Corn-growing Regions Research Articles

Trends towards Lower Susceptibility of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Teflubenzuron in Brazil: An Evidence for Field-Evolved Resistance

Susceptibility monitoring to insecticides is a key component to implementing insecticide resistance management (IRM) programs. In this research, the susceptibility to teflubenzuron in Spodoptera frugiperda (J.E Smith) was monitored in more than 200 field-collected populations from major corn-growing regions of Brazil, from 2004 to 2020. Initially, we defined a diagnostic concentration of 10 µg mL-1 of teflubenzuron using a diet-overlay bioassay for monitoring the susceptibility. A variation in the susceptibility to teflubenzuron in S. frugiperda was detected among populations from different locations. We also detected a significant reduction in the susceptibility to teflubenzuron throughout time in all the populations of S. frugiperda evaluated, with larval survival at diagnostic concentration varying from values of <5% in 2004 to up 80% in 2020. Thus, this research provides evidence of field-evolved resistance of S. frugiperda to teflubenzuron and reinforces that IRM practices are urgently needed to be implemented in Brazil.

Genetic Differentiation and Mixed Reproductive Strategies in the Northern Corn Leaf Blight Pathogen Setosphaeria turcica From Sweet Corn in Fujian Province, China.

The northern corn leaf blight (NCLB) pathogen Setosphaeria turcica (Luttrell) Leonard and Suggs is one of the main biotic constraints on sweet corn (Zea mays L.) yield and quality in Fujian Province, China. Currently, however, there is comparatively little information available regarding the distribution of mating types, population genetics, and reproductive strategies of this pathogen in Fujian. In this study, we investigated the distribution of mating types and population genetics of 117 isolates of S. turcica collected from seven of the main sweet corn-growing regions in Fujian Province, based on multiple polymerase chain reaction analyses using two mating type-specific primer pairs and 11 inter-simple sequence repeat markers. Furthermore, we examined the mode of reproduction of Fujian S. turcica populations. Both MAT1-1 and MAT1-2 mating types were detected throughout all seven sampling locations. The majority of MAT1-2 isolates were detected from Dongyou, Jian’ou, Pingnan, Songxi, and Longyan, whereas a large proportion of the detected MAT1-1 isolates were among those collected from Dongfeng and Nanjing. Furthermore, we detected five shared multi-locus haplotypes among S. turcica isolates from Dongyou, Jian’ou, Pingnan, Nanjing, and Songxi, whereas no shared haplotypes were observed between the Dongfeng (or Longyan) population and these five populations. Pairwise comparisons of the indices ΦPT and Nm, and population structure and principal coordinate analyses indicated genetic differentiation between both the regional and the mating type populations of S. turcica in Fujian. The skewed mating type ratio associated with low a haplotypic diversity and evident linkage disequilibrium reveals a mixed reproductive strategy for S. turcica populations in Fujian Province. The findings of this study advance our current understanding of the genetic diversity, population structure, and reproductive strategies of S. turcica populations infecting sweet corn in Fujian Province, and will potentially contribute to further resistance breeding efforts.

The Diversity and the Abundance ofCorn Planthopper(Hemiptera: Delphacidae)inLampung Province

The outbreak of delphacid planthoppers has been detected across corn-growing regions in South Lampung. Survey study was conducted in three corn fields in Natar District, South Lampung Regency. In each study site, five corn plants were randomly sampled. In each sampled plant, one leaf with maximum number of planthoppers was selected for population recording. Based on the morphological identification results, there were two types of corn planthoppers attacking corn fields during sampling periods: the white bellied-planthopper, Stenocranus pacivicus Kirkaldy and Peregrinus maidis Ashmead. During sampling periods, S. pacivicus was most abundant species, while, the Peregrinus planthopper was almost undetectable. There was similar trend peak of density S. pacificus brachypters & nymph and macropters among the three corn fields. The maximum number of S. pacificus brachypters & nymph 412.38 ±23.12 individuals’ leaf−1 was recorded at 70 days after planting (DAP). While the S. pacificus macropters reached the highest population number 43.81 ± 5,76 individuals leaf−1. Extended feeding activity by planthoppers caused the chlorosis and necrosis of the leaf, reduced plant vigor, and stunting, resulting hopperburn symptoms. The results of this study confirm that the explosion of delphacid planthopper sand corn hopperburn are real and become a threat for corn production in Lampung Province.

