Tryptamine-induced resistance in tryptophan decarboxylase transgenic poplar and tobacco plants against their specific herbivores

The presence of amines and their derivatives in plant tissues is known to influence insect feeding and reproduction. The enzyme tryptophan decarboxylase (TDC) catalyzes the decarboxylation of tryptophan to tryptamine, which is both a bioactive amine and a precursor of other indole derivatives. Transgenic poplar and tobacco plants ectopically expressing TDC1 accumulated elevated levels of tryptamine without affecting plant growth and development. This accumulation was consistently associated with adverse effects on feeding behavior and physiology of Malacosoma disstria Hub. (forest tent caterpillar, FTC) and Manduca sexta L. (tobacco hornworm, THW). Behavior studies with FTC and THW larvae showed that acceptability of the leaf tissue to larvae was inversely related to foliar tryptamine levels. Physiological studies with FTC and THW larvae showed that consumption of leaf tissue from the transgenic lines is deleterious to larvae growth, apparently due to a postingestive mechanism. Thus, ectopic expression of TDC1 can allow sufficient tryptamine to accumulate in poplar and tobacco leaf tissue to suppress significantly the growth of insect pests that normally feed on these plants.     

Effects of elevated CO<Subscript>2</Subscript> on foliar quality and herbivore damage in a scrub oak ecosystem

Atmospheric CO₂ concentrations have increased exponentially over the last century and continuing increases are expected to have significant effects on ecosystems. We investigated the interactions among atmospheric CO₂, foliar quality, and herbivory within a scrub oak community at the Kennedy Space Center, Florida. Sixteen plots of open-top chambers were followed; eight of which were exposed to ambient levels of CO₂ (350 ppm), and eight of which were exposed to elevated levels of CO₂ (700 ppm). We focused on three oak species, Quercus geminata, Quercus myrtifolia, Quercus chapmanii, and one nitrogen fixing legume, Galactia elliottii. There were declines in overall nitrogen and increases in C:N ratios under elevated CO₂. Total carbon, phenolics (condensed tannins, hydrolyzable tannins, total phenolics) and fiber (cellulose, hemicellulose, lignin) did not change under elevated CO₂ across plant species. Plant species differed in their relative foliar chemistries over time, however, the only consistent differences were higher nitrogen concentrations and lower C:N ratios in the nitrogen fixer when compared to the oak species. Under elevated CO₂, damage by herbivores decreased for four of the six insect groups investigated. The overall declines in both foliar quality and herbivory under elevated CO₂ treatments suggest that damage to plants may decline as atmospheric CO₂ levels continue to rise.     

Differential activity and degradation of plant volatile elicitors in regurgitant of tobacco hornworm (Manduca sexta) larvae

Plants respond to insect herbivory by emitting volatile compounds that attract natural enemies of the herbivores. Biosynthesis of many of these volatiles in plants is induced by herbivore-produced compounds. Components of tobacco hornworm (THW) regurgitant were investigated for their efficacy as elicitors of corn seedling volatiles. Two components that elicited the strongest release of volatiles were isolated and identified as N-linolenoyl-L-glutamine (18:3-GLN) and N-linolenoyl-L-glutamic acid (18:3-GLU). The approximately 10 times more active 18:3-GLN, which also is found in the regurgitant of several other Lepidopteran larvae, was rapidly degraded when THW regurgitant was left at room temperature, while 18:3-GLU degraded at a much slower rate. Different dietary sources of THW and tobacco bud worm larvae, including both host and nonhost plants, did not affect the amino acid composition of the fatty acid–amino acid conjugates in the regurgitant.     

