Impact of acidic deposition onEncelia farinosa gray (Compositae: Asteraceae) and feeding preferences ofTrirhabda geminata horn (Coleoptera: Chrysomelidae)

Container grownEncelia farinosa were exposed to three 3-hr episodes of acidic fog (pH 2.5) typical of events in southern California. Adults and larvae of the specialist leaf-feeding herbivore,Trirhabda geminata, preferred to feed on the acidic-treated foliage compared to control fogged (pH 6.3–6.5) foliage. Previous feeding damage on the plants did not affect feeding preference. The acidic-fogged foliage was significantly higher in total nitrogen and soluble protein but not different from control-treated tissue in water content. Stress on native populations of this drought-deciduous shrub caused by atmospheric pollutants may also result in altered feeding ecology of the beetle.     

Stratospheric ozone depletion and plantinsect interactions: Effects of UVB radiation on foliage quality ofCitrus jambhiri forTrichoplusia ni

Projected decreases in stratospheric ozone may result in increases in shortwave ultraviolet (UVB) irradiation at the earth's surface. Furanocoumarins, phototoxic compounds found inCitrus jambhiri foliage, increase in concentration when these plants are grown under enhanced UVB. Survivorship schedules ofTrichoplusia ni (Lepidoptera: Noctuidae) caterpillars reared on plants in the presence and absence of enhanced UVB regimes differ significantly; larvae develop more slowly in early life when reared on plants exposed to increased UVB. This same developmental pattern is observed whenT. ni larvae are reared on artificial diets amended with ecologically appropriate amounts of furanocoumarins. Thus, anthropogenically derived changes in stratospheric ozone and concomitant changes in UV light quality at the earth's surface may influence ecological interactions between insects and their host plants by altering secondary metabolism and hence foliage quality for herbivores.     

Impact of atmospheric pollution on linear furanocoumarin content in celery

In a series of laboratory studies, a single 4-hr acidic fog at pH levels associated with commercial celery (Apium graveolens L.) production near major population centers in California was found to stimulate development of psoralen, bergapten, xanthotoxin, and isopimpinellin within 24 hr and for at least 120 hr after exposure. At 120 hr posttreatment, the concentrations of phototoxin furanocoumarins (psoralen + bergapten + xanthotoxin) increased 540% in the leaves (to 135 g/g fresh weight) and 440% in the petioles (to 55.56 g/g fresh weight) of celery exposed to a pH 2.0 fog as compared to plants exposed to control fogs (pH 6.3–6.5). Concentrations of these compounds in test plants were 7.5 times higher than the amount known to produce contact dermatitis. The nonphototoxic isopimpinellin increased more than threefold in the leaves (to 39.23 g/g fresh weight, 120 hr) and petioles (to 25.88/gmg/g fresh weight) as compared to control plants. In contrast, a single ozone fumigation at 0.20 ppm for 2 hr generally reduced concentrations of phototoxin furanocoumarin in leaves of celery within 24 hr (ozone-treated plants = 37.9, controls = 69.5 g/g fresh weight), but levels of these chemicals in leaves of ozone-fumigated plants increased rapidly and concentrations were not significantly different at 120 hr. Isopimpinellin concentrations in foliage followed a similar trend (at 24 hr, control = 25.11, ozone treated = 10.96/gmg/g fresh weight, no difference at 120 h). In petioles, none of the linear furanocoumarin levels differed significantly at 120 hr posttreatment.     

Effects of Drought Stressed Cotton, Gossypium hirsutum L., on Beet Armyworm, Spodoptera exigua (Hübner) Oviposition, and Larval Feeding Preferences and Growth

The beet armyworm, Spodoptera exigua (Hübner), has been anecdotally reported to oviposit more on drought stressed than on nonstressed cotton plants. Using potted cotton plants in cages, this study demonstrated that beet armyworms deposited 3.3, 4.6, and 2.3 times more (P 0.05) eggs on cotton plants that were grown on 1500, 1000, and 750 ml water/wk, respectively, than on cotton plants grown in well watered (4000 ml water/wk) soil. Third instars, however, showed no preference for stressed cotton foliage over nonstressed foliage. Third instar beet armyworms raised on well watered cotton plants were 1.5, 2.3, and 2.6 times heavier than those reared on cotton grown in the 1500, 1000, and 750 ml water/wk plants (P 0.05), respectively. Physiochemical analyses showed that drought stressed leaves had significantly greater accumulations of free amino acids that are essential for insect growth and development. Soluble protein and soluble carbohydrates were also more abundant in stressed leaves compared to nonstressed leaves. Despite the apparent increase in nutritional quality in drought stressed plants, larval survival was reduced, probably because the limiting factor became water. Greater amounts of cotton leaf area were consumed from drought stressed leaves (P 0.05) than from nonstressed leaves, probably because the larvae had to metabolize greater portions of assimilated energy to supplement body water with metabolic water derived from respiration. The association of greater host plant nutritional quality to oviposition preference, and conversely, to reduced survivorship, is discussed.     