Low risk of resistance evolution of Spodoptera frugiperda to chlorfenapyr in Brazil

Insecticide resistance is serious problem for Spodoptera frugiperda (Lepidoptera: Noctuidae). Due to intense selection pressure, the evolution of S. frugiperda resistance to major insecticides groups and Bt proteins has already been documented. Therefore, studies to preserve the lifetime of insecticides with unique modes of action such as chlorfenapyr are important in insect resistance management programs. For implementing a proactive resistance management program of S. frugiperda to chlorfenapyr, studies were conducted with field populations collected from major corn-growing regions in Brazil from 2016 to 2018. We aimed to (i) characterize and monitor the susceptibility of field populations, (ii) estimate the frequency of resistance alleles and (iii) evaluate cross-resistance patterns between insecticides and Bt-resistant strains of S. frugiperda to chlorfenapyr. Baseline susceptibility of field population showed a LC50 ranged from 18.3 to 25.1 µg ml−1. The survival rate at the diagnostic concentration ranged from 0 to 8.4%. Using the F2 screen method, the overall estimated resistance allele frequency was 0.0003. No cross-resistance was observed between chlorfenapyr and other insecticides and Bt proteins. Results demonstrated a high susceptibility, low frequency of resistance alleles and lack of cross-resistance. Thus, we concluded there is a low risk of resistance evolution of S. frugiperda to chlorfenapyr in Brazil using the current pest management strategies.

Chronic exposure to neonicotinoids reduces honey bee health near corn crops.

Experiments linking neonicotinoids and declining bee health have been criticized for not simulating realistic exposure. Here we quantified the duration and magnitude of neonicotinoid exposure in Canada's corn-growing regions and used these data to design realistic experiments to investigate the effect of such insecticides on honey bees. Colonies near corn were naturally exposed to neonicotinoids for up to 4 months-the majority of the honey bee's active season. Realistic experiments showed that neonicotinoids increased worker mortality and were associated with declines in social immunity and increased queenlessness over time. We also discovered that the acute toxicity of neonicotinoids to honey bees doubles in the presence of a commonly encountered fungicide. Our work demonstrates that field-realistic exposure to neonicotinoids can reduce honey bee health in corn-growing regions.

Quantitative trait locus mapping and functional genomics of an organophosphate resistance trait in the western corn rootworm, Diabrotica virgifera virgifera.

The western corn rootworm, Diabrotica virgifera virgifera, is an insect pest of corn and population suppression with chemical insecticides is an important management tool. Traits conferring organophosphate insecticide resistance have increased in frequency amongst D. v. virgifera populations, resulting in the reduced efficacy in many corn-growing regions of the USA. We used comparative functional genomic and quantitative trait locus (QTL) mapping approaches to investigate the genetic basis of D. v. virgifera resistance to the organophosphate methyl-parathion. RNA from adult methyl-parathion resistant and susceptible adults was hybridized to 8331 microarray probes. The results predicted that 11 transcripts were significantly up-regulated in resistant phenotypes, with the most significant (fold increases ≥ 2.43) being an α-esterase-like transcript. Differential expression was validated only for the α-esterase (ST020027A20C03), with 11- to 13-fold greater expression in methyl-parathion resistant adults (P < 0.05). Progeny with a segregating methyl-parathion resistance trait were obtained from a reciprocal backcross design. QTL analyses of high-throughput single nucleotide polymorphism genotype data predicted involvement of a single genome interval. These data suggest that a specific carboyxesterase may function in field-evolved corn rootworm resistance to organophosphates, even though direct linkage between the QTL and this locus could not be established.

