Roles of amino acids,protein, and fiber in leaf-feeding resistance of corn to the fall armyworm

The free amino acids have been shown by isolational work and choice bioassays to be more important than all other factors evaluated in defining leaf-feeding resistance of corn (Zea mays L.) to fall armyworm (FAW) [(Spodoptera frugiperda J.E. Smith)] larvae. 6-MBOA (6-methoxybenzoxazolinone) and maysin, toxins present in corn, were shown not to be significant factors for leaf-feeding resistance to first-instar FAW larvae because of their low concentrations in the whorl. Amino acid analysis showed that while the ratios of the essential amino acids in susceptible (S) and resistant (R) lines were similar, there were differences in the nonessential amino acids, particularly aspartic acid, which was higher in R lines. Also, the ratio of essential amino acids to nonessential amino acids was important, being too low in expressed whorl leaf juice (obtained from V₈–V₁₀ growth stage plants) to support larval growth, although juice was stimulatory in choice tests. The total protein content of whorls in S lines was about 15% higher than in R lines, but the significance of this difference is uncertain, because nutritional tests showed that larval growth increased with total protein only up to 12% protein. Sugars were only slightly stimulatory. Thus, the amino acids along with higher hemicellulose content of R lines, established by us earlier, appear to explain much of the basis of resistance in corn to larval leaf-feeding of the FAW.     

Physiological, Nutritional, and Biochemical Bases of Corn Resistance to Foliage-Feeding Fall Armyworm

Three corn (Zea mays) germplasm lines [i.e., Ab24E (susceptible control), Mp708 (resistant control), and a locally selected partial inbred line FAW7050 (resistant)] were examined for Spodoptera frugiperda (J.E. Smith; Lepidoptera: Noctuidae) resistance. Nutritional [i.e., total protein content, amino acids, glucose, total nonstructural carbohydrates (TNC), protein to TNC (P/C) ratios] and biochemical (i.e., peroxidase and lipoxygenase 3) properties in the seedlings of these corn lines were examined to categorize resistance mechanisms to S. frugiperda. Physiological changes in photosynthetic rates also were examined in an attempt to explain nutritional and biochemical dynamics among corn germplasm lines and between insect-infested and noninfested corn plants within a germplasm line. Results indicated that S. frugiperda larvae survived better and developed faster in susceptible Ab24E than in resistant FAW7050 or Mp708. The three germplasm lines differed in resistance mechanisms to S. frugiperda, and the observed patterns of resistance were probably collective results of the P/C ratio and defensive proteins. That is, the susceptibility of Ab24E to S. frugiperda was due to a high P/C ratio and a low level of induced defensive compounds in response to insect herbivory, while the resistance of FAW7050 resulted from elevated defensive proteins following insect herbivory, low P/C ratio, and elevated defensive proteins in Mp708 contributed to its resistance to S. frugiperda. The elevated protein amounts in resistant Mp708 and FAW7050 following S. frugiperda injury were likely due to greater conversion of photosynthates to defensive proteins following the greater photosynthetic rates in these entries. Greater photosynthetic capacity in Mp708 and FAW7050 also led to higher amino acid and glucose contents in these two lines. Neither amino acid nor lipoxygenase 3 played a critical role in corn resistance to S. frugiperda. However, high inducibility of peroxidase may be an indicator of S. frugiperda susceptibility as observed elsewhere.     

2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one (N-O-Me-DIMBOA), a possible toxic factor in corn to the southwestern corn borer

The southwestern corn borer (SWCB),Diatraea grandiosella Dyar, is a major pest of corn,Zea mays L., in the southern United States. The damage to corn is caused primarily by larval feeding on leaf, ear, and stem tissues. In this study, 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one (N-O-Me-DIMBOA) was identified by MS and NMR as present in corn whorl surface waxes. This compound has evidently not been isolated previously, but its glucoside has been reported in corn, wheat, andCoix lachryma. It is present in the waxes in a higher concentration than DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) and 6-MBOA (6-methoxybenzoxazolinone). It was toxic to the SWCB in a stress diet, but it was less toxic to this insect than 6-MBOA when incorporated in the standard rearing diet. Nevertheless, it may have some role in the resistance of corn to the SWCB because the total surface wax content is higher in resistant lines than in susceptible lines.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Arrestant responses of southwestern corn borer larvae to free amino acids: Structure-activity relationships

