Pseudaletia Unipuncta Research Articles

Effects of Time After Last Herbivory on the Attraction of Corn Plants Infested with Common Arymworms to a Parasitic Wasp Cotesia kariyai

Females of the gregarious endoparasitoid Cotesia kariyai were attracted to a blend of volatiles released from corn plants infested with larvae of their host, the common armyworm (Mythimna separata). We investigated the effects of time after the last infestation (1-168 h) on the attractiveness of corn plants infested by host larvae by using a wind tunnel under laboratory conditions. Immediately after the removal of the larvae, parasitoids were attracted more to plants that had been infested with the larvae than to intact plants (control). This attractiveness gradually decreased with time after the last infestation. The attractiveness of the infested plants was significantly higher than that of intact plants when the time after the last infestation was within 1 day. Fifteen herbivore-induced volatiles were recorded in the headspace of infested corn plants irrespective of time. The amounts of some compounds including (Z)-3-hexen-1-yl acetate, which have already been reported to attract C. kariyai, correlated with the attractiveness. The ecological meaning of the duration of production of C. kariyai attractants is discussed.

Does Modification of Tall Fescue Leaf Texture and Forage Nutritive Value for Improved Livestock Performance Increase Suitability for a Grass‐feeding Caterpillar?

Grass breeders are developing new forage‐type tall fescue [Schedonorus arundinaceus (Schreb.) Dumort = Lolium arundinaceum (Schreb.) Darbysh., formerly known as Festuca arundinacea Schreb.] cultivars with smoother texture, improved nutritive value, and reduced fiber for improved livestock performance. We tested if such grasses are also more susceptible to a grass‐feeding caterpillar. True armyworms, Pseudaletia unipuncta (Haworth), were reared from first instar to adult on grass clippings from thirteen fescue cultivars or accessions differing in texture (smooth vs. standard), ecotype (northern European vs. Mediterranean), use (pasture vs. turf‐type), or provenance to clarify how modifying the texture (edge spines, trichomes, or cellulose margin), thickness, tissue strength, and nutritive value (dry matter, fiber, ash, or N) of pasture grasses will affect their resistance. We also studied feeding site initiation and development of first instars on intact leaf blades when prevented from exploiting a cut leaf edge. Larvae performed equally well across all groups when reared with grass clippings, despite variation in leaf texture and nutritive value. On intact blades, however, leaf thickness and tissue strength were correlated with reduced feeding site initiation and larval development. Gregarious and window feeding may allow more efficient exploitation of common feeding sites on tougher leaves. True armyworm is adapted to feed on a range of structurally‐diverse grasses, so increased use of forage‐type tall fescue cultivars with smoother texture or reduced fiber is unlikely to worsen its damage to pastures.

In vitro growth of microsporidia Anncaliia algerae in cell lines from warm water fish

Anncaliia algerae is an aquatic microsporidium that most commonly infects mosquitoes but can be grown on the rabbit kidney cell line, RK-13. Spores were purified from RK-13 cultures and added to cell lines from warm water fish and from an insect. The cell lines were GFSK-S1 and GFB3C-W1 from goldfish skin and brain respectively, ZEB2J from zebrafish embryos, FHMT-W1 from fathead minnow testis, and Sf9 from ovaries of a fall armyworm moth. All cultures were maintained at 27°C. Infection was judged to have taken place by the appearance of sporonts and/or spores in cells and occurred in all cell lines. Spores were also isolated from ZEB2J cultures and used to successfully infect new cultures of ZEB2J, RK-13 and Sf9. These results suggest that cells of a wide range of vertebrates support A. algerae growth in vitro and fish cells can produce spores infectious to cells of mammals, fish, and insects.

