Impact of trap design, windbreaks, and weather on captures of European corn borer (Lepidoptera: Crambidae) in pheromone-baited traps

Pheromone-baited traps are often used in ecological studies of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae). However, differences in trap captures may be confounded by trap design, trap location relative to a windbreak, and changes in local weather. The objectives of this experiment were, first, to examine differences in 0. nubilalis adult (moth) captures among the Intercept wing trap, the Intercept bucket/funnel UNI trap, and the Hartstack wire-mesh, 75-cm-diameter cone trap (large metal cone trap) as well as among three cone trap designs. Second, we examined the influence of the location of the large metal cone trap relative to a windbreak on the number of moths captured. Third, we examined the relationship between nightly mean air temperature, relative humidity, wind speed, precipitation, and the number of moths captured in large metal cone traps. The number of moths captured was significantly influenced by trap design, with large metal cone traps capturing the most moths. Wing and bucket traps were ineffective. Differences among trap captures were significant among trap locations relative to a windbreak. Under strong (>14 kph) or moderate (7 <14 kph) wind speeds, traps located leeward of the windbreak captured the most moths, but when wind speeds were light (<7 kph), traps not associated with windbreaks captured the most moths. The multiple regression model fitted to the relationship between number of moths captured per Julian date and nightly weather patterns was significant. Nightly mean air temperature was the most influential parameter in the model, and its relationship with moth capture was positive.     

Behaviour of male European corn borer, Ostrinia nubilalis Hübner (Lep.; Crambidae) towards pheromone-baited delta traps, bucket traps and wire mesh cone traps

Abstract:  Pheromone-baited traps are used to monitor the flight of European corn borer (ECB; Ostrinia nubilalis ). Traps of various designs are available: bucket traps, delta sticky traps and wire mesh cone traps. However, these traps are not all equally efficient and little is known about the reasons for this difference in efficiency. We investigated the behaviour of ECB males towards bucket traps and delta traps by means of observation in a wind tunnel. We also carried out observations and capture trials with delta traps and wire mesh cone traps in field conditions. Our laboratory studies showed that ECB males were not optimally attracted and were poorly captured by a pheromone baited bucket trap. Furthermore, they were shown to readily enter delta traps in the wind tunnel but were caught after more than three passages through this trap. Field studies showed that wire mesh cone traps captured approximately six times more ECB males than delta traps. Observation of the behaviour of ECB males showed that this difference was due to more efficient moth capture rather than greater attraction of the moth. In total, 31.5% of the 219 males observed close to wire mesh cone traps were caught, vs. 2.5% of the 520 males observed close to delta traps. This greater efficiency is due to a better capture rate of the attracted males by wire mesh cone traps than by delta traps.     

Monitoring populations of saddled prominent (Lepidoptera: Notodontidae) with pheromone-baited traps

Field trials with three types of pheromone traps were performed in eight northern hardwood stands in northern New York state to develop a population-monitoring tool for the saddled prominent, Heterocampa guttivitta (Walker) (Lepidoptera: Notodontidae). Lure specificity and the relationship between pheromone trap catch and subsequent egg density were examined. A study of moth emergence in relation to temperature was designed to determine whether moth activity throughout the flight season can be predicted using a growing degree-day (DD) model. Pherocon 1C wing traps were significantly more effective than the green Unitrap bucket style. Catch was not affected by position when traps were > or =20 m from an opening (road), and lures were specific to saddled prominent. Lure specificity was examined using green Multipher bucket traps, which effectively attracted and held moths. In the first year of the study, number of viable eggs per 10 leaf clusters was significantly correlated (r2 = 0.59) with average moth catch/trap in pheromone-baited Pherocon traps. When differences in stand density (basal area) and relative abundance of sugar maple (percentage of total stems per hectare), the principle host, were accounted for, the multiple regression model also was significant and r2 = 0. 83. Neither model, however, was significant the second year. Using a base temperature of 5.5 degrees C and on-site temperature data, the peak of moth flight occurred at 316 +/- 8 DD and end of flight occurred at 533 +/- 9 DD.     