The leaf-feeding resistance of corn or maizeZea mays L. to the southwestern corn borer, SWCB,Diatraea grandiosella Dyar has been attributed at least in part to decreased protein, increased crude fiber, and increased hemicellulose in the whorls of resistant genotypes. In this study, individual amino acids and sugars were evaluated as arrestants, with the objective of identifying those that gave weak or negative responses. Several structure-activity relationships were identified. Larvae responded to three-carbonn alkyl alpha amino acids more than to two-, four-, five-, and six-carbon compounds. Amino acids with terminal isopropyl functions gave decreased responses relative to theirn-alkyl counterparts. Dicarboxylic acids and their amides gave the lowest responses of all classes of amino acids. The normally occurring basic amino acids were all good arrestants. The guanido [HN:C(NH₂)NH-] function was somewhat important to an arrestant response, as was the number of methylenes between the alpha and omega amino functions of diaminon-alkyl amino acids. Hydroxy amino acids were generally good arrestants unless the hydroxyl was located on a ring system. The two sugars present in expressed corn whorl juice, glucose and fructose, gave poor responses. However, two other sugars, mannose and arabinose, whose C-2 hydroxyls are conformationally in the axial position, were strongly arrestant. Formulated amino acid mixtures based on their content in whorl juice were as strong arrestants as whorl juice. However, the relative contributions of amino acids and sugars that are weak arrestants to the resistance of corn to SWCB larvae is uncertain because amino acid analyses did not reveal significantly higher contents of these amino acids in the whorl juices of resistant lines.     

Sources of fall armyworm,Spodoptera frugiperda (Lepidoptera: Noctuidae), kairomones eliciting host-finding behavior inCotesia (=Apanteles) marginivenitris (Hymenoptera: Braconidae)

Bioassay responses inCotesia marginiventris (Cresson) females to materials derived from fall armyworm (FAW) larvae,Spodoptera frugiperda (J. E. Smith), were most intense for frass and somewhat less intense for larval and pupal cutical materials, scales, exuviae, silk, and oral secretion, with FAW larval hemolymph eliciting only a slight response. The highest percentage of ovipositor probing was caused by frass (100%) and moth scales (90%). Various types of corn-leaf damage when assayed alone did not produce responses as intense as when assayed in combination with frass, cuticle material, and oral secretion. Parasitoid response was somewhat better to frass derived from FAW larvae feeding on corn and peanut leaves than from larvae feeding on the foliage of soybeans, Bermuda grass, cowpeas, or laboratory diet. Hexane and chloroform were better than methanol and water for extracting active material from FAW frass, and chloroform was the best of these solvents for extracting corn leaves. Serial dilutions of frass extracts resulted in a reduction in parasitoid response.This paper was submitted in partial fulfillment of the requirements for Doctor of Philosophy, Department of Entomology and Nematology, University of Florida, Gainesville.     

Phytotoxin Production and Phytoalexin Elicitation by the Phytopathogenic Fungus Sclerotinia sclerotiorum

The fungus Sclerotinia sclerotiorum (Lib.) de Bary causes rot disease in a vast range of plant families, including Cruciferae (Brassicaceae). We investigated the production of phytotoxins by S. sclerotiorum by using a bioassay-guided isolation, as well as the phytoalexins produced by the resistant wild crucifer Erucastrum gallicum under elicitation by S. sclerotiorum and other agents. We established for the first time that S. sclerotiorum produces a somewhat selective phytotoxin, sclerin, which is phytotoxic to three cruciferous species (Brassica napus, B. juncea, and Sinapis alba) susceptible to Sclerotinia stem rot disease, causing severe necrosis and chlorosis, but not to a resistant species (Erucastrum gallicum). In addition, we have shown that oleic acid, the major fatty acid isolated from sclerotia of S. sclerotiorum is responsible for the toxic activity of extracts of sclerotia to brine shrimp larvae (Artemia salina). Phytoalexin elicitation in leaves of E. gallicum led to the isolation of three known phytoalexins: indole-3-acetonitrile, arvelexin, and 1-methoxyspirobrassinin. Considering that resistance of E. gallicum to S. sclerotiorum is potentially transferable to B. rapa, a susceptible canola species, and that arvelexin, and 1-methoxyspirobrassinin are not produced by B. rapa, these phytoalexins may become useful markers for resistance against S. sclerotiorum.     

