Robert R. Farrar

2-Undecanone, a constituent of the glandular trichomes of Lycopersicon hirsutum f. glabratum: Effects on Heliothis zea and Manduca sexta growth and survival

The effects of 2‐undecanone, a compound found in the glandular trichomes of the wild tomato, Lycopersicon hirsutum f. glabratum C. H. Mull, PI 134417, on the larvae of Heliothis zea (Boddie) and Manduca sexta (L.) were studied by rearing the larvae on artificial diets containing this chemical. 2‐Undecanone increased larval mortality of H. zea in the first 48 h when combined with 2‐tridecanone, but not alone, and caused deformity and mortality of H. zea pupae both alone and in combination with 2‐tridecanone. 2‐Undecanone had no effect on M. sexta larvae or pupae. Potential implications of these findings for insect pest management are discussed.

Growth, food consumption and mortality of Heliothis zea larvae on foliage of the wild tomato Lycopersicon hirsutum f. glabratum and the cultivated tomato, L. esculentum

Larvae of Heliothis zea (Boddie) were fed foliage of the resistant wild tomato Lycopersicon hirsutum f. glabratum C. H. Mull (PI 134417) and susceptible L. esculentum (cultivar “Walter”), either with the glandular trichomes removed or with the trichomes intact. Response variables measured included larval mortality, larval weight, consumption rate (CR), and efficiency of conversion of ingested material (ECI). Resistant foliage was found to contain factors in both the trichomes and leaf lamellae which increased larval mortality, reduced larval weight, reduced CR, and, except in second instars, reduced ECI. Susceptible foliage also contained trichome‐based factors which increased larval mortality and decreased weight, as well as CR of second instars and ECI of fifth instars. Implications of these findings for breeding resistant tomato cultivars are discussed.

Behavioral response ofTrichogramma pretiosum riley andTelenomus sphingis (Ashmead) to trichome/methyl ketone mediated resistance in tomato

Effects of methyl ketone (2-tridecanone and 2-undecanone)/glandular trichome-based resistance to insects ofLycopersicon hirsutum f.glabratum C.H. Mull, PI 134417, on the behavioral responses ofTrichogramma pretiosum Riley andTelenomus sphingis (Ashmead) were observed in the laboratory. ForT. pretiosum, these effects included (1) longer time required by the wasps to cross a leaf disk (diam. 16.3 mm), (2) higher percentage of wasps initiating flight from disks before reaching the edge, and (3) entrapment of wasps in trichome exudates. In tomato genotypes with varying densities of type VI glandular trichomes (3.1–9.2/mm2) but with no methyl ketones in the trichome tips, no such adverse effects were observed. The time taken to cross a disk or initiate flight byT. sphingis, a larger wasp thanT. pretiosum, was not significantly affected on 16.3-mm leaf disks, although the percentage ofT. sphingis initiating flight was directly correlated with trichome density among lines with no ketones. When placed on whole leaflets of plant lines with or without methyl ketones,T. sphingis was entangled by trichome exudates. However, unlikeT. pretiosum, T. sphingis was eventually able to free itself from entanglement. Landing rates byT. sphingis on PI 134417 foliage contained in dialysis tubes were also reduced. Data indicate that suppression of egg parasitism byT. sphingis on resistant foliage is due to both repellent action of its foliar volatiles and reduced searching rates by the parasitoids. Results indicate that a significant portion of the reduction of egg parasitism byT. pretiosum andT. sphingis is attributable to the effects of 2-tridecanone and/or 2-undecanone present in the tips of type VI glandular trichomes on PI 134417 foliage, although the trichomes also adversely affect the wasps even in plant lines without ketones.