Larval exposure to oviposition deterrents alters subsequent oviposition behavior in generalist,Trichoplusia ni and specialist,Plutella xylostella moths

The present study was undertaken to determine the effects of larval feeding experience on subsequent oviposition behavior of the resulting moths. Larvae of the cabbage looper (Trichoplusia ni, Noctuidae) and the diamondback moth (Plutella xylostella, Plutellidae) were exposed to the phenylpropanoid allelochemical trans-anethole (at 100 ppm fw in artificial diet) or the limonoid allelochemical toosendanin (10 ppm sprayed on cabbage leaves). Both compounds had been shown to deter oviposition in naïve moths in previous choice tests. Moths developing from experienced larvae (both sexes) showed a decrease in oviposition deterrence response when given a choice between control and treated leaves, unlike naïve moths. This phenomenon, analogous to habituation to feeding deterrents in lepidopteran larva, occurred irrespective of duration of feeding on the deterrent compound. We also observed that F₁larvae resulting from experienced moths (previously exposed to toosendanin as larvae) grew as well on toosendanin-treated foliage as on control foliage. In contrast, growth of F₁larvae from naïve moths was significantly impaired by toosendanin. These results demonstrate that host-selection behavior in cabbage looper (a generalist) and diamondback moth (a specialist) may be shaped by feeding experience according to Hopkins' Host Selection Principle in addition to chemical legacy.     

Effects of Water Deficit Stress, Shade, Weed Competition, and Kaolin Particle Film on Selected Foliar Free Amino Acid Accumulations in Cotton, Gossypium hirsutum (L.)

Leaves of cotton plants, Gossypium hirsutum L., stressed by water deficit, reduced daylight, and weed competition, or treated with a kaolin wettable powder formulation were analyzed for levels of 17 free amino acids (FAAs) using reversed-phase high-performance liquid chromatography. Water deficit stress resulted in heightened free proline levels (49.9-fold, P < 0.001) that were correlated with diffusive resistance (seconds per centimeter). Five other FAAs increased, and the amounts of total free essential (for insect growth and development) amino acids and total FAAs also increased (P 0.05). Cotton grown in 50% shade accumulated significantly more free arginine than control plants. In a small-plot weed competition assay, four FAAs increased and three FAAs decreased in association with weed competition, but because free proline levels were not altered and free arginine levels increased, other stresses aside from water deficit, possibly including shading by tall weeds, appear to have caused the changes. In a small-plot kaolin particle film assay, five FAAs were lower in cotton foliage sprayed weekly with kaolin. Because free proline was unaffected and free arginine was lower, it is possible that kaolin's reflectivity heightened light reception. The responses of free proline and arginine to the treatments used in these assays demonstrate that types and degrees of some stresses to cotton can be characterized by accumulations of certain FAAs. The study also demonstrates how some FAA levels can indicate degrees of cotton stress resulting from weed competition and from kaolin particle film application. Porometry and leaf water potential measurements assisted in corroborating some findings of the study.     

Looplure efficacy and electrophysiological responses in three plusiinae species

Source concentration differences of (Z)-7-dodecen-1-ol acetate, or looplure, were evaluated for field trapping efficiency and electrophysiological responses with malePseudoplusia includens (Walker),Trichoplusia ni (Hubner) andRachiplusia ou (Guenné) (Lepidoptera: Noctuidae). Sticky traps baited with 1000 g of the lure captured a significantly greater (P < 0.05) number of maleP. includens andT. ni than any other concentration;R. ou males were caught at a greater rate in traps baited with 100 g of looplure, significantly more (P < 0.05) than with 1000 g. Electroantennogram (EAG) studies demonstrated that antennae of maleP. includens have a lower response threshold to looplure than eitherT. ni orR. ou antennae, the latter demonstrating the highest significant threshold of response. No differences in the stimulus-response functions of the three species were detected.Lepidoptera: Noctuidae.     