Biological activity of essential oils from seven Azorean plants against Pseudaletia unipuncta (Lepidoptera: Noctuidae)

AbstractTen essential oils from seven Azorean plant species were evaluated for their insecticidal, ovicidal, feeding‐deterrence and growth inhibition activities against Pseudaletia unipuncta. The oils of Laurus azorica (leaves), and Juniperus brevifolia (leaves) showed strong moderate insecticidal effect on fourth‐instar larvae causing 93.3% and 46.7% mortality, respectively. Juniperus brevifolia (leaves), L. azorica (leaves), Persea indica (leaves), Hedychium gardnerianum (leaves) and Pittosporum undulatum (fruits and leaves) significantly affected the hatching of P. unipuncta eggs (<8% eclosions). Five oils showed significant feeding deterrent activities (L. azorica, 92.4%, J. brevifolia, 93.6%, P. undulatum leaves, 95.5% and fruits, 83.8% and H. gardnerianum, 88.2%). All of the essential oils tested, significantly inhibited the larval growth after 5 days of feeding on the treated diet. Essential oils from L. azorica and J. brevifolia were the most potent growth inhibitors among the oils tested, producing a decrease in the initial larva weight (−14.8 and −14.5 mg, respectively). Our results indicate that L. azorica (leaves), J. brevifolia (leaves), P. indica (leaves), H. gardnerianum (leaves), and P. undulatum (leaves and fruits) can be exploited for the development of bioactive compounds as a new source of agrochemicals. Further emphasis on isolation and identification of active constituents can be useful to develop new environment‐friendly insect control agents.

Bioavailability of heavy metals and apoptotic effects on the midgut cells of Pseudaletia unipuncta (Lepidoptera: Noctuidae) inhabiting volcanic environments

In Sao Miguel Island (Azores, Portugal) volcanic activity is manifested by the occurrence of soil degassing, hydrothermal vents and gas emissions on geothermal grounds; consequently, organisms living in such volcanic environments are chronically exposed to metals, as particles or associated with gases, being therefore potential sentinels of the effects derived from such exposure. Concentrations of seven trace elements (Ca, Cd, Cu, Mg, Mn, Pb, Rb, and Zn) were measured in soil, grass leaves (Lolium perenne), and larvae of Pseudaletia unipuncta from sites exposed and non-exposed to volcanic activity. Morphometry and semi-quantification of apoptotic nuclei (TUNEL test) of the midgut epithelial cells of P. unipuncta larvae were also analyzed. Soils and grass not exposed to volcanic activity showed higher levels for most of the analyzed elements with the exception of Rb. The higher levels of Cd, Zn and Mg in soils and grass from the site with no volcanic activity are probably related to the severe artificial fertilization in the studied pastures. Contrarily to soil and grass, larvae from the site with volcanic activity showed higher levels of Cu, Mn, Rb and Zn, suggesting that the volcanic environment (characterized by a lower pH, etc.) could contribute to an increase in the bioavailability of these elements to the larvae. Apoptosis was significantly higher in cells from digestive epithelium of larvae exposed to volcanic activity, probably as a cellular response and adaptation of these organisms when inhabiting active volcanic environments.

In vivo characterization of two granuloviruses in larvae of Mythimna separata (Lepidoptera: Noctuidae)

The pathogenicity of two granuloviruses (GVs), Xestia c-nigrum GV (XecnGV) and Pseudaletia unipuncta GV (PsunGV), was examined in Mythimna separata. Partial sequencing of the genome of PsunGV indicated that it is related closely to XecnGV, but considered to be a different species. PsunGV and XecnGV showed similar pathogenicity in terms of dose-mortality response and pattern of host mass changes following infection. Both GVs killed infected larvae in 2-3 weeks. Temporal changes in the concentrations of GV-specific DNA in the larval haemolymph were measured by using a real-time quantitative PCR. Viral DNA concentration increased quickly and reached a plateau at 60-72 h post-inoculation. Rates of budded virus (BV) production of each GV were estimated on the basis of viral DNA concentrations by a modified Gompertz model. The slopes of the estimated BV growth curves of both XecnGV and PsunGV in M. separata larvae were equivalent to that of Mamestra brassicae nucleopolyhedrovirus (NPV) in its original host, reported in our previous study. This suggested that BV production is not a major factor in the slower killing speed of GVs in comparison to NPVs. The GV-infected larvae survived for an additional 10 days or more after reaching a maximum level of BV concentration, and kept growing without pupation. These findings also suggested that the GVs have a unique mechanism to regulate the growth of host larvae.

