European Corn Borer Larvae Research Articles

Volatile-mediated oviposition preference for healthy over root-infested plants by the European corn borer.

The selection of oviposition sites by female moths is crucial in shaping their progeny performance and survival, and consequently in determining insect fitness. Selecting suitable plants that promote the performance of the progeny is referred to as the Preference-Performance hypothesis (or 'mother-knows-best'). While root infestation generally reduces the performance of leaf herbivores, little is known about its impact on female oviposition. We investigated whether maize root infestation by the Western corn rootworm (WCR) affects the oviposition preference and larval performance of the European corn borer (ECB). ECB females used leaf volatiles to select healthy plants over WCR-infested plants. Undecane, a compound absent from the volatile bouquet of healthy plants, was the sole compound to be upregulated upon root infestation and acted as a repellent for first oviposition. ECB larvae yet performed better on plants infested below-ground than on healthy plants, suggesting an example of 'bad motherhood'. The increased ECB performance on WCR-infested plants was mirrored by an increased leaf consumption, and no changes in the plant primary or secondary metabolism were detected. Understanding plant-mediated interactions between above- and below-ground herbivores may help to predict oviposition decisions, and ultimately, to manage pest outbreaks in the field.

Management of inorganic elements by overwintering physiology of cold hardy larvae of European corn borer (Ostrinia nubilalis, Hbn.).

The European corn borer (Ostrinia nubilalis, Hbn.), enters diapause, a strategy characterized by arrest of development and reproduction, reduction of metabolic rate and the emergence of increased resistance to challenging seasonal conditions as low sub-zero winter temperatures. The aim of this study was to investigate the potential role of inorganic elements in the ecophysiology of O. nubilalis, analysing their content in the whole body, hemolymph and fat body, both metabolically active, non-diapausing and overwintering diapausing larvae by ICP-OES spectrometer following the US EPA method 200.7:2001. O nubilalis as many phytophagous lepidopteran species maintain a very low extracellular sodium concentration and has potassium as dominant cation in hemolymph of their larvae. Changes in hemolymph and the whole body sodium content occur already at the onset of diapause (when the mean environmental temperatures are still high above 0ºC) and remain stable during the time course of diapause when larvae of this species cope with sub-zero temperatures, it seems that sodium content regulation is rather a part of diapausing program than the direct effect of exposure to low temperatures. Compared to non-diapausing O. nubilalis larvae, potassium levels are much higher in the whole body and fat body of diapausing larvae and substantially increase approaching the end of diapause. The concentration of Ca, Mg, P and S differed in the whole body, hemolymph and fat body between non-diapausing and diapausing larvae without a unique trend during diapause, except an increase in their contents at the end of diapause.

High-Throughput Feeding Bioassay for Lepidoptera Larvae

Finding plant cultivars that are resistant or tolerant against lepidopteran pests, takes time, effort and is costly. We present here a high throughput leaf-disk consumption assay system, to screen plants for resistance or chemicals for their deterrence. A webcam capturing images at regular intervals can follow the feeding activities of 150 larvae placed into individual cages. We developed a computer program running under an open source image analysis program to analyze and measure the surface of each leaf disk over time. We further developed new statistical procedures to analyze the time course of the feeding activities of the larvae and to compare them between treatments. As a test case, we compared how European corn borer larvae respond to a commercial antifeedant containing azadirachtin, and to quinine, which is a bitter alkaloid for many organisms. As expected, increasing doses of azadirachtin reduced and delayed feeding. However, quinine was poorly effective at the range of concentrations tested (10–5 M to 10–2 M). The model cage, the camera holder, the plugins, and the R scripts are freely available, and can be modified according to the users’ needs.