Plant virus-induced changes in aphid population development and temporal fluctuations in plant nutrients

Cucurbita pepo plants were infected with zucchini yellow mosaic virus or maintained noninfected.Aphis gossypii, which transmits the virus, lived longer and produced more offspring on infected than on noninfected plants. On infected plants, the intrinsic rate of natural increase forA. gossypii increased with time after inoculation. In a similar experiment, concentrations of phloem sap nutrients, including free amino acids, total protein, and sugars from infected and noninfected plants were compared for 37 days after inoculation. Significant differences in levels of individual amino acids from phloem exudate between infected and noninfected plants were found, yet the concentration of total amino acids was not substantially different between infected and noninfected plants. Beginning four days after inoculation, the total protein content of phloem exudate generally was lower in infected plants than noninfected plants. Likewise, the total sugar content of phloem exudate from infected plants was lower than that of noninfected plants beginning nine days after inoculation. In contrast with the results from analyses of phloem exudate, foliage from infected plants had higher levels of almost all amino acids than noninfected foliage beginning nine days after inoculation. Concentrations of individual and total amino acids in infected foliage increased throughout the experimental period. Although no temporal effects were observed in the foliage sugar content for either individual or total sugars, starch content decreased with time in infected plants, while in noninfected plants, starch content remained level.     

Defensive Role of Tomato Polyphenol Oxidases against Cotton Bollworm (<Emphasis Type="Italic">Helicoverpa armigera</Emphasis>) and Beet Armyworm (<Emphasis Type="Italic">Spodoptera exigua</Emphasis>)

Tomato (Solanum lycopersicum) polyphenol oxidases (PPOs), enzymes that oxidize phenolics to quinones, have been implicated in plant resistance to insects. The role of PPO in resistance to cotton bollworm [Helicoverpa armigera (Hübner)] and beet armyworm [Spodoptera exigua (Hübner)] (Lepidoptera: Noctuidae) was evaluated. Consumption, weight gains, and mortality of larvae feeding on foliage of transgenic tomato lines overexpressing PPO (OP lines) and of larvae feeding on foliage of transgenic tomato lines with suppressed PPO (SP lines) were compared with consumption, weight gains, and mortality of larvae feeding on non-transformed (NT) plants. Increases in foliage consumption and weight gains were observed for cotton bollworms feeding on leaves of SP plants compared to NT and OP plants. PPO activity was negatively correlated with both weight gains and foliar consumption of cotton bollworm, substantiating the defensive role of PPO against this insect. Similarly, beet armyworm consumed less foliage (both young and old leaves) from OP plants than SP plants. Larvae feeding on OP leaves generally exhibited lower weight gains than those feeding on SP leaves. These results indicate that tomato PPO plays a role in resistance to both cotton bollworm and beet armyworm.     

Ozone-induced changes in host-plant suitability: Interactions ofKeiferia lycopersicella andLycopersicon esculentum

Tomato pinworms,Keiferia lycopersicella (Walsingham), survived better and developed faster on tomato plants,Lycopersicon esculentum Mill., damaged by ozone than on plants not subjected to ozone fumigation. Other measures of fitness, including survival during pupation, sex ratio of adults, female longevity, and fecundity, were not affected. Analyses of ozonated foliage at zero, two, and seven days following fumigation demonstrated a transient but significant increase (18–24%) in soluble protein concentration. Although the concentration of the total free amino acids in ozonated foliage did not increase significantly, significant changes were observed in at least 10 specific amino acids, some of which are critical for either insect development or the production of plant defensive chemicals. A reduction in total nitrogen in ozonated foliage at seven days postfumigation indicated that nitrogen was being translocated to other portions of the plant. The implications of increases in assimilable forms of nitrogen in ozonated foliage, which lead to improved host-plant suitability for insect herbivores, are discussed both in relation to some current ecological theories and in regard to pest-management strategies.     