Effects of mite resistance mechanism of geraniums on mortality and behavior of foxglove aphid (Acyrthosiphon solani Kaltenbach)

Geraniums (Pelargonium xhortorum Bailey) possess a pest-resistance mechanism, based on glandular trichomes and the exudate they produce, that has been shown to be effective against the two-spotted spider mite (Tetranychus urticae Koch). Using an intact plant bioassay, the effectiveness of the resistance mechanism was determined for another potential pest, the foxglove aphid (Acyrthosiphon solani Kaltenbach). Comparisons were made between plant lines previously analyzed for their degree of resistance to mites, as well as their glandular trichome density and trichome exudate production. Over 100 aphid adults were bioassayed on each of the five plant lines used in the experiment. In addition to adult aphid survival, the production and survival of nymphs was determined in this bioassay. The results indicate that plant lines that are resistant to the two-spotted spider mite are also resistant to the foxglove aphid, while lines susceptible to mites are susceptible to the aphids. To evaluate the physical impediment features of the trichome exudate, the behavior of foxglove aphid nymphs was compared on two geranium lines, one a resistant line with high trichome densities and large quantities of exudate and the second a susceptible line with few trichomes and reduced exudate. A third leaf surface type was produced by washing the exudate from resistant leaves using a mildly basic buffer solution prior to the bioassay. Aphid behavior was divided into five categories: feeding or probing, resting, wandering, struggling, and immobilized. On both susceptible leaves and resistant leaves from which the exudate had been removed by washing, the aphids settled quickly and were observed with inserted stylets during most of the observation intervals. In contrast, aphids on the unwashed resistant leaf surfaces often became ensnared in the sticky trichome exudate and had difficulty in settling to probe the leaf. Physical entrapment by glandular trichome exudate appears to be an important aspect of aphid resistance in geraniums.     

Detoxification of cereal plant allelochemicals by aphids: Activity and molecular weights of glutathioneS-transferase in three species of cereal aphids

The activity and molecular weights of glutathioneS-transferase were studied in three species of cereal aphid:Metopolophium dirhodum, Sitobion avenae, andRhopalosiphum padi. The highest level of glutathioneS-transferase activity was recorded in extracts fromM. dirhodum and the lowest fromS. avenae, and extracts of larvae were more active than those from adults. The activity of this enzyme was higher in extracts ofS. avenae andR. padi previously fed on a moderately resistant wheat variety than on a susceptible variety. Gel filtration followed by SDS-PAGE revealed three protein bands in the active fractions. The first had a molecular weight of 28,500 and the second of 27,500 and were present in all three species of aphid. The third protein differed in the three species, having a molecular weight of 26,000 inS. avenae, 25,500 inM. dirhodum, and 24,000 inR. padi.     

Development of a bioassay to test phloem sap samples from lettuce for resistance toNasonovia ribisnigri (homoptera,aphididae)

TheNr-gene-based resistance of lettuce to the aphidNasonovia ribisnigri (Mosley) has previously been shown to be located in the phloem. Since chemical analyses of the phloem sap had shown no differences between resistant and susceptible lines, a bioassay was developed in order to test samples from resistant and susceptible plants on aphid feeding. For this, whole-plant extracts, honeydew, and EDTA-collected phloem extracts were obtained, and a sensitive bioassay was developed using EDTA samples. The EDTA was removed, and samples were added to a simple sucrose solution or to a complex artificial diet and presented in a choice situation comparing extracts from resistant and susceptible plants. EDTA-collected phloem sap samples from susceptible plants were preferred to those from resistant plants. The resistance is probably based on a feeding deterrent activity of the phloem sap in the resistant plant.     

Behavioral and biological responses ofCotesia marginiventris to kairomones of the fall armyworm,Spodoptera frugiperda

Potential kairomone sources of the fall armyworm (FAW),Spodoptera frugiperda (J.E. Smith), were bioassayed with females ofCotesia marginiventris (Cresson) in Petri dishes (10 cm diam). MatedC. marginiventris females, ranging in age from 1 to 3 days exhibited the most intense bioassay responses to potential sources of kairomone. Contacting a FAW-damaged corn leaf modified the pattern of movement inC. marginiventris from random to one exhibiting a significant increase in klinokinesis. No significant differences were present in kairomone responses of nonconditioned and conditioned parasitoids and parasitoid response to kairomones did not change throughout the photophase (0800–1800 hr). Removal of one, both, or the first eight antennal segments reduced or eliminated the response of the parasitoid to kairomones. Female parasitoids did not exhibit a preference for corn leaves damaged by a particular fall armyworm instar and parasitization rates were highest in larvae 48 hr old.Submitted in partial fulfillment of the requirements for Doctor of Philosophy, Department of Entomology and Nematology, University of Florida, Gainesville.     