Effects of Elevated Carbon Dioxide and Ozone on Foliar Proanthocyanidins in Betula platyphylla, Betula ermanii, and Fagus crenata Seedlings

Proanthocyanidins (PAs) or condensed tannins are a major group of phenolic compounds in the leaves of birch trees and many other woody and herbaceous plants. These compounds constitute a significant allocation of carbon in leaves and are involved in plant responses to environmental stress factors, such as pathogens or herbivores. In some plants, PA concentrations are affected by atmospheric carbon dioxide (CO₂) and ozone (O₃) levels that may influence, for example, species fitness, community structure, or ecosystem nutrient cycling. Therefore, a study on the quantitative response of PAs to elevated concentrations of carbon dioxide (CO₂) and ozone (O₃) was undertaken in seedlings of Betula platyphylla, Betula ermanii, and Fagus crenata. Seedlings were exposed to ambient or elevated O₃ and CO₂ levels during two growing seasons in the Kanto district in Japan. Ten open-top chambers were used for five different treatments with two replicates: filtered air (FA), ambient air (ambient O₃, 43 ppb; ambient CO₂, 377 ppm), elevated O₃ (1.5 × ambient O₃, 66 ppb), elevated CO₂ (1.5 × ambient CO₂, 544 ppm), and elevated O₃ and CO₂ combined. In addition, seedlings growing in natural conditions outside of chambers were studied. Leaf samples were analyzed for total PA concentrations by butanol–HCl assay and for polymeric PA concentrations by normal-phase high-performance liquid chromatography. Total PA concentrations in leaves of all species were similarly affected by different treatments. They were significantly higher in seedlings treated with elevated CO₂ and O₃ combined, and in seedlings growing outside chambers compared with the FA controls. F. crenata contained only traces of polymeric PAs, but significant species × treatment interaction was observed in the polymeric PA concentrations in B. ermanii and B. platyphylla. In B. platyphylla, leaves treated with elevated CO₂ + O₃ differed significantly from all other treatments. It was suggested that the strongest effect of elevated CO₂ and O₃ combined on leaf PA contents resulted from the additive effect of these environmental factors on phenolic biosynthesis.     

Systemic induction of feeding deterrents in cotton plants by feeding ofSpodoptera SPP. Larvae

Cotton,Gossypium hirsutum L., has been shown to exhibit systemic induced resistance to arthropods under certain conditions. We conducted experiments to determine the effects of previous feeding ofSpodoptera exigua Hübner andSpodoptera littoralis (Boisd.) larvae on feeding behavior, growth, and survival of larvae subsequently feeding on cotton. In one feeding choice test,S. exigua larvae preferred young leaves from undamaged control plants to undamaged young leaves from a previously damaged plant. Feeding deterrence was noticeable after only 6 hr of initial feeding damage by larvae, and there was almost complete deterrence after 30 and 54 hr of continuous feeding. In a second feeding choice test,S. littoralis larvae fed more on mature leaves from undamaged control plants than on undamaged mature leaves from previously damaged plants. In no-choice tests, third instars ofS. littoralis fed undamaged young leaves from damaged plants did not gain weight and died by the seventh day, whereas larvae fed young leaves from undamaged control plants gained weight and pupated within 11 days. Sixth instars ofS. littoralis fed either old damaged leaves, old undamaged leaves, or young undamaged leaves all from previously damaged plants gained weight slowly and took more than 12 days to pupate, whereas larvae fed young leaves from undamaged plants gained weight rapidly and pupated within five days of the beginning of the experiment.     

Effects of Elevated CO<Subscript>2</Subscript> and Herbivore Damage on Litter Quality in a Scrub Oak Ecosystem

Atmospheric CO₂ concentrations have increased dramatically over the last century and continuing increases are expected to have significant, though currently unpredictable, effects on ecosystems. One important process that may be affected by elevated CO₂ is leaf litter decomposition. We investigated the interactions among atmospheric CO₂, herbivory, and litter quality within a scrub oak community at the Kennedy Space Center, Florida. Leaf litter chemistry in 16 plots of open-top chambers was followed for 3 years; eight were exposed to ambient levels of CO₂, and eight were exposed to elevated levels of CO₂ (ambient + 350 ppmV). We focused on three dominant oak species, Quercus geminata, Quercus myrtifolia, and Quercus chapmanii. Condensed tannin concentrations in oak leaf litter were higher under elevated CO₂. Litter chemistry differed among all plant species except for condensed tannins. Phenolic concentrations were lower, whereas lignin concentrations and lignin/nitrogen ratios were higher in herbivore-damaged litter independent of CO₂ concentration. However, changes in litter chemistry from year to year were far larger than effects of CO₂ or insect damage, suggesting that these may have only minor effects on litter decomposition.     