Insecticidal Activities of Commercial Rosemary Oils (Rosmarinus officinalis.) Against Larvae of Pseudaletia unipuncta. and Trichoplusia ni. in Relation to Their Chemical Compositions

Rosemary [Rosmarinus officinalis. L. (Lamiaceae)] essential oil has insecticidal properties and is the active ingredient in a number of commercial insecticides. Like other plant essential oils, the chemical composition of rosemary oil can vary based on genotype, geography, climate, and method of preparation. This study explored the relationship between chemical composition and insecticidal activity of 10 commercial samples of rosemary oil, based on laboratory bioassays with two agricultural pests, the armyworm Pseudaletia unipuncta. Haworth (Noctuidae) and the cabbage looper Trichoplusia ni. Hübner (Noctuidae). Nine major terpenoid constituents of rosemary oil were quantified in the samples by gas chromatography–mass spectrometry (GC-MS). The major constituents were 1,8-cineole, α-pinene, β-pinene, and camphor; on average 1,8-cineole made up 52% of the oil by weight. Bioassayed individually, camphor was the most toxic compound to the armyworm (LD50 = 189.4 μ g larva− 1) whereas μ-terpineol was the most toxic to the looper (LD50 = 128.5 μ g larva− 1). LD50 values for the ten rosemary oils ranged from 167.1 to 372.1 μ g larva− 1in the armyworm and from 58.9 to 335.9 μ g larva− 1 in the looper. Correlation analysis comparing rosemary oil toxicity to chemical composition revealed slight but significant correlation for d.-limonene and α-terpineol in bioassays with the looper but no correlations between constituents and toxicity with the armyworm. An “artificial” rosemary oil was prepared by mixing the nine major constituents in proportions reflecting the average proportion of each constituent in the 10 commercial oils. In the armyworm, this “artificial” oil was significantly less toxic than five of the intact oils; in the looper, the artificial oil was less toxic than three of the intact oils. Our results suggest that toxicity of rosemary oil, at least to lepidopteran larvae, is a consequence of the combined (and possibly synergistic) effects of several chemical constituents, with no individual compound making a dominating contribution.

Arsenic accumulation, biotransformation and localisation in bertha armyworm moths

Environmental context. Insects play an important role in the impact of environmental pollutants such as arsenic. They may accumulate arsenic to high levels, potentially modifying its chemical form, which affects the insects’ toxicity to predators such as fish and birds. Here we use synchrotron X-ray techniques to determine the distribution and chemical form of arsenic in larva, pupa and adult of the bertha armyworm moth. Abstract. Insects are important in bioaccumulation and dispersal of environmental contaminants such as arsenic, and biotransformation of arsenic to various chemical forms directly impacts its toxicity to insects and to their predators. In a model study, the toxic effects and biotransformation of arsenic were examined in larvae, pupae and adults of bertha armyworm moth (Mamestra configurata Walker) (Lepidoptera: Noctuidae). A synthetic diet containing 100 μM arsenate caused reduced larval survival and increased pupal stage duration but no effect on pupal weight or larval stage duration. Synchrotron X-ray absorption spectroscopy (XAS) showed that larvae biotransformed dietary arsenate to yield predominantly trivalent arsenic coordinated with three aliphatic sulfurs, modelled as AsIII-tris-glutathione. Similar species were found in pupae and adults. XAS imaging with micro X-ray fluorescence imaging revealed highly localised arsenic species, and zinc and copper within the gut. The implication of these arsenic species in the diets of predators is discussed.