Evaluating the potential role of denitrifying bioreactors in reducing watershed-scale nitrate loads: A case study comparing three Midwestern (USA) watersheds

The transport of nitrate (NO3-N) from agricultural lands to surface waters is a complex and recalcitrant problem. Subsurface drainage systems that are especially prevalent in the corn-growing regions of the Midwestern USA facilitate NO3-N transport. Several conservation practices, including fertilizer and manure management, cover crops, natural and installed wetlands, and wood-chip denitrification bioreactors are options that can mitigate NO3-N losses from agricultural lands. Using simple methods of estimation we examine the cumulative volume of denitrification bioreactors required to treat various amounts of NO3-N in base flow, a proxy for tile drainage, at the watershed scale. The use of load duration curves from three different watersheds shows that NO3-N transport is disproportionately skewed toward larger daily base flows. Approximately 50% of the annual NO3-N is transported in largest 30% of daily base flows. Using previous estimates of NO3-N removal by wood-chip bioreactors, we calculated cumulative bioreactor volumes needed to achieve a range of hydraulic residence times (HRT) given rates of base flow observed in three agricultural watersheds. These analyses suggest that cumulative watershed bioreactor volumes sufficient to achieve an HRT of 0.5 days will reduce at least 20% of the total annual NO3-N loss in one watershed and 30% in the other two watersheds. The area required for wood-chip bioreactors would be at most 0.27% of the watershed area.

Using a computer-controlled simulated digestion system to predict the energetic value of corn for ducks

Two experiments were conducted to develop a computer-controlled digestion system to simulate the digestion process of duck for predicting the concentration of ME and the metabolizability of gross energy (GE) in corn. In a calibration experiment, 30 corn-based calibration samples with a previously published ME concentration in 2008 were used to develop the prediction models for in vivo energetic values. The linear relationships were established between in vivo ME concentration and in vitro digestible energy (IVDE) concentration, and between in vivo metabolizability of GE (ME/GE) and in vitro digestibility of GE (IVDE/GE), respectively. In a validation experiment, 6 sources of corn with previously published ME concentration in 2008 randomly selected from the primary corn-growing regions of China were used to validate the prediction models established in the calibration experiment. The results showed that in calibration samples, the IVDE concentration was positively correlated with the AME (r = 0.9419), AMEn (r = 0.9480), TME (r = 0.9403), and TMEn concentration (r = 0.9473). Similarly, the IVDE/GE was positively correlated with the AME/GE (r = 0.95987), AMEn/GE (r = 0.9641), TME/GE (r = 0.9588), and TMEn/GE (r = 0.9637). The coefficient of determination greater than 0.88 and 0.91, and residual SD less than 45 kcal/kg of DM and 1.01% were observed in the prediction models for ME concentrations and ME/GE, respectively. Twenty-nine out of 30 calibration samples showed differences less than 100 kcal/kg of DM and 2.4% between determined and predicted values for 4 ME (AME, AMEn, TME, and TMEn) and for 4 ME/GE (AME/GE, AMEn/GE, TME/GE, and TMEn/GE), respectively. Using prediction models developed from 30 calibration samples, 6 validation samples further showed differences less than 100 kcal/kg of DM and 2% between determined and predicted values for ME and ME/GE, respectively. Therefore, the computer-controlled simulated digestion system can be used to predict the ME and ME/GE of corn for ducks with acceptable accuracy.

Optimum placement of phosphorus for corn/soybean rotations in a strip-tillage system

S trip tillage, a conservation tillage system using very reduced tillage, is attracting much attention throughout the corn-growing regions of the United States. In the northern parts of the Corn Belt, strip tillage often replaces no-till systems on the more poorly drained soils because it provides a warmer tilled seedbed for early planting and faster early growth while maintaining substantial amounts of erosion-minimizing plant residue between the tilled strips. Another benefit of strip tillage is the need for only one field operation between soybean harvest and spring planting—that is, fall strip tillage accompanied by deep-placement of fertilizer phosphorus (P) and potassium (K) in a band 15 to 18 cm (6 to 7 in) deep in the strip. No preplant tillage is needed. From an environmental perspective, deep-band placement is considered to be ideal in terms of eliminating nutrient stratification and reducing the potential for surface runoff of fertilizer P, which can easily occur when fertilizers are broadcasted on the soil surface of no-till systems. From an agronomic perspective, fertilizer placement 10 to 13 cm (4 to 5 in) directly below where the seed will be planted is thought to be ideal in terms of fertilizer P and K use efficiency, early …