Effects of comsumption of high and low nicotine tobacco byManduca sexta (Lepidoptera: Sphingidae) on survival of gregarious endoparasitoidCotesia congregata (Hymenoptera: Braconidae)

The significance of nicotine in the three trophic level interaction involving tobacco (Nicotiana tabacum), the tobacco hornworm (Manduca sexta), and the parasitoidCotesia congregata was investigated in field plots of two varieties of tobacco which had about a 10-fold difference in their nicotine content. WhileM. sexta mortality, rates of parasitism byC. congregata, and the total number ofC. congregata larvae produced per host were similar on each of the two varieties, the number of parasitoids reaching adult-hood on the low nicotine treatment was nearly twice that on the high nicotine treatment. This difference was due to the significantly greater proportion of parasitoid larvae which failed to emerge from the host or that died prior to pupation after emerging from hosts which fed on the high nicotine variety. A greater proportion of larvae from hosts which fed on the low nicotine tobacco died as pupae. No treatment differences occurred for either sex of the parasitoid in individual dry weight, longevity, or pupal development time, except that female pupal duration was prolonged in the high nicotine treatment. These results support the suggestion that plant allelochemicals, which may function to provide plant resistance against pest herbivores, can be detrimental to natural enemies of the pest.Scientific article No. A4148 of the Maryland Agricultural Experiment Station, Department of Entomology. Research supported by NSF grant BSR-84-00614.     

Ovipositional response of tobacco budworm moths (Lepidoptera: Noctuidae) to cuticular labdanes and sucrose esters from the green leaves ofNicotiana glutinosa L. (Solanaceae)

Field plots of three accessions ofNicotiana glutinosa L. (Nicotiana species accessions 24, 24A, and 24B) at Oxford, North Carolina and Tifton, Georgia were heavily damaged by natural populations of tobacco budworms,Heliothis virescens (F.), during 1985–1989. Experiments in outdoor screen cages demonstrated that all accessions ofN. glutinosa were as prone to oviposition byH. virescens moths as was NC 2326, a commercial cultivar of flue-cured tobacco,N. tabacum L. However, in greenhouse experiments, tobacco budworm larvae did not survive or grow as well when placed on plants ofN. glutinosa as they did when placed on plants of NC 2326. Four labdane diterpenes (manool, 2-hydroxymanool, a mixture of sclareols, and labda-13-ene-8,15-diol [labdenediol]) and two sucrose ester fractions (2,3,4-tri-O-acyl-3-O-acetyl-sucrose [G-SE-I] and 2,3,4,-tri-O-acyl-sucrose [G-SE-II]) were isolated from green leaves of the three accessions ofN. glutinosa. These components were bioassayed for their effects on the ovipositional behavior of tobacco budworm moths using small screen cages in a greenhouse at Oxford, North Carolina. Labdenediol, manool, and both sucrose ester fractions stimulated tobacco budworm moths to oviposit on a tobacco budworm-resistant Tobacco Introduction, TI 1112 (PI 124166), when these materials were sprayed onto a leaf.This article reports the results of research only. Mention of a proprietary product does not constitute endorsement or recommendation for its use by USDA, ARS, or by the North Carolina Agricultural Research Service.     