Induced resistance in soybean toHelicoverpa zea: Role of plant protein quality

Resistance in soybean toHelicoverpa zea is comprised of both constitutive and inducible factors. In this study, we investigated the induction of resistance byH. zea in both greenhouse and field studies. In a greenhouse experiment, fourth-instarH. zea growth rates were reduced by 39% after 24 hr feeding and by 27% after 48 hr when larvae fed on previously wounded V3 foliage (cv. Forrest) compared with undamaged foliage. In a field study, the weight gain by larvae was more than 52% greater when larvae fed for 72 hr on undamaged R2/R3 soybean plants (cv. Braxton) compared to those that fed on previously wounded plants. A significant component of the induced resistance is due to a decline in the nutritional quality of foliar protein following foliar damage byH. zea. Foliar protein was extracted from damaged and undamaged foliage and incorporated into artificial diets. Larval growth was reduced 26% after four days and 49% after seven days on diets containing protein from damaged plants compared to larvae feeding on foliar protein from undamaged plants. Chemical analyses of protein quality also indicated a decline in quality in damaged plants compared to unwounded plants. Increases in lipoxygenase activity (53%), lipid peroxidation products (20%), and trypsin inhibitor content (34%) were observed in protein from wounded plants. Moreover, a 5.9% loss in free amines and 19% loss in total thiols occurred in protein from wounded plants. Larval feeding causes a significant increase in foliar lipoxygenase activity that varied among genotypes. Lipoxygenase isozymes were measured at pH 5.5, pH 7.0, and pH 8.5 in V3 stage plants of Forrest, Hark, D75-1069, and PI 417061 genotypes. Lipoxygenase activity in each genotype was significantly increased after 72 hr of larval feeding at each pH level tested, with the exception of lipoxygenase isozymes at pH 5.5 in genotype PI 417061. Larval feeding on R2/R3 stage plants (field-grown cv. Braxton) for six days also increased foliar lipoxygenase activity.     

Genetic variation and relationships of constitutive and herbivore-induced glucosinolates,trypsin inhibitors,and herbivore resistance in Brassica rapa

We examined genetic variation in inducibility and in constitutive and herbivore-induced levels of glucosinolates, trypsin inhibitors, and resistance to herbivory in families of Brassica rapa originating from a wild population. We also examined phenotypic and genetic correlations among absolute levels of these traits in control and induced plants. We grew seedlings of 10 half-sib families in pairs in pots, and exposed one plant per pair to folivory by Trichoplusia ni larvae. Two days later, we sampled all plants for total glucosinolate and trypsin inhibitor levels and examined the preference and consumption by T. ni larvae of previously damaged (induced) and undamaged (control) plants. There was no significant variation among sire families in the induction of glucosinolates or trypsin inhibitors by T. ni feeding. Total glucosinolate levels in either control or induced plants did not vary by family. In contrast, trypsin inhibitor levels in both control and induced plants varied significantly by family. Trichoplusia ni fed less on induced plants than on control plants in the bioassay, but neither the induction of resistance by prior T. ni feeding nor absolute levels of damage done to control and induced plants varied significantly by sire family. Temporal blocking strongly affected trypsin inhibitor levels and the response of some families in the bioassays. There were no significant phenotypic or genetic correlations of levels of glucosinolates or trypsin inhibitors with each other or with damage in either control or induced plants. Overall, these results suggest that in the B. rapa population that we studied, both total glucosinolate content and biological resistance to herbivory by T. ni was nonvariable and almost universally inducible by prior T. ni feeding. In contrast, control and induced levels of trypsin inhibitors varied genetically and have the capacity to respond to future selection imposed by herbivores. However, the role of these defenses in constitutive or induced resistance to T. ni in this species remains unclear.     

Factors Affecting Volatile Emissions of Intact Potato Plants, Solanum tuberosum: Variability of Quantities and Stability of Ratios

The quantity, ratios, diurnal rhythm, and correlation with foliage weight of volatile chemicals emitted by young and mature intact potato plants were determined during the fourth (morning), eighth (noon) and fourteenth (afternoon) hour of the photophase. The major compounds released by young and mature intact potato plants, Solanum tuberosum, during the photophase, were the sesquiterpene hydrocarbons -caryophyllene, (E)--farnesene, (Z,Z)--farnesene, germacrene-D, -bisabolene, and an unknown compound A. The quantity of the major volatile chemicals emitted was subject to diurnal rhythm. In young potatoes, all major compounds except unknown A showed a steady increase during the photophase, with afternoon production significantly higher than that in the morning. In mature potatoes, all compounds, including unknown A, were significantly higher during the afternoon when compared to morning. Although the variability in quantity of volatile chemicals released between individual plants was very high, the ratios were stable between the sets of replicates. The correlation of foliage weight and emission of the volatile compounds was affected by the developmental stage of the plant and the time of the day. There was a positive correlation between foliage weight and production of volatile chemicals that was strongly evident in mature potato plants, and much less evident in young plants during morning and afternoon. No positive correlation between foliage weight and production of volatile chemicals was observed during noon for either age tested. The factors affecting the volatile emissions of intact potato plants are discussed.     