European corn borer and its parasites overwintering abundance and damages on different corn FAO maturity groups

European corn borer (ECB) is one of the most significant maize pests in the world and also in Croatia. ECB causes yield reduction from 2 to 25%, even more in years favorable for its development. According to estimations, these losses are around 7%. About 90% of the hybrids had some resistance to whorl-leaf feeding (first-generation ECB) and 75% had some resistance to sheath and sheath-collar feeding (second-generation ECB). Along with resistance, modern maize hybrids possess certain level of tolerance. The main aim of this paper was to determine moth eclosion of the overwintering generation and presence of the parasites of ECB larvae during the overwintering as well as to estimate population density of ECB on maize growing area in Croatia. Also, we aimed to establish the differences among different maize FAO maturity groups in damage caused by ECB larvae. Estimated overwintering population was over 8,000 moths/ha i.e. more than 4 million larvae of first generation. During the overwintering four different parasites attacked the larvae. Two species belong to the order Hymenoptera (Cotesia marginiventris Cresson and Eriborus terebrans Gravenhorst) and two species belong to the order Diptera (Ramonda spathulata Fallen and Lydella thompsoni Herting). One caterpillar predator species Paragymnomerus spiricornis Spinola (Hymenopetra) overwinters in maize stalks as well. The highest attack of the first ECB generation was recorded on FAO maturity group 500. The damage from second ECB generation was the highest on FAO groups 400 and 500. The maize of the higher FAO groups has high and robust stems with large number of big leaves. That intensive vegetative growth is a biological characteristic that attracts first generation of ECB to intensifying egg lying. High population level of the first generation also leads to high level of second ECB generation which ultimately caused yield reduced on the hybrids of longer vegetation period (medium-late FAO maturity groups).

Repellent activity of plants from the genus Chenopodium to Ostrinia nubilalis larvae

The olfactory choices expressed by naïve neonate European corn borer (ECB) larvae were tested by recording their locomotor activities in response to odours coming from plants of the genus Chenopodium (producing phytoecdysteroids or not). ECB larvae were found to be repelled from phytoecdysteroid-positive species, except C. album and C. polyspermum. On the contrary, they were mildly attracted or mildly repelled by phytoecdysteroid-negative species, except C. botrys (which emits a rancid odour). These observations indicate that neonate ECB larvae clearly differentiate plant odours and suggest that well-defended plants may emit repellent odours.

The effect of knockdown of insulin receptor substrates 1 and 2 on glucose and lipid metabolism in human hepatoblastoma cells

The European corn borer (Ostrinia nubilalis) is one of the most important insect pests of maize, and has a significant impact on the production of this crop. In this work, we examined the effects of different insecticides on the antioxidative defense system of O. nubilalis larvae. The experimental setup consisted of a completely randomized block design with 4 replicates. Four experimental groups were formed as follows: control (C), indoxacarb (250 mL ha-1), chlorantraniliprole (100 mL ha-1) and the chlorantraniliprole+lambda cyhalothrin (200 mL ha-1) group. Larvae from maize stems were collected 20 days after insecticide application and the whole larvae were homogenized. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST), and the total amount of free SH groups were assessed. Comparison of the experimental groups showed that indoxacarb significantly affected the activities of GST, GPx and the total amount of free SH groups, while chlorantraniliprole significantly affected the activities of SOD, CAT, GST and the total amount of free SH groups, while chlorantraniliprole+lambda cyhalothrin significantly affected the activities of CAT, GST and the total amount of free SH groups. The results show that exposure to insecticides considerably affects the antioxidative defense components of the European corn borer larvae, especially chlorantraniliprole (T2).

Effects of different insecticides on the antioxidative defense system of the European Corn Borer (Ostrinia nubilalis Hübner) (Lepidoptera: Crambidae) larvae

The European corn borer (Ostrinia nubilalis) is one of the most important insect pests of maize, and has a significant impact on the production of this crop. In this work, we examined the effects of different insecticides on the antioxidative defense system of O. nubilalis larvae. The experimental setup consisted of a completely randomized block design with 4 replicates. Four experimental groups were formed as follows: control (C), indoxacarb (250 mL ha-1), chlorantraniliprole (100 mL ha-1) and the chlorantraniliprole+lambda cyhalothrin (200 mL ha-1) group. Larvae from maize stems were collected 20 days after insecticide application and the whole larvae were homogenized. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST), and the total amount of free SH groups were assessed. Comparison of the experimental groups showed that indoxacarb significantly affected the activities of GST, GPx and the total amount of free SH groups, while chlorantraniliprole significantly affected the activities of SOD, CAT, GST and the total amount of free SH groups, while chlorantraniliprole+lambda cyhalothrin significantly affected the activities of CAT, GST and the total amount of free SH groups. The results show that exposure to insecticides considerably affects the antioxidative defense components of the European corn borer larvae, especially chlorantraniliprole (T2).