Effectiveness of three Bt corn events against feeding damage by the true armyworm (Pseudaletia unipuncta Haworth)

A 3-yr study (2002-2004) was conducted to evaluate the resistance of three Bt corn events to herbivory damage by the armyworm, Pseudaletia unipuncta (Haworth). Resistance was assessed by damage ratings and fresh mass measurements. Greenhouse studies were run in 2002 and 2004, and a field study was conducted in 2003. Hybrids expressing the Cry1A(b) insecticidal protein, Mon810 and Bt176 events, and their near isolines, as well as the TC1507 event, which expresses the Cry1F protein, were evaluated. Bt hybrids suffered less damage in all 3 yr and had higher fresh masses in 2002 and 2003 than the non-transgenic isolines. In 2002 and 2003, hybrids expressing the Cry1A(b) protein were significantly less damaged than the hybrid expressing Cry1F. In both 2002 and 2004, the Mon810 event suffered less damage than the Bt176 event, despite expressing the same Cry1A(b) protein. Bt corn, especially the Mon810 event may be used as an effective method of preventing P. unipuncta herbivory damage in corn. Key words: True armyworm, Pseudaletia unipuncta, Bt corn, Cry1A(b), Cry1F, epistasis

Purification, properties and heteromeric association of type-1 and type-2 lepidopteran farnesyl diphosphate synthases

Two forms of farnesyl diphosphate synthase (FPPS) from the spruce budworm, Choristoneura fumiferana, and one from the armyworm Pseudaletia unipuncta, have been cloned and their catalytic properties assessed. The type-2 FPPS of C. fumiferana ( CfFPPS2) was efficient in the prenyl coupling of DMAPP or GPP with [ 14C]IPP, producing FPP as its final product; however, type-1 FPPSs ( CfFPPS1, PuFPPS1, as well as Agrotis ipsilon FPPS1) were essentially inactive. A variety of purification methods was employed to purify the type-1 enzymes. Under mild chromatographic conditions, the isolated type-1 enzyme showed modest activity, but was apparently contaminated with endogenous prenyltransferase derived from the Escherichia coli host cells. Similarly, unpurified extracts of PuFPPS1 expressed in an E. coli FPPS-null mutant, had low FPPS activity. When equimolar amounts of homogenous CfFPPS1 and CfFPP2 were combined, a sharp synergistic enhancement of activity was observed, and the coupling of several homologous substrates, which are precursors to ethyl-branched JHs, was enhanced. Association between CfFPPS1 and CfFPPS2 was confirmed by both protein interaction chromatography and competitive ELISA. These data suggest that type-1 and type-2 FPPSs can form a heteromer, which may play a role in sesquiterpene biosynthesis, such as JH homologue formation, in moths.

Comparative bioactivity of selected extracts from Meliaceae and some commercial botanical insecticides against two noctuid caterpillars, Trichoplusia ni and Pseudaletia unipuncta

Plant-derived extracts and phytochemicals have long been a subject of research in an effort to develop alternatives to conventional insecticides but with reduced health and environmental impacts. In this review we compare the bioactivities of some plant extracts with those of commercially available botanical insecticides against two important agricultural pests, the cabbage looper, Trichoplusia ni and the armyworm, Pseudaletia unipuncta. Test materials included extracts of Azadirachta indica (neem), A. excelsa (sentang), Melia volkensii, M. azedarach (Chinaberry) and Trichilia americana, (all belonging to the family Meliaceae) along with commercial botanical insecticides ryania, pyrethrum, rotenone and essential oils of rosemary and clove leaf. Most of the extracts and botanicals tested proved to be strong growth inhibitors, contact toxins and significant feeding deterrents to both lepidopteran species. However, there were interspecific differences with T. ni generally more susceptible to the botanicals than the armyworm, P. unipuncta. All botanicals were more inhibitory to growth and toxic (through feeding) to T. ni than to P. unipuncta, except for M. azedarach which was more toxic to P. unipuncta than to T. ni. Athough, pyrethrum was the most toxic botanical to both noctuids, A. indica, A. excelsa, and M. volkensii were more toxic than ryania, rotenone, clove oil and rosemary oil for T. ni. As feeding deterrents, pyrethrum was the most potent against T. ni, whereas A. indica was the most potent against the armyworm. Based upon growth inhibition, chronic toxicity, and antifeedant activity, some of these plant extracts have levels of activity that compare favorably to botanical products currently in commercial use and have potential for development as commercial insecticides.