Effects of host plant,Gossypium hirsutum L., on sexual attraction of cabbage looper moths,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae)

Unmated female or male cabbage looper moths,Trichoplusia ni (Hübner), were attracted more often in a flight tunnel to a cage with moths of the opposite sex and a bouquet of cotton foliage. Increased sexual attractiveness of females with plants may be a result of stimulation of pheromone release in response to plant odor, since more males were attracted when odor of cotton foliage was passed over females than when odor of females was passed over cotton foliage before venting into the flight tunnel. Increased sexual attractiveness of males with plants is due in part to host odor enhancement of female attraction to male pheromone, since more females were attracted to synthetic male pheromone (a blend of enantiomers of linalool and isomers of cresol) and a cotton leaf extract than were attracted to male pheromone alone. A short synthesis procedure was developed for (S)-(+)-linalool, the major component of the male sex pheromone, isolated from hair pencils, used in these tests.     

Behavioral and physiological responses of cabbage looper,Trichoplusia ni (Hübner), to steam distillates from resistant versus susceptible soybean plants

Soybean plant volatiles, extracted as steam distillates, significantly affected the behavior and biology of the cabbage looper,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). Distillates from the susceptible Davis variety attractedT. ni larvae and female adults, whereas those from resistant PI 227687 plants repelled them. When mixed in an artificial diet, steam distillates from PI 227687 plants caused mortality of first-instar larvae. Adults emerging from pupae topically treated with 5 g of such PI 227687 extractable showed developmental abnormalities. Larval feeding was significantly less on Davis leaves treated with PI 227687 volatiles as compared to solvent (acetone) or such Davis extractables. However, Davis volatiles on PI 227687 leaves did not increase larval feeding. HPLC analyses of steam distillates from susceptible Davis versus resistant PI 227687 indicated differences.     

Influence of cabbage proteinase inhibitorsin situ on the growth of larvalTrichoplusia ni andPieris rapae

Trypsin and chymotrypsin inhibitors are proteins that are developmentally regulated in foliage of cabbage plants, appearing at high concentrations in young foliage on mature plants. This temporal and spacial regulation of foliar proteinase inhibitors is synchronized with the appearance and distribution of foliar feeding Lepidoptera. When insects were allowed to select their feeding sites, larvalPieris rapae fed on the young foliage of cabbage plants, while larvalTrichoplusia ni fed on the mature foliage on cabbage plants. LarvalP. rapae that fed on mature plants were significantly smaller than larvae feeding on young plants, while there was no significant difference between larvalT. ni feeding on mature plants and those feeding on young plants. Thus, there was a significant inverse correlation between the level of proteinase inhibitory activity in cabbage foliage and larval growth. WhenP. rapae andT. ni were provided with an artificial diet containing total protein (including significant levels of proteinase inhibitors) that was extracted from cabbage foliage, there was a significant reduction in growth and development of both species of Lepidoptera.     

A flavonoid glucoside,phellamurin, regulates differential oviposition on a rutaceous plant,Phellodendron amurense,by two sympatric swallowtail butterflies,Papilio protenor andP. xuthus: The front line of a coevolutionary arms race?

We studied the chemical basis for the differential acceptance of a rutaceous plant.Phellodendron amurense, by ovipositing females of two sympatricPapilio butterflies,P. protenor andP. xuthus, that have a very similar host range.P. amurense, on which larvae of both species perform well, was rejected byP. protenor females but was marginally accepted byP. xuthus, even though water-soluble fraction of this plant elicited significant ovipositional responses from the two species. A prenylated dihydroflavonol glucoside, 3,5,7,4-tetrahydroxy-8-(3-methylbut-2-enyl)flavanone-7-O--glucoside (phellamurin), was identified as a dominant active substance that deters oviposition.P. protenor responded highly sensitively to phellamurin, whereasP. xuthus was less susceptible and was affected conspicuously only at higher concentrations than that found in living plants, thereby accounting for their differential responses toP. amurense. InP. protenor, the deterrent effect of phellamurin was considered to outweigh the activity of coexisting stimulant(s) at the concentrations actually present in the foliage, resulting in avoidance of this plant. The phellamurin content in the foliage amounted to as much as 1.8% of the fresh weight, which is far higher than the average levels of flavonoids present in other major host plants ofPapilio. The dose-response experiments demonstrated that unacceptability ofP. amurense forP. protenor was attributable largely to such a high concentration of phellamurin. These results appear to provide information on possible coevolutionary interactions between herbivores and plants and also on the potential for shifts in host affiliation.     