Plant Phenolics as Dietary Antioxidants for Herbivorous Insects: A Test with Genetically Modified Tobacco

High foliar phenolics are generally assumed to increase resistance to insect herbivores, but recent studies show that tobacco lines modified to over– and underexpress phenolics do not exhibit higher constitutive resistance to caterpillars. This is contrary to the expectation that ingestion of tobacco phenolics, particularly chlorogenic acid, should cause oxidative stress in herbivores. We investigated free radical production and antioxidant capacity of fresh crushed leaves of tobacco lines exhibiting over a sixfold difference in chlorogenic acid content to test whether high phenolic concentrations are associated with increased production of reactive oxygen species (ROS). The effects of in planta phenolic levels on feeding behavior, growth, biochemical markers of oxidative stress, and the antioxidant capacity of midgut fluid and hemolymph were assessed in tobacco budworm, Heliothis virescens. The experiments showed that high phenolic foliage was more prooxidant than low phenolic foliage, but the net balance in crushed tissue was antioxidant in comparison to buffer and the commercial antioxidant standard, Trolox. In H. virescens, the antioxidant capacity of midgut fluid was also powerful, and caterpillars fed high phenolic foliage did not exhibit the expected markers of oxidative stress in midgut tissues (altered ascorbate ratios, disulfides, or total hydroperoxides). Instead, hemolymph of larvae fed high phenolic foliage exhibited improved total Trolox equivalent antioxidant capacity (TEAC). These results suggest that the elevated foliar phenolics in some plants may have beneficial antioxidant properties for herbivorous insects, much as dietary phenolics do in mammals.     

Spectrum of Cyanide Toxicity and Allocation in <Emphasis Type="Italic">Heliconius erato</Emphasis> and <Emphasis Type="Italic">Passiflora</Emphasis> Host Plants

The larvae of three races of Heliconius erato were fed various species of Passiflora containing varying levels of cyanoglucosides. The mortality rate of larvae and pupae rose when larvae were fed species of Passiflora capable of releasing larger quantities of cyanide. When larvae were fed species of Passiflora with these properties, the resulting adult butterflies also released higher levels of cyanide. This may serve as a defense mechanism. The compounds responsible for the release of cyanide were not evenly distributed throughout the adult butterfly’s body. The thorax contained the highest concentration of cyanogenic substances, followed by the head, wings, and abdomen. The younger tissues of Passiflora plants had higher levels of cyanide-releasing compounds than stems and mature leaves. Cyanogenic glycoside distribution within the plants is consistent with optimal allocation theory. The levels of cyanide-releasing substances in plants varied depending on the season.     

Impact of Elevated Levels of Atmospheric CO<Subscript>2</Subscript> and Herbivory on Flavonoids of Soybean (<Emphasis Type="Italic">Glycine max</Emphasis> Linnaeus)

Atmospheric levels of carbon dioxide (CO₂) have been increasing steadily over the last century. Plants grown under elevated CO₂ conditions experience physiological changes, particularly in phytochemical content, that can influence their suitability as food for insects. Flavonoids are important plant defense compounds and antioxidants that can have a large effect on leaf palatability and herbivore longevity. In this study, flavonoid content was examined in foliage of soybean (Glycine max Linnaeus) grown under ambient and elevated levels of CO₂ and subjected to damage by herbivores in three feeding guilds: leaf skeletonizer (Popillia japonica Newman), leaf chewer (Vanessa cardui Linnaeus), and phloem feeder (Aphis glycines Matsumura). Flavonoid content also was examined in foliage of soybean grown under ambient and elevated levels of O₃ and subjected to damage by the leaf skeletonizer P. japonica. The presence of the isoflavones genistein and daidzein and the flavonols quercetin and kaempferol was confirmed in all plants examined, as were their glycosides. All compounds significantly increased in concentration as the growing season progressed. Concentrations of quercetin glycosides were higher in plants grown under elevated levels of CO₂. The majority of compounds in foliage were induced in response to leaf skeletonization damage but remained unchanged in response to non-skeletonizing feeding or phloem-feeding. Most compounds increased in concentration in plants grown under elevated levels of O₃. Insects feeding on G. max foliage growing under elevated levels of CO₂ may derive additional antioxidant benefits from their host plants as a consequence of the change in ratios of flavonoid classes. This nutritional benefit could lead to increased herbivore longevity and increased damage to soybean (and perhaps other crop plants) in the future.     