Response ofDiabrotica virgifera virgifera,D. v. Zeae,andD. porracea to stereoisomers of 8-methyl-2-decyl propanoate

The four stereoisomers of 8-methyl-2-decyl propanoate were tested in the United States and Mexico for attractiveness toDiabrotica virgifera virgifera LeConte, the western corn rootworm,D. v. zeae Krysan and Smith, the Mexican corn rootworm, andD. porracea Harold. Males ofD. v. virgifera andD. v. zeae responded strongly to the (2R,8R)-isomer and secondarily to (2S,8R), whileD. ponacea responded exclusively to the (2S,8R)-isomer. The (2S,8S)- and (2R,8S)-isomers were inactive in all tests. Synergism or inhibition was not detected when various mixtures of the isomers were tested withD. v. virgifera. These phenomena were not tested withD. v. zeae andD. ponacea.Coleoptera: Chrysomelidae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Nitrogen requirements of corn (Zea mays L.) as affected by monocropping and intercropping with Alfalfa (Medicago sativa)

Intercropping perennials with corn has the potential to improve utilization of the growing season over monocropping corn in regions where a substantial portion of the growing season is too cool for corn growth. The biomass potential and fertilizer N requirements of monocropped corn (Zea mays) grown using conventional tillage were compared with those of corn intercropped with alfalfa (Medicago sativa) in 1987 and 1988. The intercropped alfalfa was harvested once prior to planting the corn each spring. Rotation effects on and N fertilizer requirements for monocropped corn following these treatments and also following monocropped alfalfa, were evaluated in 1989 and 1990. During the two years of intercropping for which data is presented, the critical intercropped corn biomass (13.05 Mg ha^–1) estimated using a quadratic-plus plateau model, was close to the monocropped corn biomass (13.01 Mg ha^–1), but an estimated 83 kg ha^–1 more N was required for intercropped corn to reach the critical biomass. Total biomass (intercropped corn and alfalfa) was 25% greater than that of the monocropped corn, and the total N uptake was 55% greater than that by monocropped corn over the two- year period. After rotation to monocropped corn using conventional tillage in 1989, corn biomass averaged over N rates following intercropping or monocropped corn was lower (P=0.01) than following monocropped alfalfa. Critical corn biomass estimated was highest following alfalfa and lowest following monocropped corn, and more N fertilizer was required to attain the critical biomass under continuous monocropped corn in 1989. Corn yields and N uptake values in 1990 were not significantly different among the cropping systems. The N fertilizer replacement values due to intercropping decreased from above 90 kg N ha^–1 in the first year of rotation to less than 40 kg N ha^–1 in the second year of rotation. Considering the higher potential for total biomass production and rotation benefit, intercropping is a viable alternative to conventional corn monoculture for forage production.     

Inhibition ofCampoletis sonorensis parasitism ofHeliothis zea and of parasitoid development by 2-tridecanone-mediated insect resistance of wild tomato

Field populations ofHeliothis spp. were sampled for levels of naturally occurring larval parasitism on six tomato lines varying in levels of 2-tridecanone-mediated resistance toManduca sexta (L.) andLeptinotarsa decemlineata (Say). Second and third instars were parasitized byCampoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) andCotesia (=Apantales)marginiventris (Cresson) (Hymenoptera: Braconidae) in 1984 through 1986 and byMicropletis croceipes (Cresson) (Hymenoptera: Braconidae) in 1986. Differences in parasitism by individual and multiple species among host plants were not demonstrated. However, levels of parasitism were low and variable among replicates. Total larval parasitism averaged across all plant lines was less than 6% in 1984 and 1986 and approximately 11% in 1985. In laboratory cage studies,C. sonorensis parasitized fewerH. zea larvae on tomato foliage with high levels of 2-tridecanone than on foliage with low levels. RearingH. zea on diet containing 2-tridecanone and 2-undecanone did not alter incidence of parasitism byC, sonorensis; nor did rearing parasitizedH. zea larvae on chemically treated host diets precondition the parasitoid to higher or lower mortality when transferred to foliage as a substrate for cocoon spinning, regardless of the foliage genotype. However, parasitoid survival during cocoon spinning on foliage varied significantly among plant lines in a manner corresponding to the level of 2-tridecanone-mediated resistance of the foliage. Parasitoid mortality was greatest on highly resistant foliage and lowest on susceptible foliage.     