Systemic Induction of Allelochemicals in Glanded and Glandless Isogenic Cotton by Spodoptera exigua Feeding

Induction of systemic resistance to feeding of beet armyworm, Spodoptera exigua, was investigated in two isogenic lines of Stoneville 213 cotton, Gossypium hirsutum, that differed in the presence of pigment glands. In laboratory bioassays, larvae strongly preferred to feed on glandless cotton plants when presented a choice between undamaged terminal leaves of undamaged glanded and glandless plants. Feeding damage inflicted by S. exigua larvae on the two oldest leaves of glanded plants seven days prior to feeding bioassays caused larvae to prefer by 33-fold the undamaged terminal foliage from undamaged plants compared to that from damaged plants. Feeding damage on glandless plants caused only a 2.6-fold greater preference for terminal foliage from undamaged plants over foliage from previously damaged plants. Extracts of terminal foliage from glanded cotton damaged seven days earlier had significantly greater quantities of terpenoid aldehydes (hemigossypolone, gossypol, and heliocides) than did foliage from undamaged glanded plants. Terpenoid aldehydes were undetectable in extracts of both undamaged and previously damaged glandless plants. The profile of volatile compounds collected from the headspace of mechanically damaged terminal leaves of undamaged glanded and glandless plants differed. Both cotton isolines released large quantities of lipoxygenase products (hexenyl alcohols, acetates, and butyrates), but glandless plants released only small amounts of mono- and sesquiterpenes compared to glanded plants. Glandless plants damaged seven days prior to volatile collection released significantly greater quantities of lipoxygenase products, -ocimene, and - and -farnesene than did undamaged glandless plants. Previously damaged glanded plants released significantly greater quantities of all mono- and sesquiterpenes and hexenyl acetates and butyrates, but not alcohols. The relative importance of volatile compounds versus terpenoid aldehydes in induced feeding deterrence in cotton to S. exigua larvae is still unclear.     

Leaf Ontogeny Influences Leaf Phenolics and the Efficacy of Genetically Expressed Bacillus thuringiensis cry1A(a) d-Endotoxin in Hybrid Poplar Against Gypsy Moth

We tested the hypothesis that ontogenetic variation in leaf chemistry could affect the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin, and thus provide spatial variation in (1) foliage protection and (2) selective pressures that could delay the resistance of folivores. Our model consisted of clonal hybrid Populus plants (NC5339). Consumption of foliage and relative growth rates of gypsy moth, Lymantria dispar (L.) increased, and phenolic glycoside concentrations decreased, as leaves from transformed plants containing the cry1A(a) d-endotoxin and nontransformed plants matured from leaf plastochron index (LPI) 1–6. Feeding and growth rates were negatively correlated with phenolic glycosides in both transformed and nontransformed foliage. The presence of the B. thuringiensis d-endotoxin was at most, additive to the effect of the phenolic glycosides. Feeding and growth rates were positively correlated with condensed tannins in transformed foliage, but there was no relationship with condensed tannins in nontransformed foliage. The results indicate that the presence of foliar allelochemicals of poplar can enhance the effectiveness of genetically expressed B. thuringiensis d-endotoxin against gypsy moth larvae. However, the spatial variation in gypsy moth performance in response to the combination of foliar allelochemicals and d-endotoxin was not greater than the effect of ontogenetic variation in foliar allelochemicals alone. These results suggest that for this important pest, foliage protection may be obtained without genetically engineered defenses, and instead, by relying on ontogenetic and clonal variation in allelochemicals. The benefits of combining novel resistance mechanisms with natural ones will depend upon the specific folivore's adaptation to natural resistance mechanisms, such as allelochemicals. Moreover, some of the greatest benefits from transgenic resistance may arise from the need to protect trees from multiple pests, some of which may not be deterred by, or may even prefer, allelochemicals that confer protection from a few species.     

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.