Armyworm, Pseudaletia unipuncta (Haworth) (Insecta: Lepidoptera: Noctuidae)

EENY-394, a 5-page illustrated fact sheet by John L. Capinera, describes this "true armyworm", a light reddish brown nocturnal moth bundant in North America east of the Rocky Mountains, whose larvae are notorious for appearing out of nowhere to inflict a high level of defoliation in grain crops. Includes selected references. Published by the UF Department of Entomology and Nematology, October 2006. EENY-394/IN702: Armyworm, Mythimna unipuncta (Haworth) (Insecta: Lepidoptera: Noctuidae) (ufl.edu)

P2083 Emergence of linezolid resistance of S. epidermidis in a critical care unit

The inhibitory activities of Anethum graveolens, Cuminum cyminum, Foeniculum vulgare and Petroselinum crispum Essential Oils (EOs), plus eleven volatile compounds, on embryonic development of a phytophagous pest, Pseudaletia unipuncta (Lepidoptera: Noctuidae) were evaluated. Lethal and sub-lethal effects of some treatments during the postembryonic development were also monitored. The higher effectiveness to inhibit eggs hatching was achieved with P. crispum fruit EO and its two main compounds (apiole and myristicin). F. vulgare EOs, as well as the bioactive compound azadirachtin (1 mg mL−1) and the volatiles trans-anethole, estragole, (+)-fenchone, α-pinenes, (−)-β-pinene and γ-terpinene (15 mg mL−1), had negligible inhibitory effects on larvae emergence, although, some induced post-exposure mortality during larval phase. A. graveolens EO from leaves and stems, and six compounds, including azadirachtin, extended significantly the duration of larval development from 1.9 to 6.5 days. (+)-Fenchone and (−)-β-pinene reduced significantly the oviposition potential of females, by 46% and 33%, respectively.Additionally, a quantitative nutritional approach was conducted in order to assess adverse effects of EOs and compounds on 4th instar larvae growth and metabolism. After 72 h of feeding with treated corn leaves (0.7 mg/leaf), P. crispum fruit EO (Pc-F) and azadirachtin (0.04 mg/leaf) caused significant adverse effects on larva nutrition (lower consumption and Relative Consumption Rate) and growth (weight loss and negative Relative Growth Rate), followed by trans-anethole and cuminaldehyde. As verified for the positive control azadirachtin, trans-anethole and cuminaldehyde had negative and significant influences on the Relative Metabolic Rate (RMR) and on the efficiency of conversion of food to biomass (measured as ECI and ECD), with consequent higher Metabolic Costs (MC) to the larvae.P. crispum EO from fruits revealed great potential as a controlling agent of P. unipuncta in early life stages, acting as a hatching inhibitor, larvicide and phagodeterrent.

Biochemical, Molecular, and Functional Characterization of PISCF-Allatostatin, a Regulator of Juvenile Hormone Biosynthesis in the Mosquito Aedes aegypti

Aedes aegypti PISCF-allatostatin or allatostatin-C (Ae-AS-C) was isolated using a combination of high performance liquid chromatography and enzyme-linked immunosorbent assay (ELISA). The matrix-assisted laser desorption/ionization time-of-flight (TOF) mass spectrum of positive ELISA fractions revealed a molecular mass of 1919.0 Da, in agreement with the sequence qIRYRQCYFNPISCF, with bridged cysteines. This sequence was confirmed by matrix-assisted laser desorption/ionization tandem TOF/TOF mass spectrometry analysis. The corresponding Ae-AS-C cDNA was amplified by PCR, and the sequence of the peptide was confirmed. An in vitro radiochemical assay was used to study the inhibitory effect of synthetic Ae-AS-C on juvenile hormone biosynthesis by the isolated corpora allata (CA) of adult female A. aegypti. The inhibitory action of synthetic Ae-AS-C was dose-dependent; with a maximum at 10(-9) m. Ae-AS-C showed no inhibitory activity in the presence of farnesoic acid, an immediate precursor of juvenile hormone, indicating that the Ae-AS-C target is located before the formation of farnesoic acid in the pathway. The sensitivity of the CA to inhibition by Ae-AS-C in the in vitro assay varied during the adult life; the CA was most sensitive during periods of low synthetic activity. In addition, the levels of Ae-AS-C in the brain were studied using ELISA and reached a maximum at 3 days after eclosion. These studies suggest that Ae-AS-C is an important regulator of CA activity in A. aegypti.