European corn borer control with Bacillus thuringiensis standardized as corn borer international units

Bacillus thuringiensis products (Dipel and Thuricide HPC) were standardized against the European corn borer, Ostrinia nubilalis, by using standard bioassay techniques. When they were applied on an international unit basis for control of the corn borer on field corn, the granular formulations gave better control of the corn borer than did the spray formulations.     

Monitoring of the European corn borer (Lepidoptera: Crambidae) in central Maine

Pheromone trap types and within-field trap locations were compared for their effectiveness in monitoring the flight activity of European corn borer, Ostrinia nubilalis (Hübner), and its relationship to egg mass density and crop damage in sweet corn in central Maine from 1995 to 1996. The use of both 3:97 Z:E-11-tetradecenyl acetate and 97:3 Z:E-11 tetradecenyl acetate pheromone blends confirmed that European corn borer in central Maine is attracted to both pheromone lure types. European corn borer moths were captured predominantly with the E-lure type than with the Z-lure type in both years. The Scentry Heliothis trap was more effective than the Multi-Pher trap, but similar to the pheromone-baited water pan trap for monitoring European corn borer flights. With the Scentry Heliothis trap, the grassy border and 1st corn rows were the best locations for moth capture during the early flight period, but during the peak flight period, traps located in the middle of the field caught the most moths. Corn damage was recorded before moth captures in some sites and before egg mass counts in others, indicating poor efficacy of traps for early flights. Significant and positive correlations were found between moth captures in the midfield location and egg mass counts, and corn leaf damage, and between egg mass counts and corn leaf damage. However, low coefficients of variation suggest that pheromone trap captures were not good predictors of European corn borer leaf damage in sweet corn.     

Monitoring the Cry1Ab susceptibility of European corn borer in Germany

The European corn borer, Ostrinia nubilalis (Hübner), is one of the most important insect pests in corn, Zea mays L. Transgenic corn cultivars expressing Bacillus thuringiensis (Bt) toxin provide a promising crop protection strategy against European corn borer; however, management is needed to avoid resistance development of the target pest species. The aim of this work was to establish the baseline susceptibility of different European corn borer populations in Germany to be able to forecast a possible development of resistance at an early stage. To standardize test procedures for future resistance management, the efficiency of Cry1Ab toxins from different suppliers and different production was assessed. Furthermore, two different test methods, surface treatment and the incorporation method, were compared with regard to their practicability and efficiency. Neither method provided significant differences in the baseline susceptibility of populations from different German regions. Overall, the data suggested little differentiation among German populations in terms of their susceptibility to Bt toxin and their genetic background. Future monitoring could therefore use a single European corn borer population as a representative for southwestern Germany. However, toxins from different suppliers and different production batches produced a vast range of LC50 values. Changes because of different toxin batches may be mistaken as a change in baseline susceptibility or even as the start of a resistance development. Thus, it is important throughout insect resistance management that the same toxin batches will be available for baseline susceptibility bioassays and for future tests.     

Population consequences of diapause in a model system: the European corn borer

The diapause biology of the European corn borer (ECB), Ostrinia nubilalis (Hübn.), is described based on natural and controlled environment studies of feral and lab-reared ECB's in North Carolina (NC). The diapause response is described as a function of photophase (h of light/day) as well as a function of larval age (instar) at onset of diapause-inducing conditions. A critical photophase of 14.4 h and a critical mean larval instar of 3.3 is found in the lab studies and supported by three years of insectary studies. Seven years of black light trapping of ECB moths in Goldsboro, NC, revealed the likelihood of up to four moth flights/year.Information about the diapause biology of this insect is used to explain both the number of flights and the relative magnitude of the final moth flights. On average, the majority of ECB lineages pass through three generations/year with early maturing ECB's producing a significant and predictable fourth generation. The timing and magnitude of the fourth flight can be partly explained on the basis of the critical photophase and the timing and age structure of previous ECB generations. In most years, the fourth flight is smaller than the third due to the majority of the fourth generation's predisposition towards diapause. However, in at least one case (1977), the fourth flight was unusually large and could be predicted by slight temporal shifts in the previous three flights resulting in the majority of the fourth generation larvae averting diapause. The value of the ECB-diapause interaction as a model system for the explanation and prediction of dynamic phenological events is discussed.