Field evaluation of insect resistance in a wild tomato and its effects on insect parasitoids

Populations of Helicoverpa (= Heliothis) zea (Boddie), Heliothis virescens (F.), Manduca sexta (L.) and M. quinquemaculata (Haw.) and their egg and larval parasitoids were sampled in field plots of the: insect‐resistant wild tomato, Lycopersicon hirsutum f. glabratum C. H. Mull, accession PI 134417; susceptible commercial tomato cultivar ‘Better Boy’ F1 hybrid; and selected, moderately resistant backcross genotype. Densities of H. zea and H. virescens eggs and small larvae were higher on resistant genotypes than on susceptible genotypes, but densities of large larvae were similar on all genotypes. Densities of Manduca spp. larvae were too low to permit similar analyses of the effects of plant genotype. Rates of egg parasitism by Trichogramma spp. and Telenomus sphingis (Ashmead) were reduced on insect‐resistant genotypes. Rates of parasitism by the larval parasitoids Campoletis sonorensis (Cameron) and Cotesia congregata (Say) were reduced on resistant genotypes. No consistent effects on parasitism rates by Cotesia marginiventris (Cresson) were observed and parasitism rates by Cardiochiles nigriceps Viereck were unaffected.

Host Plant Effects on the Activity of Selected Nuclear Polyhedrosis Viruses Against the Corn Earworm and Beet Armyworm (Lepidoptera: Noctuidae)

Abstract The activity of the nuclear polyhedrosis virus (NPV) of the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), against the beet armyworm, Spodoptera exigua (Hübner), was greatest when the virus was fed to larvae on foliage of tomato, Lycopersicon esculentum Mill., least on cotton, Gossypium hirsutum (L.), and intermediate on collard, Brassica oleracea L. Activity of AfMNPV against the corn earworm, Helicoverpa zea (Boddie), was greatest on corn, Zea mays L., least on cotton, and intermediate on bean, Phaseolus vulgaris L. Survival time (days between the start of the test and death) of larvae that were killed by virus was usually lower on treatments on which rates of mortality were higher, but these differences were usually small (≤1 d). Effects of host plants on viral activity were not related closely to their effects on larval feeding rates. Effects of host plants on viral activity were also not specific to AfMNPV; cotton and collard affected AfMNPV and the homologous NPV of the beet armyworm to similar degrees. Similar results were found for AfMNPV and the homologous NPV of the corn earworm on cotton and bean. Levels of control provided by these viruses may thus be higher on tomato or corn than on cotton, and intermediate on collard or bean.

Interaction of fertilizer regime with host-plant resistance in tomato

The effect of fertilizer regime on trichome‐ and lamellar‐based resistance in the wild tomato species, Lycopersicon hirsutum f. glabratum C. H. Mull accession PI 134417, to three insect pests of tomato, the tobacco hornworm, Manduca sexta (L.), the Colorado potato beetle, Leptinotarsa decemlineata (Say), and the tomato fruitworm, Heliocoverpa zea (Boddie), was examined. Increasing the rate at which NPK fertilizer was applied, from 1.8 to 19.6 g/plant/week, reduced the trichome‐based resistance of PI 134417 to M. sexta and L. decemlineata by lowering both the density of type VI (sensu Luckwill, 1943) glandular trichomes and the amount of 2‐tridecanone contained in the tips of these trichomes. 2‐Tridecanone is a toxic methyl‐ketone responsible for glandular trichome‐mediated resistance in PI 134417 to M. sexta and L. decemlineata. A similar increase in the application rate of NPK fertilizer reduced the lamellar‐based resistance of PI 134417 to L. decemlineata and H. zea. The meachanisms for this reduction of resistance are unknown, but may be related to improved nutritional quality of hosts at higher fertilizer regimes.

Interaction of Manduca sexta resistance in tomato with insect predators of Helicoverpa zea

Resistance in accession PI 134417 of Lycopersicon hirsutum f. glabratum to Manduca sexta L. results from the presence of the methyl ketones 2‐tridecanone and 2‐undecanone in the type VI trichome glands on foliage of these plants. Short (24 h) and long term (neonate to adult) laboratory experiments using M. sexta‐resistant and susceptible foliage and methyl ketone treated filter paper disks were conducted to evaluate the direct (plant‐mediated) and indirect (prey‐mediated) effects of this resistance on two predators of Helicoverpa zea eggs, Coleomegilla maculata (DeGeer) and Geocoris punctipes (Say). Direct effects of resistance were manifest as reduced egg consumption and increased mortality for both predators. Indirect effects were manifest as reduced egg consumption by G. punctipes, but were not observed for C. maculata. Results of experiments using methyl ketone‐treated filter paper disks instead of foliage were similar.