Predicting Metabolizable Energy of Normal Corn from its Chemical Composition in Adult Pekin Ducks

Two experiments were conducted to establish an ME content prediction model for normal corn for ducks based on the grain's chemical composition. In Experiment 1, observed linear relationships between the determined ME content of 30 corn calibration samples and proximate nutrients, acid detergent fiber (ADF), and neutral detergent fiber (NDF) were used to develop an ME prediction model. In Experiment 2, 6 samples of corn selected at random from the primary corn-growing regions of China were used for testing the accuracy of ME prediction models. The results indicated that the AME, AMEn, TME, and TMEn were negatively correlated with crude fiber (r = −0.905), ADF (r = −0.915), and NDF (r = −0.95) contents, and moderately correlated with gross energy (GE; r = −0.55) content in corn calibration samples. In contrast, no significant correlations were found for CP, ether extract, and ash contents. According to the stepwise regression analysis, both NDF and GE were found to be useful for the ME prediction models. Because the maximum absolute difference between the in vivo ME determinations and the predicted ME values was 61 kcal/kg, it was concluded that, for White Pekin ducks, the latter could be used to predict the ME content of corn with acceptable accuracy.

Cry1Ab Protein Does Not Persist in Soil After 3 Years of Sustained Bt Corn Use

The purpose of this study was to assess the persistence and accumulation of the Cry1Ab protein in soil as a result of sustained planting of genetically modified Bacillus thuringiensis (Bt) corn hybrids. Soil samples were collected from agricultural fields in five corn-growing regions of the United States where Bt corn hybrids (MON 810 or Bt11) had been planted for at least 3 consecutive yr. At each site, soil samples were collected during the corn-growing period (postanthesis) and again within 6 wk after harvest. Multiple soil specimens from matched Bt cornfields and nearby, non-Bt control fields were analyzed by diet-incorporation insect bioassay, using growth inhibition (GI) of the European corn borer (Ostrinia nubilalis) as the toxicity endpoint. Positive control soil samples containing Cry1Ab protein at the GI50 level (0.05 μg/g soil) were analyzed in tandem with test and control samples to verify that the bioassay was able to detect low levels of Cry1Ab protein. The limit of detection for Cry1Ab protein in soil was 0.03 μg/g soil. The presence of Cry1Ab protein in soil was assessed by statistical comparison of the insect toxicity (GI) of soils collected from Bt and non-Bt (control) cornfields. Only one soil sample, collected postanthesis in a Bt cornfield that had also been treated with carbofuran insecticide, showed insect toxicity. This toxicity was below the GI50 level, and no toxicity was detected in the soil collected from the same plot shortly after harvest. Therefore, there is no evidence of persistence or accumulation of Cry1Ab protein in soils from fields planted for at least three consecutive growing seasons with Bt corn hybrids.

Predicted impact of transgenic, herbicidetolerant corn on drinking water quality in vulnerable watersheds of the mid-western USA.

In the intensely farmed corn-growing regions of the mid-western USA, surface waters have often been contaminated by herbicides, principally as a result of rainfall runoff occurring shortly after application of these to corn and other crops. In some vulnerable watersheds, water quality criteria for chronic human exposure through drinking water are occasionally exceeded. We selected three settings representative of vulnerable corn-region watersheds, and used the PRZM-EXAMS model with the Index Reservoir scenario to predict corn herbicide concentrations in the reservoirs as a function of herbicide properties and use pattern, site characteristics and weather in the watersheds. We compared herbicide application scenarios, including broadcast surface pre-plant atrazine and alachlor applications with a glyphosate pre-plant application, scenarios in which losses of herbicides were mitigated by incorporation or banding, and scenarios in which only glyphosate or glufosinate post-emergent herbicides were used with corn genetically modified to be resistant to them. In the absence of drift, in almost all years a single runoff event dominates the input into the reservoir. As a result, annual average pesticide concentrations are highly correlated with annual maximum daily values. The modeled concentrations were generally higher than those derived from monitoring data, even for no-drift model scenarios. Because of their lower post-emergent application rates and greater soil sorptivity, glyphosate and glufosinate loads in runoff were generally one-fifth to one-tenth those of atrazine and alachlor. These model results indicate that the replacement of pre-emergent corn herbicides with the post-emergent herbicides allowed by genetic modification of crops would dramatically reduce herbicide concentrations in vulnerable watersheds. Given the significantly lower chronic mammalian toxicity of these compounds, and their vulnerability to breakdown in the drinking water treatment process, risks to human populations through drinking water would also be reduced.