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Résumé La diapause d'O. nubilalis Hubn. est décrite d'après des études en conditions naturelles et programmées de souches sauvages ou élevées au laboratoire en Caroline du Nord. La diapause est décrite comme une fonction de la photophase (heures de jour/24 heures) et du stade larvaire au début des conditions inductrices de la diapause. Une photophase critique de 14,4 h et un stade critique larvaire de 3,3 ont été établis au laboratoire après 3 ans d'études en insectarium. 7 ans de piégeage à la lumière noire à Goldsboro, ont montré la vraisemblance de l'existence de 4 vols par an. Les données sur la diapause de cet insecte sont utilisées pour expliquer tant le nombre de vols que l'importance relative des derniers vols. En moyenne, la majorité des lignées ont 3 générations par an, O. nubilalis précoces produisant une quatrième génération conséquente et prédictible. La data et l'importance du 4ème vol peuvent être partiellement expliquées d'après la photophase critique, et la data et la structure en âge des générations précédentes. La plupart des années, le 4ème vol est moins important que le 3ème par suite de la prédisposition à la diapause de la majorité de la 4ème génération. Cependant, dans un cas au moins, en 1977, le 4ème était anormalement important et pouvait être prédit par de faibles changements temporels dans les 3 précédents vols, détournant de la diapause la majorité des chenilles de 4ème génération. La discussion porte sur la valeur du modèle fourni par la diapause de O. nubilalis pour expliquer et prédire la dynamique des évéments phénologiques.

     

Establishment of Cry9C susceptibility baselines for European corn borer and southwestern corn borer (Lepidoptera: Crambidae)

In 1997 and 1998, Cry9C susceptibility baselines were established for field-collected populations of European corn borer, Osrinia nubilalis (Hubner), and southwestern corn borer, Diatraea grandiosella Dyar. Bioassay of neonate European corn borer larvae of 16 colonies collected from the midwestern United States indicated LC50 values ranging from 13.2 to 65.1 ng of Cry9C protein per square centimeter. Neonate European corn borer LC50 values ranged from 46.5 to 214 ng/cm2. Neonate larvae of three colonies of southwestern corn borer collected from the southern and southwestern United States exhibited LC50 values from 16.9 to 39.9 ng of Cry9C protein per square centimeter. Southwestern corn borer neonate LC90 confidence limit values ranged from 40.3 to 157 ng of Cry9C protein per centimeter. The most sensitive southwestern corn borer colony was collected from the Mississippi delta exhibiting an LC50 value of 22.6 ng of Cry9C per cm2 and also displayed the widest LC0 confidence limits of 40.3-94.8 ng of Cry9C per cm2. Geographic baseline susceptibility data establishes the natural genetic variation and provides the foundation for future testing of insect populations exposed to increased use of Bacillus thuringiensis-based crops. Insect resistance management and stewardship of Cry9C will rely upon baseline data for the validation of discriminating dose assays for European corn borer and southwestern corn borer.     

Fungi associated with eggs and first-instar larvae of the European corn borer

Fungi isolated from field-collected egg masses of the European corn borer, Ostrinia nubilalis, were identified as Alternaria spp., A. porri, Fusarium spp., Fusarium oxysporum, Beauveria bassiana, Mucor spp., and an unidentified yeast. Most fungi were associated with predator injury to the egg mass. Bioassay of fungi on egg masses, however, showed that Alternaria spp. and A. porri reduced the hatch of both injured and uninjured egg masses, and Mucor sp. reduced the hatch only when the egg mass was injured.     

Ancestral feeding and survival of offspring in European corn borer

Experiments were conducted to evaluate the influence of ancestral adult feeding by European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), on larval survival in the field and neonate movement behavior in laboratory. Larval survival was higher when either the grandparental or parental generation had fed, but the feeding sites of the surviving larvae were not affected by ancestral feeding condition. This is the first evidence that grandparental feeding could influence larval survival in the field. Larval movement was observed in the laboratory. Silking speed of neonates was faster when either grandparents or parents had fed, while walking speed was faster only when parents had fed. No broad-sense genetic correlation was found between silking speed and walking speed. Broad-sense heritability among feeding histories were not significant for silking speed, but was significantly greater than zero for walking speed when grandparents fed and parents did not. These intergenerational effects could induce complex population dynamics in this species.     