Biochemical insight into insecticidal properties ofl-Canavanine,a higher plant protective allelochemical

l-Canavanine manifests potent insecticidal properties in a canavanine-sensitive insect such as the tobacco hornworm,Manduca sexta (L.) (Sphingidae). Investigations of the biochemical basis for the antimetabolic properties of this arginine analog reveal that it is activated and aminoacylated by arginyl tRNA synthetase and incorporated into the nascent polypeptide chain. This creates structurally aberrant, canavanine-containing proteins that can possess altered physicochemical properties. Evidence is presented in studies with the tobacco hornworm; the canavanine-adapted bruchid beetle,Caryedes brasiliensis (Bruchidae) and the weevil,Sternechus tuberculatus (Curculionidae); as well as the canavanine-resistant larvae ofHeliothis virescens [Noctuidae] to support the contention that formation of aberrant, canavanyl proteins produce deleterious biological effects and is a significant basis for canavanine's antimetabolic properties.     

Detoxication activity in the gypsy moth: Effects of host CO2 and NO 3 − availability

We investigated the effects of host species and resource (carbon dioxide, nitrate) availability on activity of detoxication enzymes in the gypsy moth,Lymantria dispar. Larvae were fed foliage from quaking aspen or sugar maple grown under ambient or elevated atmospheric CO₂, with low or high soil NO ₃ ^– availability. Enzyme solutions were prepared from larval midguts and assayed for activity of cytochrome P-450 monooxygenase, esterase, glutathione transferase, and carbonyl reductase enzymes. Activity of each enzyme system was influenced by larval host species, CO₂ or NO ₃ ^– availability, or an interaction of factors. Activity of all but glutathione transferases was highest in larvae reared on aspen. Elevated atmospheric CO₂ promoted all but transferase activity in larvae reared on aspen, but had little if any impact on enzyme activities of larvae reared on maple. High NO ₃ ^– availability enhanced activity of most enzyme systems in gypsy moths fed high CO₂ foliage, but the effect was less consistent for insects fed ambient CO₂ foliage. This research shows that gypsy moths respond biochemically not only to interspecific differences in host chemistry, but also to resource-mediated, intraspecific changes in host chemistry. Such responses are likely to be important for the dynamics of plantinsect interactions as they occur now and as they will be altered by global atmospheric changes in the future.     

Allelochemics produced by the hydrophyteMyriophyllum spicatum affecting mosquitoes and midges

An extract of the hydrophyteMyriophyllum spicatum L. was found to be toxic to first- and fourth-instar larvae of the mosquitoes,Culex quinquefasciatus Say,Culex tarsalis Coquillett,Culiseta incidens (Thomson),Aedes aegypti L., and chironomid midges in the laboratory. When first-stage larvae were exposed to the extract, the lowest concentration (6.4 mg extract/100 ml H₂O) produced 86,60, and 48% mortality inC. incidens, C. quinquefasciatus, andA. aegypti, respectively. Higher concentrations caused 100% mortality in both first and fourth instars (63.75 mg/100 ml H₂O or more). In general, the biocidal activity of the extract was found to be similar when first- and fourth-stage larvae were exposed. Some mortality in the successive pupal and adult stages was observed when fourth-stage larvae were exposed to the extract, but mortality occurred only in the various larval instars when first instars were exposed. Among the chironomids,Tanytarsus spp. was more tolerant to the extract thanChironomus spp. In addition to the biocidal activity against immature mosquitoes, the extract was found to show a unique activity acting as an attractant to both sexes of adultC. quinquefasciatus andA. aegypti. The response elicited inA. aegypti appeared to be somewhat higher than that inC. quinquefasciatus. In general, the percentage of males responding to water treated with the extract was higher than that of the females. The extract at higher concentrations seemed to show some repellency at the outset to both species, but induced positive responses later on.     