Research on the Relationship Between the Degree of European Corn Borer (Ostrinia Nubilalis Hbn.) Attack and Maize Fusariosis (Fusarium spp.) at ARDS Turda

The European corn borer (Ostrinia nubilalis Hübn.), which is found almost universally in Europe and America, is an extremely important pest from economic point of view (Szőke et al., 2005). European corn borer larvae cause physical injuries to stalks and ears, and promote infections with Fusarium, by carrying the fungus spores from the plant surface to the surfaces of damaged kernels or to the interior of stalks, where infection occurs (Czembor, 2015). On account of the fact that between Ostrinia nubilalis Hbn. and Fusarium spp. there is a strong connection, and their presence lead to lower maize production, it’s purposed is reducing the corn borer attack, but also the occurrence of maize fusariosis, by applying treatments to the vegetation. The research was carried out at ARDS Turda, in the period 2014-2015 as a bifactorial experience, in which were performed two treatments on growing period, with insecticides, using the products: Avaunt 250 ml/ha (s.a. indoxacarb), Coragen 250 ml/ha (s.a. chlorantraniliprol), Proteus 400 ml/ha (s.a. tiacloprid + deltametrin), Calypso 150 ml/ha (s.a. tiacloprid) and Confidor 400 ml/ha (s.a. imidacloprid + deltametrin), and the biological material was used Turda 165 hybrid. Amid the climatic conditions in the two experimental years (2014-2015), regarding the frecquency attack of the Ostrinia nubilalis, 2015 proved to be a very favorable year for this pest, and by applying treatments to the vegetation, Ostrinia nubilalis Hbn. and Fusarium spp. attack has been reduced very significant. In order to combat the european corn borer (Ostrinia nubilalis Hbn.) chemically, are recommended products based on: chlorantraniliprol and tiacloprid+deltametrin.

A study on percentages of damage ratios of the European corn borer (ECB), Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae) on sweet corn cultivars

The European corn borer (ECB), Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae) is one of the most important pest of grain corn and sweet corn in Turkey. The objective of this study was to assess percentage damage ratios of the ECB on stalk and corncobs of various sweet corn varieties in Reyhanlı district of Hatay province of Turkey. The studies were carried out in 2015-2016 with four different sweet corn varieties including Caremelo, Vega, Merit and Batem. After two years of the study, the ECB larvae caused significant damages on stalk and corncobs of all sweet corn varieties. The percentage damage of stalk and corncobs varied for each of the sweet corn varieties in both years. In the first year, the highest percentages of stalk damage ratios were recorded on Batem (32.45), followed by Vega (19.85), Merit (17.07) and Caremelo (16.72). In the second year, the highest percentages of stalk damage ratios were observed on Merit (59.34), followed by Caremelo (51.65), Batem (45.09) and Vega (35.49). In the first year, the largest percentages of corncobs damage ratios were recorded on Vega (25.73), followed by Batem (16.74), Caremelo (12.11), and Merit (9.30). In the second year, the highest percentages of corncobs damage ratios were observed on Caremelo (14.31), followed by Merit (13.72), Batem (9.98) and Vega (8.93). In conclusion, the largest percentages of stalk + corncobs damages ratios were observed on Batem (49.19), followed by Vega (45.58), Caremelo (28.83) and Merit (26.37) in 2015, while the highest percentages of stalk + corncobs damages ratios were recorded on Merit (73.06), followed by Caremelo (65.96), Batem (55.07) and Vega (44.42) in 2016.