Characterization and tissue‐specific expression of two lepidopteran farnesyl diphosphate synthase homologs: Implications for the biosynthesis of ethyl‐substituted juvenile hormones

The sesquiterpenoid juvenile hormone (JH) regulates insect development and reproduction. Most insects produce only one chemical form of JH, but the Lepidoptera produce four derivatives featuring ethyl branches. The biogenesis of these JHs requires the synthesis of ethyl-substituted farnesyl diphosphate (FPP) by FPP synthase (FPPS). To determine if there exist more than one lepidopteran FPPS, and whether one FPPS homolog is better adapted for binding the bulkier ethyl-branched substrates/products, we cloned three lepidopteran FPPS cDNAs, two from Choristoneura fumiferana and one from Pseudaletia unipuncta. Amino acid sequence comparisons among these and other eukaryotic FPPSs led to the recognition of two lepidopteran FPPS types. Type-I FPPSs display unique active site substitutions, including several in and near the first aspartate-rich motif, whereas type-II proteins have a more "conventional" catalytic cavity. In a yeast assay, a Drosophila FPPS clone provided full complementation of an FPPS mutation, but lepidopteran FPPS clones of either type yielded only partial complementation, suggesting unusual catalytic features and/or requirements of these enzymes. Although a structural analysis of lepidopteran FPPS active sites suggested that type-I enzymes are better suited than type-II for generating ethyl-substituted products, a quantitative real-time PCR assessment of their relative abundance in insect tissues indicated that type-I expression is ubiquitous whereas that of type-II is essentially confined to the JH-producing glands, where its transcripts are approximately 20 times more abundant than those of type-I. These results suggest that type-II FPPS plays a leading role in lepidopteran JH biosynthesis in spite of its apparently more conventional catalytic cavity.

Insecticidal Activity of the Essential Oil of Ligusticum mutellina Roots

The essential oil obtained from roots of different collections of Ligusticum mutellina was tested against 3rd instar armyworms, Pseudaletia unipuncta (Lepidoptera: Noctuidae), for insecticidal activity. The main compounds were isolated and their structures were elucidated using 2D-NMR techniques. Our collections contained dillapiole, ligustilide and myristicin as major compounds. The previously reported sarisan was not present, moreover its occurrence in L. mutellina should be revised based on our findings.

Visual Recognition of the Host in the Parasitoid Fly Exorista japonica

We presented the tachinid fly Exorista japonica with moving host models: a freeze-dried larva of the common armyworm Mythimna separata, a black rubber tube, and a black rubber sheet, to examine the effects of size, curvature, and velocity on visual recognition of the host. The host models were moved around the fly on a metal arm driven by motor. The size of the larva, the velocity of movement, and the length and diameter of the rubber tube were varied. During the presentation of the host model, fixation, approach, and examination behaviours of the flies were recorded. The fly fixated on, approached, and examined the black rubber tube as well as the freeze-dried larva. Furthermore, the fly detected the black rubber tube at a greater distance than the larva. The rubber tube elicited higher rates of approach and examination responses than the rubber sheet, suggesting that curvature affects the responses of the flies. The length, diameter, and velocity of host models had little effect on response rates of the flies. During host pursuit, the fly appeared to walk towards the ends of the tube. These results suggest that the flies respond to the leading or trailing edges of a moving object and ignore the length and diameter of the object.