Inhibition of Telenomus sphingis an egg parasitoid of Manduca spp. by trichome/2‐tridecanone‐based host plant resistance in tomato

The resistance of accession PI 134417 of the wild tomato Lycopersicon hirsutum f. glabratum C. H. Mull to Manduca sexta (L.) (Lepidoptera: Spingidae) and Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is conditioned by the high densities of 2‐tridecanone‐containing, glandular trichomes associated with the foliage. In laboratory experiments, rates of parasitism of M. sexta eggs by Telenomus sphingis (Ashmead) (Hymenoptera: Scelionidae) were lower among eggs on PI 134417 foliage than among eggs on foliage of the cultivated tomato L. esculentum Mill. (cv. Better Boy). The latter is characterized by a significantly lower density of type VI glandular trichomes than PI 134417 and an absence of 2‐tridecanone. Parasitism by T. sphingis was also reduced among eggs on foliage of the F1 hybrid between PI 134417 and L. esculentum. The hybrid foliage lacks 2‐tridecanone but has a density of type VI glandular trichomes that is intermediate between those of PI 134417 and L. esculentum, indicating that elevated densities of type VI glandular trichomes adversely affect T. sphingis. This conclusion was further substantiated by the finding that there were no differences among plant lines in the levels of parasitism of M. sexta eggs when the eggs were on foliage that had been divested of glandular trichomes.

2-Undecanone, a pupal mortality factor in Heliothis zea: sensitive larval stage and in planta activity in Lycopersicon hirsutum f. glabratum

2‐Undecanone, a compound found in the tips of the Type VI glandular trichomes of the wild tomato species Lycopersicon hirsutum f. glabratum C. H. Mull (accession PI 134417), when incorporated in artificial diet, was previously shown to cause pupal deformity and mortality among Heliothis zea (Boddie). In the present study, the developmental stage of H zea sensitive to the effects of dietary 2‐undecanone was determined by rearing larvae through the fourth instar on diet with or without 2‐undecanone, then transferring them to new diet either with or without 2‐undecanone. Dietary levels of 2‐undecanone (0.055% wet wt) were representative of concentrations found in PI 134417 foliage. Ingestion of 2‐undecanone during the fifth instar was both necessary and sufficient to cause pupal mortality. Rearing fifth instar H. zea on PI 134417 foliage with glandular trichomes intact (2‐undecanone present at 0.084 ± 0.026% wt wt) or with the trichomes, and hence 2‐undecanone, removed indicated that these effects occur in planta. Potential implications of these findings for using 2‐undecanone‐mediated resistance for insect pest management are discussed.

Mortality and inhibition ofHelicoverpa zea Egg parasitism rates byTrichogramma in relation to trichome/methyl ketone-mediated insect resistance ofLycopersicon hirsutum f. glabratum, accession PI 134417

The glandular trichome/methyl ketone-mediated insect resistance of the wild tomato,Lycopersicon hirsutum f. glabratum C.H. Mull, accession PI 134417, toManduca sexta (L.) andLeptinotarsa decemlineata (Say) was shown to affect adverselyTrichogramma pretiosum Riley. AdultT. pretiosum were killed by direct contact with PI 134417 foliage and by exposure to its volatiles. This effect was greatly reduced or eliminated by removing the exudate of the glandular trichomes from the foliage. 2-Tridecanone, a principal consituent of the foliar glandular trichomes of PI 134417, was toxic to adultT. pretiosum at concentrations similar to those associated with PI 134417 foliage. Incubation of parasitizedHelicoverpa (=Heliothis) zea (Boddie) eggs on PI 134417 foliage or 2-tridecanone-treated filter paper significantly reduced the proportion of eggs producing adult parasitoids. Similarly, incubation of parasitizedH. zea eggs on filter paper treated with 2-undecanone, another constituent of the glandular trichomes of PI 134417, caused an increase in the percentage of host eggs containing dead parasitoid pupae.