Volatile organic compounds released by maize following herbivory or insect extract application and communication between plants

AbstractTo protect themselves from herbivory, plants have evolved an arsenal of physical and chemical defences and release a variety of volatile organic compounds (VOCs). By releasing theseVOCs, a signalling plant can both reduce herbivory, sometimes by more than 90%, and also warn neighbouring plants about an attack. The aim of this study was to assess the influence of herbivory and insect extract application onVOCrelease by damaged/treated and nearby undamaged/untreated maize plants. We confirmed that European corn borer (Ostrinia nubilalis) larvae attack or larvae extract application induced maizeVOCrelease. Greater amounts of (Z)‐3‐hexenal, (E)‐2‐hexenal, (Z)‐3‐hexen‐1‐ol, (E)‐2‐hexen‐1‐ol,β‐myrcene, (Z)‐3‐hexen‐1‐yl acetate, 1‐hexyl acetate, (Z)‐ocimene, linalool, benzyl acetate, methyl salicylate, indole, methyl anthranilate, geranyl acetate,β‐caryophyllene, (E)‐β‐farnesene and (Z)‐3‐hexenal, (Z)‐3‐hexen‐1‐ol, (Z)‐3‐hexen‐1‐yl acetate, (Z)‐ocimene, linalool, indole, methyl anthranilate, geranyl acetate,β‐caryophyllene and (E)‐β‐farnesene were released as a result of biotic stress after insect attack or insect extract application. The amounts of eachVOCreleased were qualitatively and quantitatively distinct and dependent on time after biotic stress exposure. However, for all biotic stresses, significantly lowerVOCinduction was measured when leaves were damaged/treated for three days, as compared to seven days. Our work also demonstrated that undamaged/untreated neighbouring plants also release significant amounts ofVOCs. This suggests thatVOCemission by a damaged/treated plant stimulatesVOCinduction in nearby undamaged/untreated plants. However, the concentrations of allVOCs released by neighbouring undamaged/untreated maize plants were lower than those from damaged/treated plants and were negatively correlated with distance from a damaged/treated plant. Still, significantVOCinduction occurred in undamaged/untreated plants even at 3 m distance from a damaged/infected plant. Our work suggests that maize plant protective defence responses (VOCemission) can be induced via application of European corn borer extracts.

UTJECAJ ABIOTSKIH ČIMBENIKA NA POJAVU KUKURUZNOG MOLJCA (Ostrinia nubilalis Hubner)

Field experiments with natural population of ECB were conducted in three vegetation seasons (2012-2014) at the Agricultural Institute in Osijek. The aim of this study was to determine the effect of different levels of irrigation and nitrogen fertilization and various genotypes on the occurrence and damage of maize plants from European corn borer larvae and relationship with nitrogen and silicon content as well as C/N ratio. At the end of each growing season were determined ear weight (g), tunnel length (stalk) (cm), ear shank damage (cm), the number of larvae in corn stalk, number of larvae in the ear shank, and total number of larvae in plant. In 2014, with lower temperatures and higher amount of precipitate compared to the previous years, a significantly lower ECB attack was determined. Dominance of Z-type European corn borer on pheromone traps in the area of eastern Slavonia was determined. Increasing the level of soil water content damage from larvae was reduced and increasing the level of nitrogen fertilization feeding activity was increased. We have confirmed different hybrid resistance in regards to damage from larvae, so C4 genotype was the most resistant while C1 was the most susceptible. Concentration of nitrogen and silicon in a maize leaf were in negative correlation as well as nitrogen concentration and C/N ratio. Hybrid resistance didn't entirely depend on nitrogen and silicon concentrations, even though there was greater damage at most hybrids with higher concentration of nitrogen, while damage was reduced with higher concentration of silicon.