Dispersal behavior of neonate European corn borer (Lepidoptera: Crambidae) on Bt corn

European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), has historically been a significant economically important insect pest of corn (Zea mays L.) in the United States and Canada. The development in the 1990s of genetically modified corn expressing genes derived from Bacillus thuringiensis (Bt) that encodes insecticidal crystalline (Cry) proteins has proven to be effective in controlling this insect as well as other corn pests. The purpose of this study was to assess the movement and dispersal behavior of neonate European corn borer on Bt corn. We examined differences in neonate European corn borer dispersal behavior for the first 4 h after eclosion in the field among a stacked pyramid (Cry1F X Cry1Ab X Cry34/35Ab1) Bt corn, a Cry1F Bt corn, and a non-Bt sweet corn; and in the laboratory among a Bt corn hybrid containing Cry1F, a hybrid containing Cry1Ab, a pyramid combining these two hybrids (Cry1F X Cry1Ab), and a non-Bt near isoline corn. In field experiments, we found that dispersal was significantly higher on Bt corn compared with sweet corn. In laboratory experiments, dispersal was significantly higher on Cry1Ab Bt corn and Cry1F X Cry1Ab Bt corn than on non-Bt near isoline corn. Results indicated that neonate dispersal may be significantly greater in Bt cornfields compared with non-Bt cornfields. The findings on dispersal behavior in this study will be useful in evaluating the efficacy of a blended seed refuge system for managing European corn borer resistance in Bt corn.     

Economic analysis of planting dates to manage European corn borer (Lepidoptera: Crambidae) with Bt corn

Planting dates of transgenic Bacillus thuringiensis Berliner (Bt) corn were adjusted to determine the utility in managing European corn borer, Ostrinia nubilalis (Hübner). Transgenic Bt (events 176 and Bt11) corn and non-Bt corn were planted at three different times to use the early- and late- planted corn as a potential trap crop for ovipositing European corn borer moths. Grain moisture and yields were recorded to determine the economic benefits of Bt corn planted on the different dates, based on European corn borer populations and corn damage data collected before harvest. Data were recorded from three locations in southwestern, central, and northeastern Iowa for three summers (1996-1998). Economic benefits are discussed in relation to EILs and yield results. Adjusting the planting dates of Bt and non-Bt corn provided variable economic differences among planting dates in northern Iowa; however, greater economic benefits were realized when Bt corn was planted late during the planting sequence in central and southwestern Iowa. These results suggest that planting corn should be conducted in a timely manner and, if delayed or required to plant late, planting Bt corn would likely provide greater economic benefits. Although yield and economic variability were high, using Bt corn in combination with planting date adjustments may be a viable option for managing European corn borer.     

Integrating insecticides and Trichogramma ostriniae to control European corn borer in sweet corn: Economic analysis