Sex pheromone of fall armyworm

Two components of the fall armyworm,Spodoptera frugiperda (J.E. Smith), sex pheromone, (Z)-9-dodecen-1-ol acetate (DDA) and (Z)-9-tetradecen-1-ol (TDA), were tested alone and in combination to determine their effects on male sexual response and inhibition of mating in the laboratory. The threshold response for FAW males was lower for TDA than for DDA, and males responded to TDA over a wider range of dosages. Although TDA is not attractive to FAW males in the field, this compound was highly effective in reducing mating under laboratory conditions.cooperating with the Insect Attractants, Behavior, and Basic Biology Research Laboratory, Gainesville, Florida 32604.     

Effects of cotton plant allelochemicals and nutrients on behavior and development of tobacco budworm

Female moths of the tobacco budworm,Heliothis virescens (F.), oviposit in the terminals of the cotton plant,Gossypium hirsutum (L.). The hatched larvae migrate to the terminal area and then to small squares (buds), on which they feed, finally burrowing into the anthers where they grow and develop. They attempt to avoid gossypol glands as they feed. Chemically related evidence explains, in part, these observations. The calyx crown of resistant lines (which is avoided) is high in the terpenoid aldehydes (TAs) including gossypol. HPLC data showed that the gossypol content of both susceptible and resistant glanded lines is equal, while the hemigossypolone and heliocides H₁ and H₂ are greatly increased in resistant lines and presumably are more closely associated with resistance. Analysis for total amino acids in cotton square tissues showed that there was a gradation from the calyx and calyx crown, which were lowest, to the anthers, the site of final insect development, which were highest. Synthetic diets mimicking amino acid distribution in anthers were found to be successful for larval growth and development.     

Toxicity of allelochemicals from wild insect-resistant tomatoLycopersicon hirsutum f.glabratum toCampoletis sonorensis,a parasitoid ofHeliothis zea

Greenhouse-grown plants of five tomato lines varying in their level of 2-tridecanone-mediated resistance toManduca sexta (L.) andLeptinotarsa decemlineata (Say) were found to adversely affect larvae ofCampoletis sonorensis (Cameron), a larval endoparasitoid ofHeliothis zea (Boddie), in a manner directly related to their level of resistance. The parasitoid larvae, which emerge as fifth instars from their host and construct a cocoon on the foliage of their hosts' host plant, suffered extensive mortality during cocoon spinning on highly resistant foliage. Mortality was greatest (82%) on the highly resistant plants ofLycopersicon hirsutum f.glabratum (accession PI 134417) and an F₁ backcross [(L. esculentum × PI 134417) × PI 134417] selection. Mortality was intermediate (40 and 28%, respectively) on backcross selections with moderate and low levels of resistance and least (8%) on susceptibleL. esculentum. Removal of the glandular trichomes, which contain 2-tridecanone in their tips, from the foliage eliminated differences in parasitoid mortality among plant lines.Bioassays of 2-tridecanone indicated that it is acutely toxic to fifth instarC. sonorensis larvae at the quantities associated with highly resistant foliage and produces symptoms identical to those observed on resistant foliage. 2-Undecanone, a second methyl ketone present in the glandular trichomes of resistant foliage, was also toxic toC. sonorensis larvae, but significantly less so than 2-tridecanone. The results support the hypothesis that 2-tridecanone is responsible for the observed mortality ofC. sonorensis larvae during cocoon construction on resistant foliage.     

How contact foraging experiences affect preferences for host-related odors in the larval parasitoidCotesia marginiventris (Cresson) (Hymenoptera: Braconidae)

Responses of individual females of the parasitoidCotesia marginiventris to the odors of four different complexes of host larvae feeding on leaves were observed in a four-arm olfactometer. The plant-host complexes were composed of fall armyworm (FAW) larvae or cabbage looper (CL) larvae feeding on either corn or cotton seedlings. Prior to testing, each female was given a brief foraging experience on a plant-host complex and was then exposed to the odors of the same complex in the olfactometer. The experienced females responded to familiar odors in a dose-related manner, and these responses were virtually identical to all four complexes. Preferences for the odors of one of two plant-host complexes were tested in dual choice situations. Generally, FAW odors were preferred over CL odors and corn odors over cotton odors. A short foraging experience significantly affected the females' odor preferences in favor of the odors released by the experienced complex. Additional experiments revealed that neither longer bouts of experience nor bouts that included ovipositions resulted in a stronger change in preference. Experience affected preference in combinations where only the host species was varied as well as in combinations where only the plant species was varied. The results, therefore, strongly indicate that both the plants and the hosts somehow are involved in the production and/or release of the semiochemicals that attractC. marginiventris.Mention of a proprietary product does not constitute an endorsement or the recommendation for its use by the USDA.     