Relationship between European Corn Borer injury, Fusarium proliferatum and F. subglutinans infection and moniliformin contamination in maize

The European Corn Borer (ECB), Ostrinia nubilalis (Hübner), plays an important role in promoting Fusarium infection and fumonisin production in maize kernels. Moniliformin (MON) is a mycotoxin that is usually found in association with fumonisins (FB), and as a consequence ECB is also expected to play a role in MON contamination.The aim of the current study was to investigate the influence of ECB activity on MON contamination and on the fungi responsible for its contamination.A comparison has been made between maize infected naturally by insect larvae and protected maize, from 2008 to 2010 in North–West Italy; the latter was obtained by positioning an entomological net at the end of maize flowering.The Fusarium proliferatum infection of the maize grain was higher in each growing season than that caused by Fusarium subglutinans, although both species were significantly increased due to the ECB damage to the maize ears. The ECB activity significantly increased the MON content 26-fold in 2008 from 43 to 1137μgkg−1, 25-fold in 2009 from <LOQ to 77μgkg−1 and 94-fold in 2010 from 6 to 564μgkg−1. The relationship between the MON content and the Fusarium species producers of MON was closer for F. proliferatum (r=0.96, P<0.001) than for F. subglutinans (r=0.83, P<0.001). An in vitro assay was carried on in order to assess the toxigenic capacity of different F. proliferatum and F. subglutinans strains isolated from a field experiment and artificially inoculated on a maize substrate. On average, the F. proliferatum isolated strains showed a significantly higher (P<0.001) toxigenic capacity than the F. subglutinans strains.In conclusion, the combination of the high toxigenic capacity of F. proliferatum, and its more frequent occurrence and greater intensity in the field make it possible to state that the production of MON in maize temperate areas, such as North Italy, is mainly due to F. proliferatum infections and is closely linked to the injury caused by ECB larvae.

European Corn Borer (Ostrinia nubilalis) Induced Responses Enhance Susceptibility in Maize

Herbivore-induced plant responses have been widely described following attack on leaves; however, less attention has been paid to analogous local processes that occur in stems. Early studies of maize (Zea mays) responses to stem boring by European corn borer (ECB, Ostrinia nubilalis ) larvae revealed the presence of inducible acidic diterpenoid phytoalexins, termed kauralexins, and increases in the benzoxazinoid 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one-glucose (HDMBOA-Glc) after 24 h of herbivory. Despite these rapidly activated defenses, larval growth was not altered in short-term feeding assays. Unexpectedly, ECB growth significantly improved in assays using stem tissue preconditioned by 48 h of larval tunneling. Correspondingly, measures of total soluble protein increased over 2.6-fold in these challenged tissues and were accompanied by elevated levels of sucrose and free linoleic acid. While microarray analyses revealed up-regulation of over 1100 transcripts, fewer individual protein increases were demonstrable. Consistent with induced endoreduplication, both wounding and ECB stem attack resulted in similar significant expansion of the nucleus, nucleolus and levels of extractable DNA from challenged tissues. While many of these responses are triggered by wounding alone, biochemical changes further enhanced in response to ECB may be due to larval secreted effectors. Unlike other Lepidoptera examined, ECB excrete exceedingly high levels of the auxin indole-3-acetic acid (IAA) in their frass which is likely to contact and contaminate the surrounding feeding tunnel. Stem exposure to a metabolically stable auxin, such as 2,4-dichlorophenoxyacetic acid (2,4-D), promoted significant protein accumulation above wounding alone. As a future testable hypothesis, we propose that ECB-associated IAA may function as a candidate herbivore effector promoting the increased nutritional content of maize stems.

Implications of European corn borer, Ostrinia nubilalis, infestation in an Aspergillus flavus‐biocontrolled corn agroecosystem

A novel biocontrol strategy consisting of field application of bioplastic-based granules inoculated with a non-toxigenic Aspergillus flavus L. strain has recently been shown to be effective for reducing aflatoxin contamination in corn. This study focused on other factors that may affect the feasibility of this biocontrol technique, and more specifically the role of the European corn borer (ECB), Ostrinia nubilalis H., in the dispersal and infestation of A. flavus in corn and its impact on crop yield. In spite of the high percentage of corn ears showing larval feeding damage, ECB-bored kernels accounted for only 3 and 4% in 2009 and 2010 respectively. Most of the damaged kernels were localised in the ear tip or immediately below. More precisely, the average incidence of ECB-bored kernels in the upper end of the ear was 32%. However, less than 5% of kernels from the central body of the ear, which includes the majority of kernels, were injured by ECB. Although ECB larvae showed a high tolerance to aflatoxin B1 and thus had the potential to serve as vectors of the mould, fungal infection of kernels was poorly associated with insect damage. ECB infestation resulted in grain yield losses not exceeding 2.5%.