Effect of nitrogen and water treatment on leaf chemistry in horsenettle (Solanum carolinense), and relationship to herbivory by flea beetles (Epitrix spp.) and tobacco hornworm (Manduca sexta)

We studied the interaction between plants (horsenettle; Solanum carolinense) and herbivorous insects (flea beetles; Epitrix spp., and tobacco hornworm; Manduca sexta) by focusing on three questions: (1) Does variation in nitrogen availability affect leaf chemistry as predicted by the carbon-nutrient balance (CNB) hypothesis? (2) Does variation in plant treatment and leaf chemistry affect insect feeding? (3) Is there an interaction between the insect herbivores that is mediated by variation in leaf chemistry? For three successive years (1998-2001), we grew a set of clones of 10 maternal plants under two nitrogen treatments and two water treatments. For each plant in the summer of 2000, we assayed herbivory by hornworms in both indoor (detached leaf) and outdoor (attached leaf) assays, as well as ambient flea beetle damage. Estimates of leaf material consumed were made via analysis of digitized leaf images. We also assayed leaves for total protein, phenolic, and glycoalkaloid content, and for trypsin inhibitor, polyphenol oxidase, and peroxidase activity. Despite strong effects of nitrogen treatment on growth and reproduction, only total protein responded as predicted by CNB. Leaf phenolic levels were increased by nitrogen treatment, polyphenol oxidase activity was decreased, and other leaf parameters were unaffected. Neither hornworm nor flea beetle herbivory could be related to plant treatment or genotype or to variation in any of the six leaf chemical parameters. A negative relationship between flea beetle and hornworm herbivory was found, but was not apparently mediated by any of the measured leaf chemicals. Because leaf resistance was maintained in low nitrogen plants at the apparent expense of growth and reproduction, our results support the concept of a fitness cost of defense, as predicted by the optimal defense hypothesis.     

Impact of polyphenols on growth of the aquatic herbivore Acentria ephemerella

Larvae of Acentria ephemerella live fully submerged, feeding on submersed aquatic angiosperms such as pondweeds (Potamogeton spp.) and Myriophyllum spicatum. Only the latter contains high concentrations of hydrolyzable tannins known to interfere with the growth of insect herbivores. We tested whether larvae grow faster on Potamogeton perfoliatus or M. spicatum and whether this is due to polyphenols in their food source. Larvae originating from the same egg clutch grew faster and larger on P. perfoliatus than on M. spicatum. The same growth response was observed with larvae that spent winter diapause on either P. perfoliatus or M. spicatum. These larvae were fed either with their host plant or the other macrophyte. No prior feeding effect was found, but growth of larvae reared on M. spicatum was less than when grown on P. perfoliatus. Larvae from another egg-clutch reared on M. spicatum, either from lake or cultivated in aquaria, exhibited reduced growth on the lake plants. P. perfoliatus contained less than 1% and M. spicatum (aquarium or field material) between 5 and 9% phenolic compounds. No differences in nitrogen content of leaves were found, but apical shoot sections of M. spicatum exhibited a significantly higher nitrogen content than P. perfoliatus. Our results indicate that hydrolyzable tannins are responsible for the reduced growth of Acentria when fed with M. spicatum.     

