Armyworm Pseudaletia Unipuncta Research Articles

Green Cane Harvest Effect on Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae) Larvae Abundance and Losses Caused by This Pest in Tucumán, Argentina

From 2010 to 2012 harvest seasons, studies of the armyworm Pseudaletia unipuncta were conducted in sugarcane in Tucuman. The larvae are nocturnal and during the day remain hidden under the crop residues or in the soil. Damage begins in spring when temperature rises. They produce damage by feeding and killing the shoots, delaying the growth of the new shoots in the cane field. This study aimed to evaluate the effect of agricultural residues of sugarcane green harvest on larval abundance and the losses caused by this armyworm. Trials were conducted at three locations. Twelve points of 2 m row length were evaluated every 15 days from September to November. The number of larvae and percentage of affected shoots were evaluated. When the attack of P. unipuncta began in September, a plot of 1 ha was sprayed with pesticides, and another plot was left with harvest residues and the pest. Five samples of 10 stalks were extracted per plot. Factory parameters (pol, brix) were evaluated in the lab. Localities averaged shoot losses between 13 and 30 %. The average relative abundance of larvae in the plots with harvest residues was 0.5 larvae per 2 m row; no larvae were found in plots without residues. Factory sugar yield was 10.7 % in the plot without insecticidal control and 12 % in the treated plot, with a total sugar loss of 23.2 % per ha. To prevent losses caused by this species, it is important to sample early green cane harvested fields in spring.

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.

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.

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.

Effect of Food Resources on Adult <I>Glyptapanteles militaris</I> and <I>Meteorus communis</I> (Hymenoptera: Braconidae), Parasitoids of <I>Pseudaletia unipuncta</I> (Lepidoptera: Noctuidae)

Adult parasitoids frequently require access to food and adequate microclimates to maximize host location and parasitization. Realized levels of parasitism in the field can be significantly influenced by the quantity and distribution of extra-host resources. Previous studies have demonstrated a significant effect of landscape structure on parasitism of the armyworm Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae). As a possible mechanism underlying this pattern, we investigated the effect of carbohydrate food sources on the longevity and fecundity of armyworm parasitoids under laboratory conditions of varying temperature, host availability, and mating status. Glyptapanteles militaris (Walsh) (Hymenoptera: Braconidae) adults lived significantly longer when provided with honey as food and when reared at 20°C versus 25°C. Meteorus communis (Cresson) (Hymenoptera: Braconidae) adults also lived significantly longer when provided with honey, although longevity was reduced when females were provided hosts. Honey-fed females of M. communis parasitized significantly more hosts because of their increased longevity, but did not differ in daily oviposition from females provided only water. Mating significantly increased parasitism by honey-fed M. communis, but not those provided water alone. These results indicate that the presence of both carbohydrate resources and moderated microclimates may significantly increase the life span and parasitism of these parasitoids. However, the greater longevity and lower daily rate of oviposition of M. communis suggest that food and microclimate resources are more critical for this species than for the shorter lived, gregarious G. militaris. These findings contribute to our understanding of how these two parasitoids respond to landscape complexity.

Densidad y daños de plagas del maíz, bajo labranza convencional y de conservación

Se estudiaron los efectos de los sistemas de labranza convencional y de conservación sobre la incidencia y el daño del gusano cogollero Spodoptera frugiperda (J.E. Smith), gusano soldado de punto Pseudaletia unipuncta (Haworth) y el picudo chico Nicentrus testaceipes (Champion) en maíz, durante el ciclo agrícola primavera-verano de 1998, en Chapingo, México. Para determinar el número de insectos y lesiones en las plantas de maíz, se realizaron seis muestreos con intervalos de 20 días, revisando en forma visual 50 plantas por unidad experimental. En el caso particular del gusano soldado, se estimó la densidad de larvas en el suelo y la proporción de hojas de maíz con lesiones. Respecto de los picudos, se cuantificaron las lesiones que causaron en tres porciones de la hoja ocho. Los porcentajes máximos de plantas dañadas por el gusano cogollero fueron de 20% en labranza convencional y 4% en conservación. Las larvas del gusano soldado sólo se presentaron en conservación, asociadas a la maleza Brachiaria plantaginea, en la que iniciaron el daño, y de la cual consumieron 94.5% del follaje. Cincuenta y dos punto siete porciento del total de las hojas (inferiores) del maíz presentaron lesiones causadas por el gusano soldado. La proporción de plantas afectadas por el picudo fue de 95% en labranza de conservación, y de 84% en convencional. Así mismo, el número total de lesiones en la octava hoja fue de 44.4 y 10.8, respectivamente.

Axenic culture of the armyworm Pseudaletia unipuncta (Haworth) on a meridic diet.

Axenic culture of the armyworm Pseudaletia unipuncta (Haworth) on a meridic diet.