E60

The purpose of this study was to evaluate foliar insecticide treatments against caterpillar pests in conventional and Bt sweet corn at the Central Crops Research Station in Clayton, NC. The trial was arranged in a RCB with 8 treatments and four replicates. Plots were 3 rows by 35 ft long planted on 38 inch centers. Sweet corn seed was planted on 24 May 2011 using a single row push planter with 8 inch within row plant spacing. Foliar sprays were made every two days beginning at first silk and continuing until harvest. Insecticide applications were made on 8, 10, 12, 14, 16, 18, 20, 22, 24 Jul. All treatments were applied with a CO2 powered backpack sprayer with a four nozzle boom equipped with DC23 cores and D1 discs delivering 15 gpa at 40 psi. Sprays were directed at the silks with two drop nozzles on each side of the row. One ear was harvested from each of 10 consecutive plants in the second row of each plot on 25 Jul. Ears were transported to NCSU facilities in Raleigh, NC for damage evaluation. The number of corn earworm (CEW) damaged ears and the number of larvae per ear was recorded. The length of CEW damage was measured for each damaged ear. The number of European corn borer (ECB) larvae in each ear was recorded. Treatment means were analyzed using the General Linear Model Procedure in SAS (Version 9.1). When treatment differences were indicated by GLM, means were separated by LSD. All percent data were subjected to arcsine square root transformation prior to analysis. Untransformed data are presented.

The use of entomopathogenic fungus Isaria fumosorosea to reduce harmfulness of European corn borer (Ostrinia nubilalis Hbn.) in cultivation of sweet maizeWykorzystanie grzyba owadobójczego Isaria fumosorosea do ograniczania szkodliwości omacnicy prosowianki (Ostrinia nubilalis Hbn.) w uprawie kukurydzy cukrowej

Summary The field experiment was carried out in 2009–2011 year, in Niziny village, near the city of Przemysl. The aim of the studies was to evaluate the effectiveness of Isaria fumosorosea for the control of Ostrinia nubilalis. Two protection treatments were used: seed dressing with spores of the entomopathogenic fungus and spraying plants during vegetation with spore suspension. The results showed, that the application of I. fumosorosea may reduce the damage caused by larvae of European corn borer (O. nubilalis) in stem and cob in comparison to unprotected plants.

Modelling species abundance using the Poisson-Tweedie family

The distribution of an organism species in the environment deviates frequently from randomness due to natural cycles, availability of food resources and avoidance of harm. As a result, observed data can show over-dispersion, zero-inflation and even heavy tail. Models such as the negative binomial (NB), Poisson-inverse Gaussian (PIG), and zero-inflated Poisson are frequently used in applications instead of the Poisson distribution which is usually the default model. This paper uses a three-parameter discrete distribution that unifies distributions such as Poisson, NB, PIG, Neyman Type A, and Poisson-Pascal. The three-parameter family covers a wide range of tail heaviness relative to NB, and thus suitable for modelling over-dispersed count data with a shorter or longer tail. Moreover, it shows some capacity for zero-inflated data. Grouped counts of coliform bacteria from Lake Erie and counts of European corn borer larvae in field corn are used to illustrate the application of the model and the associated likelihood-based inferences. Copyright © 2010 John Wiley & Sons, Ltd.