ACQUIRED AND R-GENE-MEDIATED RESISTANCE AGAINST THE POTATO APHID IN TOMATO

We examined the effects of three forms of host plant resistance in tomato, Lycopersicon esculentum, on the potato aphid, Macrosiphum euphorbiae. Mi-1.2, a resistance gene (R-gene) in tomato that deters aphid feeding, reduced the population growth of both potato aphid isolates tested, although it appeared to have a greater impact on isolate WU11 than on isolate WU12. The results suggest that there may be quantitative differences in virulence between these two aphid isolates. We also examined two distinct forms of acquired resistance in tomato, jasmonic acid (JA)-dependent and salicylic acid (SA)-dependent induced defenses. Exogenous foliar application of JA triggered expression of a JA-inducible proteinase inhibitor in tomato cultivars with and without Mi-1.2, although the effects of treatment on aphid performance differed between these cultivars. JA-treatment reduced aphid population growth on a susceptible tomato cultivar that lacks Mi-1.2, but did not significantly enhance or inhibit aphid control on a near-isogenic resistant tomato cultivar that carries this gene. Foliar application of an SA analog, benzothiadiazole (BTH), was used to induce SA-dependent defenses. BTH treatment reduced the population growth of both aphid isolates on a susceptible tomato cultivar, and also enhanced aphid control on a resistant cultivar. The results indicate that both SA- and JA-dependent acquired resistance in tomato have a direct negative effect on a phloem-feeding insect. Furthermore, this study demonstrates that acquired resistance and R-gene-mediated resistance can interact for enhanced suppression of insect herbivores.     

Possible roles of cotton bud sugars and terpenoids in oviposition by the boll weevil

Several cottonGossypium spp. race stocks have been identified that possess resistance to the boll weevilAnthonomus grandis Boh. because oviposition is decreased. In this work, a number of known cotton constituents that influence stimulation of feeding and attractancy for this insect were found to have little or no influence on oviposition. These include gossypol, -bis-abolol, caryophyllene, some fatty acids and their methyl esters, some wax esters, flavonoids, condensed tannins, and chrysanthemin. Analysis of cotton bud surfaces showed that the content of volatile terpenoids was generally higher in resistant lines, but bioassays did not show decreased oviposition in the presence of the terpenoids. The sugars (glucose, fructose, and sucrose) found in anthers, uniformly stimulated oviposition in the bioassay, and their content was higher in susceptible lines. These results suggest that a major basis of resistance to boll weevils as related to oviposition may be the decreased content of sugars in resistant lines. The analysis of free sugars in the anthers, and perhaps also the analysis of bud surface terpenoids, may provide a basis for selection or genetic production of cotton lines resistant to the boll weevil.     

Volatile compounds from crabapple (Malus spp.) cultivars differing in susceptibility to the Japanese beetle (Popillia japonica Newman)

The volatile compounds emitted by leaves of four crabapple cultivars susceptible to damage by Japanese beetles and four relatively resistant cultivars were examined. Twelve compounds, mostly terpene hydrocarbons, were identified from intact leaves. The terpenes (E)--ocimene, caryophylene, germacrene D and (E,E)--farnesene occurred in significantly higher levels in susceptible cultivars, whereas resistant cultivars produced greater amounts of (E)-4,8-dimethyl 1,3,7-nonatriene and linalool. The relative attractiveness of the cultivars as determined in a pitfall bioassay, however, was not related to their susceptibility to the Japanese beetle as previously determined by defoliation sustained in the field. The attractiveness of individual cultivars was found to be positiviely correlated with linalool as a percent of the total volatile blend emitted by leaves. This study and previous work suggest that variation in susceptibility of crabapple cultivars to defoliation by Japanese beetles is not due to the attractiveness of the individual cultivars but rather to nonvolatile components of susceptibility and/or resistance. A scenario for host location by the Japanese beetle is presented.