbach, J.S. Harwood, and C.E. Costello. 1994. New flavone C-glycosides from (Zea mays L.) for the control of the corn earworm (Helicoverpa zea). p. 122. In P.A. Hedin (ed.) Bioregulators for crop protection and pest control. ACS Symposium Series No. 557. Am. Chem. Soc., Washington, DC.

Snook, M.E., B.R. Wiseman, N.W. Widstrom, and R.L. Wilson. 1997. Chemicals associated with maize resistance to corn earworm and fall armyworm, p. 37. In J.A. Mihm (ed.) Insect resistant maize: Recent advances and utilization. Proc. Int. Symp., Mexico, D.F. 27 Nov. to 3 Dec. 1994. CIMMYT, Mexico, D.F., Mexico.

Vittum, P.J., M.G. Villani, and H. Tashiro. 1999. Turfgrass Insects of the United States and Canada. Cornell Univ. Press, Ithaca, NY.

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Wiseman, B.R., M.E. Snook, and N.W. Widstrom. 1996. Feeding response of corn earworm larvae (Lepidoptera: Noctuidae) on corn silks of varying flavone content. J. Econ. Entomol. 89:1040-1044.

Albert W. Johnson, * Maurice E. Snook, and Billy R. Wiseman

A.W. Johnson, Dep. of Entomology, Clemson Univ., Pee Dee Research and Education Center, 2200 Pocket Rd., Florence, SC 29506; M.E. Snook, Russell Research Center, P.O. Box 5677, Athens, GA 30604; and Billy R. Wiseman, USDA-ARS (Retired), Insect Biology and Population Management Research Laboratory, P.O. Box 748, Tifton, GA 31793. Technical Contribution No. 4646 of the South Carolina Agric. Exp. Stn., Clemson Univ. Received 22 Nov. 2001.

* Corresponding author (ajhnsn@clemson.edu).
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