Induction of volatile emissions in maize by different larval instars of Spodoptera littoralis

Maize plants under attack by caterpillars emit a specific blend of volatiles that is highly attractive to parasitic wasps. The release of these signals is induced by elicitors in the caterpillar regurgitant. Studies suggest that plants respond differently to different herbivore species and even to different herbivore stages, thus providing parasitoids and predators with specific signals. We tested if this is the case for different larval instars of the noctuid moth Spodoptera littoralis when they feed on maize plants. Cut maize plants were incubated in diluted regurgitant from second, third, or fifth instar caterpillars. There were no differences in total amount released after these treatments, but there were small differences in the release of the minor compounds phenethyl acetate and -humulene. Regurgitant of all three instars contained the elicitor volicitin. To test the effect of actual feeding by the larvae, potted plants were infested with caterpillars of one of the three instars, and volatiles were collected the following day. The intensity of the emissions was correlated with the number of larvae feeding on a plant, and with the amount of damage inflicted, but was independent of the instar that caused the damage. We also used artificial damage to mimic the manner of feeding of each instar to test the importance of physical aspects of damages for the odor emission. The emission was highly variable, but no differences were found among the different types of damage. In olfactometer tests, Microplitis rufiventris, a parasitoid that can only successfully parasitize second and early third instar S. littoralis, did not differentiate among the odors of maize plants attacked by different instar larvae. The odor analyses as well as the parasitoid's responses indicate that maize odors induced by S. littoralis provide parasitoids with poor information on the larval developmental stage. We discuss the results in the context of variability and lack of specificity in odorous plant signals.     

Ozone Degrades Common Herbivore-Induced Plant Volatiles: Does This Affect Herbivore Prey Location by Predators and Parasitoids?

Inducible terpenes and lipoxygenase pathway products, e.g., green-leaf volatiles (GLVs), are emitted by plants in response to herbivory. They are used by carnivorous arthropods to locate prey. These compounds are highly reactive with atmospheric pollutants. We hypothesized that elevated ozone (O₃) may affect chemical communication between plants and natural enemies of herbivores by degrading signal compounds. In this study, we have used two tritrophic systems (Brassica oleracea–Plutella xylostella–Cotesia plutellae and Phaseolus lunatus–Tetranychus urticae–Phytoseiulus persimilis) to show that exposure of plants to moderately enhanced atmospheric O₃ levels (60 and 120 nl l⁻¹) results in complete degradation of most herbivore-induced terpenes and GLVs, which is congruent with our hypothesis. However, orientation behavior of natural enemies was not disrupted by O₃ exposure in either tritrophic system. Other herbivore-induced volatiles, such as benzyl cyanide, a nitrile in cabbage, and methyl salicylate in lima bean, were not significantly reduced in reactions with O₃. We suggest that more atmospherically stable herbivore-induced volatile compounds can provide important long-distance plant-carnivore signals and may be used by natural enemies of herbivores to orientate in O₃-polluted environments.     

Relation ofSpodoptera eridania choice to tannins and protein oflotus corniculatus

Plant secondary compounds such as tannins may influence herbivore choice. To determine if herbivory was influenced by tannin concentration,Spodoptera eridania larvae were given a choice ofLotus corniculatus plants whose chemical profiles were altered by fertilization. Herbivores chose plants that had been grown with symbiotic nitrogen fixation as their only nitrogen source more often than fertilized plants. Choice was related to protein concentration, but not to tannin concentration.     

Chemical Ecology of the Defense of Two Nymphalid Butterfly Larvae Against Ants

We analyzed the behavioral responses of the ants Camponotus rufipes and Solenopsis geminata towards all instars of Dione junio and Abananote hylonome. We also analyzed ant behavior towards hexane extracts of larvae and extracts of the spines and neck glands of the fifth instars of both species and identified the chemical compounds present. Larvae of both species were repellent to ants from the first instar onward. Later instars survived ant attacks better than earlier instars. The spines and neck glands of the larvae influenced the behavior of C. rufipes. The chemical compounds contained in the hexane extracts of whole first and fifth instars and in the spines and neck glands of fifth instars were principally carboxylic acids and terpenes. Further bioassays confirmed the repellent effect of some of these acids toward ants.