A Technique Using Reusable Components for Hand-Infesting Cornstalks With European Corn Borer (Lepidoptera: Crambidae) Larvae

Field trials were conducted in 2005 and 2006 to evaluate the use of reusable wire nuts and nonreusable gelatin capsules for hand-infesting cornstalks with European corn borer, Ostrinia nubilalis (Hübner), (Lepidoptera: Crambidae) larvae. The reusable technique, which consists of a modified WingGard plastic wire connector (i.e., wire nut) as a containment device for larvae, was compared over three plant growth stages to a gelatin capsule technique. In 2005 and 2006, the wire nut technique resulted in significantly higher number of wire nuts still intact (i.e., undamaged, with or without a larva) on the stalk at 72 h after infestation compared with the gelatin capsule technique. In addition, the wire nut technique resulted in significantly higher number of tunnels per stalk compared with the gelatin capsule technique at all three corn growth stages during both years. In 2005, the mean +/- SEM number of tunnels per stalk was 0.53 +/- 0.03 in the wire nut technique compared with 0.13 +/- 0.03 tunnels per stalk in the gelatin capsule technique. In 2006, the mean number of tunnels per stalk was 0.45 +/- 0.03 in the wire nut technique compared with 0.08 +/- 0.02 tunnels per stalk in the gelatin capsule technique. In addition, the relative net precision in the wire-nut technique was approximately 2 times higher compared with the gelatin capsule technique.

Effects of combining Beauveria bassiana and Nosema pyrausta on the mortality of Ostrinia nubilalis

Abstract We tested the combined effect of the fungus Beauveria bassiana and the microsporidium Nosema pyrausta on the European corn borer larvae, Ostrinia nubilalis, in the laboratory. The first instar of O. nubilalis larvae was the most sensitive to the B. bassiana infection followed by the fifth, second, third, and fourth instar (LC50s were 4.91, 6.67, 7.13, 9.15, and 6.51 × 105 conidia/ml for the first to fifth instars, respectively). Mortality of each instar increases positively with concentration of conidia. When B. bassiana and N. pyrausta were used in combination, mortality increased significantly in all instars. Relative to the B. bassiana treatment alone, the B. bassiana + N. pyrausta treatment decreased the LC50s by 42.16%, 37.63%, 21.60%, 27.11%, and 33.95% for the first to fifth instars, respectively. The combined effects of the two pathogens were mostly additive. However, at the two highest concentrations the pathogens interacted synergistically in the first and second instar. Individuals that survived the B. bassiana and B. bassiana + N. pyrausta treatments and developed into adults had significantly shorter lifespans and females oviposited fewer eggs than non-exposed insects. The effects on the longevity and the egg production were most pronounced at high concentration of B. bassiana conidia.

European Corn Borer (Lepidoptera: Crambidae) Infestation Level and Plant Growth Stage on Whole-Plant Corn Yield Grown for Silage in Virginia

Field experiments were conducted in 2004 and 2005 to determine the effect of different levels of hand-infested third instar European corn borer, Ostrinia nubilalis (Hiibner) (Lepidoptera: Crambidae), on whole-plant yield and plant growth stage in corn, Zea mays L., grown for silage. In 2004 and 2005, European corn borer infestation level had a significant negative impact on whole-plant yield (grams of dry matter per plant) with increasing infestation; however, whole-plant yield was not significantly affected by plant growth stage in either year. In 2004, the six larvae per plant treatment caused the greatest percentage of reduction (23.4%) in mean (+/-SEM) whole-plant yield (258.5 +/- 21.0 g dry matter per plant) compared with the Bacillus thuringiensis (Bt) CrylAb control (337.3 +/- 11.1 g dry matter per plant). In 2005, the five larvae per plant treatment caused the greatest percentage of reduction (8.3%) in mean whole-plant yield (282.3 +/- 10.8 g dry matter per plant) compared with the Bt CrylAb control (307.8 +/- 8.3 g dry matter per plant). The relationship between mean whole-plant yield and European corn borer larvae infestation level from the pooled data of both years was described well by using an exponential decay model (r2 = 0.84, P = 0.0038). The economic injury level for silage corn was estimated to be approximately 73% higher than for corn grown for grain based on similar control costs and crop values. In addition, plant growth stage and European corn borer infestation level had no effect on percentage of acid detergent fiber, neutral detergent fiber, and crude protein values in either year of the study.