We compared the economics of controlling European corn borer (Ostrinia nubilalis) in sweet corn by using the egg parasitoid, Trichogramma ostriniae, alone and integrated with insecticidal sprays. An initial experiment in 2003 compared T. ostriniae alone against insecticide alone and a second set of experiments conducted over 3 years (2006–2008) compared (1) insecticide alone [Insecticide]; (2) no insecticide, no T. ostriniae [Untreated Check]; (3) T. ostriniae alone [T. ostriniae 1X]; and (4) T. ostriniae + insecticide [Integrated]. In 2007 and 2008, a fifth treatment was added consisting of three approximately weekly releases of T. ostriniae [T. ostriniae 3X]. Parasitism of O. nubilalis eggs was higher in plots receiving T. ostriniae; O. nubilalis eclosion was lower with T. ostriniae; there was no interaction of T. ostriniae and insecticide on parasitism, O. nubilalis eclosion, or total O. nubilalis larvae at harvest time. Partial crop budgets were conducted for each treatment. In three of the 4 years, Untreated Checks had the highest sweet corn ear damage. Ear damage after a single release of T. ostriniae was statistically no different than using insecticides. In two of the three years, the Integrated treatment (T. ostriniae 1X + insecticide) generated the largest increase in profitability. The insecticide only treatment generated the second best increase in profitability. When comparing a single release of T. ostriniae to the insecticide only, the latter provided a better combination of efficacy and profitability. The breakeven costs of the T. ostriniae justified their use relative to the Untreated Check treatment, but not when compared to the Insecticide treatment. The breakeven costs for T. ostriniae in the Integrated treatment exceeded the actual cost in two out of three years, suggesting again that conventional growers could benefit from integrating T. ostriniae with insecticidal treatments. Projected profitability based on ear packout obtained by combining data among years suggests that in general, for low prices and yields, the increase in profit is quite modest. In the lowest price-yield combination, the change in profit is T. ostriniae 3X > Integrated > Insecticide > T. ostriniae 1X ? Untreated Check. At high prices and high yields, the differences between the management options when compared to Untreated Check are considerable. In the highest price-yield combination, the change in profit is T. ostriniae 3X > Integrated ? Insecticide > T. ostriniae 1X ? Untreated Check.     

Understanding successful resistance management: the European corn borer and Bt corn in the United States

The European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) has been a major pest of corn and other crops in North America since its accidental introduction nearly a hundred years ago. Wide adoption of transgenic corn hybrids that express toxins from Bacillus thuringiensis, referred to as Bt corn, has suppressed corn borer populations and reduced the pest status of this insect in parts of the Corn Belt. Continued suppression of this pest, however, will depend on managing potential resistance to Bt corn, currently through the high-dose refuge (HDR) strategy. In this review, we describe what has been learned with regard to O. nubilalis resistance to Bt toxins either through laboratory selection experiments or isolation of resistance from field populations. We also describe the essential components of the HDR strategy as they relate to O. nubilalis biology and ecology. Additionally, recent developments in insect resistance management (IRM) specific to O. nubilalis that may affect the continued sustainability of this technology are considered.     

Late-instar European corn borer (Lepidoptera: Crambidae) tunneling and survival in transgenic corn hybrids

Field studies were conducted in 1996 and 1997 to determine injury by and survival of late-instar European corn borer, Ostrinia nubilalis (Hübner), on genetically altered Bacillus thuringiensis Berliner corn, Zea mays L. Cry1Ab events 176, Bt11, MON810, and MON802; Cry1Ac event DBT418; and Cry9C event CBH351 were evaluated. Plants of each corn hybrid were manually infested with two third-, fourth-, or fifth-instar O. nubilalis. Larvae were held in proximity to the internode of the plant above the ear with a mesh sleeve. Larvae were put on the plants during corn developmental stages V8, V16, R1, R3, R4, R5, and R6. This study shows that not all B. thuringiensis hybrids provide the same protection against O. nubilalis injury. Hybrids with B. thuringiensis events Bt11, MON810, MON802, and CHB351 effectively protected the corn against tunneling by late-instar O. nubilalis. Event 176 was effective in controlling late-instar O. nubilalis during V12 and V16 corn developmental stages; however, significant tunneling occurred by fourth instars during R3 and R5. Event DBT418 was not effective in controlling late-instar O. nubilalis during corn vegetative or reproductive stages of development. Whether the B. thuringiensis hybrids satisfied high- and ultra-high-dose requirements is discussed.     