Manduca sexta allatotropin and the in vitro biosynthesis of juvenile hormone by moth corpora allata: a comparison of Pseudaletia unipuncta females from two natural populations and two selected lines

We compared the effects of Manduca sexta allatotropin (Manse-AT) on the rate of in vitro juvenile hormone (JH) biosynthesis by the corpora allata (CA) of different-aged virgin females from migrant (Quebec) and non-migrant (Azores) populations of the armyworm, Pseudaletia unipuncta, as well as from early- and late-calling lines selected from the Quebec population. There was a significant age x strain interaction, with the observed rates of JH biosynthesis in early adult life closely reflecting strain-specific differences in the age at onset of calling. In considering data for all ages combined, treatment of CA with Manse-AT resulted in a significant increase in the rate of JH biosynthesis for all but the Late strain, although significant differences for this strain were detected at certain ages. The CA of females from the Azores strain showed the strongest stimulation, with those of 0- and 1-day-old individuals displaying a singularly high degree of sensitivity. Selection for early- and late-calling lines resulted in significant differences in the temporal patterns of JH biosynthesis but did not markedly affect the sensitivity of the CA to Manse-AT. These findings are discussed within the context of the age-related differences observed in the rates of in vitro JH biosynthesis and JH haemolymph titers previously reported in comparisons of the Quebec and Azorean strains of the true armyworm.

Corn Plants Treated with Jasmonic Acid Attract More Specialist Parasitoids, Thereby Increasing Parasitization of the Common Armyworm

We investigated whether corn plants treated with jasmonic acid (JA) increases the ability of the parasitic wasp, Cotesia kariyai, to find and control the common armyworm (Mythimna separata) under laboratory conditions. The rank order of attractiveness increased from intact plants treated with distilled water (DW) (2 d), JA-treated intact plants (2 d), DW-treated infested plants (2 d) to JA-treated infested plants (2 d). Single JA-treatment to either infested or uninfested plants increased attractiveness to C. kariyai over a period lasting at least 10 d. We then showed that the increase in attractiveness of infested corn plants by JA-treatment resulted in increased parasitism by C. kariyai. These results hold a promise for field application of JA-treatment. First, JA-treatment not only promotes the attractiveness of uninfested plants, but also armyworm-infested plants. Thus, parasitoids are not likely to waste time on JA-treated uninfested plants when JA-treated infested plants are available. Second, the effect of JA-treatment is lasting for at least 10 d, a result now obtained in two independent studies.

Host density influences parasitism of the armyworm Pseudaletia unipuncta in agricultural landscapes

Summary Several studies have shown positive responses of parasitism to either host density or landscape complexity. However, no experiments have manipulated host density in landscapes of differing complexity. Here we report the results of a field experiment conducted to determine how host density and agricultural landscape structure jointly affect parasitism and parasitoid diversity of Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae). Parasitism was assessed by experimentally adding P. unipuncta sentinel larvae at low (1 larvae/plant) and high (3 larvae/plant) densities to detect parasitism in commercial cornfields located in a complex and a simple agricultural landscape. The braconid wasps Glyptapanteles militaris (Walsh) and Meteorus spp. accounted for 98.4% of the observed parasitism. Landscape structure did not influence parasitism (80.2% on average) and contrary to expectations, showed a trend towards increased parasitoid richness and diversity in the simple landscape. Increasing host density revealed a trend of increasing parasitoid richness and diversity, and differentially affected parasitism at the parasitoid specific level. G. militaris parasitized a significantly greater proportion of hosts at low host density, while the opposite occurred for Meteorus spp. (primarily M. communis ). These offsetting responses of parasitoids resulted in the lack of an overall host density effect on parasitism. The differential response of these parasitoids to host density is discussed in relation to differences in morphological and life history characteristics. Our results suggest that the specific composition of parasitoid assemblages could significantly alter parasitism at different host densities independently of landscape structural complexity.