Comparative susceptibility of European corn borer, southwestern corn borer, and sugarcane borer (Lepidoptera: Crambidae) to Cry1Ab protein in a commercial Bacillus thuringiensis corn hybrid

One field strain each of the European corn borer, Ostrinia nubilalis (Hübner); southwestern corn borer, Diatraea grandiosella Dyar; and sugarcane borer, Diatraea saccharalis (F.); were collected from cornfields in northeastern Louisiana. Susceptibilities of the field strain and a corresponding laboratory strain of the three borer species to Cry1Ab protein in DK69-70 Bacillus thuringiensis (Bt) corn hybrid were determined by exposing neonates to intact leaf tissues from whorl stage plants or by feeding neonates or third instars on a meridic diet treated with different concentrations of Cry1lAb protein extracted from Bt corn leaves. Mortality and growth of larvae were evaluated after 2 and 4 d posttreatment in the bioassays by using intact leaf tissues or after 7 d in the bioassays by using diet incorporating Cry1Ab protein. D. saccharalis was the least susceptible species to Cry1Ab protein among the three species, followed by D. grandiosella, whereas O. nubilalis was most susceptible. The 2-d mortality of D. saccharalis neonates on intact Bt leaf tissues was lower than that of O. nubilalis and D. grandiosella. All neonates of O. nubilalis were killed on the diet treated with Cry1Ab protein at 0.5 and 1 mg/kg. The mortality of D. grandiosella was > 75% at 1 mg/kg, but it was < 6% for D. saccharalis at 1 mg/kg. The LC50 values of D. saccharalis were 3- and 11-fold higher than those of D. grandiosella and O. nubilalis, respectively. The LC90 values of D. saccharalis were 8- and 32-fold higher than those of D. grandiosella and O. nubilalis, respectively. Larval growth of the three species on Cry1Ab-treated diet was inhibited, but the inhibition was greater for O. nubilalis and D. grandiosella than for D. saccharalis. The lower susceptibility of D. saccharalis to Cry1Ab protein suggests that it is necessary to verify if a high-dose Bt corn for O. nubilalis and D. grandiosella is also a high dose for D. saccharalis.     

Development of European corn borer larvae on Event 176 Bt corn: influence on survival and fitness

European corn borer larvae, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) that have completed development on Event 176 Bt corn hybrids have survived exposure to sublethal doses of the Cry1Ab Bt toxin or are exploiting plant tissues that do not express the toxin. To evaluate the impact of such exposure, diapausing larvae were collected from Event 176 and conventional hybrids and compared for rates of pupation, parasitism, fitness (pupal weight, longevity, and fecundity) and susceptibility to the Cry1Ab toxin. Larvae completing development on Event 176 corn exhibited approximately 10% higher survival rates and correspondingly lower parasitism rates than larvae completing development on conventional hybrids. No significant differences were detected in pupal weight, fecundity, longevity or susceptibility to the Cry1Ab Bt toxin. These results indicate that survival on Event 176 corn are not adversely affect fitness and does not cause increased tolerance to the Cry1Ab toxin in subsequent generations.     

Field trapping of the flathead oak borer Coroebus undatus (Coleoptera: Buprestidae) with different traps and volatile lures

The flathead oak borer Coroebus undatus F. (Coleoptera: Buprestidae) is one of the primary pests of cork oak Quercus suber L. in the Mediterranean region causing great economic losses to the cork industry. Very little is known about its biology and behavior and, so far, no control measures have been established. We present the results of a pilot study aimed to develop an efficient trapping method for monitoring this harmful pest. In a 3‐year field study, purple‐colored prism traps baited with a mixture of green leaf volatiles (GLVs) from the host have been shown the most effective combination to catch C. undatus adults (solely females) compared to other trap and lure types tested. Wavelength and reflectance measurements revealed that purple traps exhibit reflectance peak values similar to those found in the abdominal and elytral cuticle of both sexes, suggesting the involvement of visual cues for mate location in this species. The data presented are the first to demonstrate captures of adults of the genus Coroebus by an attractant‐based trapping method.     

Pheromone-blend discrimination by European corn borer moths with inter-race and inter-sex antennal transplants

Transplantation of larval antennal imaginal disks between the pheromone races of the European corn borer moth produced males and females of one race with male antennal phenotypes of the race using the opposite pheromone blend. All of the adults with transplanted antennal disks that exhibited a pheromone-mediated response in the flight tunnel did so with the pheromone blend of the recipient's race, even though the respective males and females possessed male antennae of the opposite race. Our results support the conclusion that male antennal response type is not a determining factor in pheromone-blend discrimination in male moths. Accepted: 13 November 1998