Migration pathways of corn earworm (Lepidoptera: Noctuidae) indicated by tetroon trajectories

The corn earworm moth, Helicoverpa zea (Lepidoptera: Noctuidae), is a nocturnal pest insect that is capable of long-distance flights. Buoyant superpressure balloons (tetroons) with attached transponders were tracked as surrogate markers of moths migrating from three corn-growing regions in Texas. Launches were synchronized with peak emergence of corn earworm moths in June and July 1992. The tetroons were launched at the time (approximately 0.5 h after sunset) of peak take off (ascent of moths into the boundary layer) from the corn-growing areas, and ballasted to drift near the altitude (500–1000 m a.g.l) of the maximum insect flight concentration. Each tetroon was followed by a tracking vehicle or the Argos satellite for maximum distances of 466 km per 9 h night flight, and for one to four successive nights. The endpoints of four of the six tetroons that were tracked for 9 h from Weslaco, Texas were clustered within a 40 km radius circle centered 35 km east of Uvalde, Texas. The prorated (9 h) vector-average of National Weather Service forecast trajectories at the surface and 85.0 kPa geopotential-height estimated mean atmospheric displacements 57% as long as, and 3° clockwise from seven observed 9 h tracks of tetroons. Implications of these findings are discussed relative to the prediction of insect migrations and development of area-wide pest management.

Incidence of Western Corn Rootworm Beetles (Coleoptera: Chrysomelidae) on Corn in Virginia from 1987 to 1992

The discovery of western corn rootworm beetles, Diabrotica virgifera virgifera LeConte, in a southwest Virginia corn field in 1985 prompted annual surveys of corn fields in an average of 28 counties across the state from 1987 to 1992. All counties included in the annual surveys were representative of the major corn-growing regions of Virginia. Survey results indicated that western corn rootworm beetles spread rapidly throughout most of the western and central continuous corn-growing regions of the state. In the eastern and southeastern corn-growing regions of the state, where crop rotation is widely practiced, detections of western corn rootworm beetles were less common and typically involved only one to two counties per year from 1987 to 1992.

Using Electrophysiology to Study Plant Disease Development

Plant pathogens (particularly fungi) are responsible for a sizable yearly decrease in the yield of food crops throughout the world. Diseases caused by such pathogens result in alterations in the growth and development of the host plant, which in some cases may be so severe as to prevent use of the susceptible variety. New pathogens may appear relatively rapidly in response to the introduction of new crop cultivars. Introducing the new crop cultivars uniformly across a large growing area increases both the probability of a new pathogenic race arising and the possibility of large-scale crop losses. The success of plant breeders in creating new high-yielding, high-quality crop lines has often led to such widespread planting of closely related crop varieties. As an example, in the early 70's a fungal pathogen of (Helminthosporium maydis, race T) spread rapidly across the corn-growing regions of the United States (Fig. 1). The new corn blight organism increased in response to the widespread planting of lines containing the Texas cytoplasmic male sterility factor. The lines were very susceptible to corn blight disease. Introducing the cytoplasmic male sterility factor into agronomically acceptable lines had simplified breeding techniques used in seed production. In the short time that the corn blight epidemic occurred, it was directly responsible for more than a one billion dollar loss in

RELATIONSHIPS BETWEEN LENGTH OF THE ACTUAL AND EFFECTIVE GRAIN FILLING PERIODS AND THE GRAIN YIELD OF CORN

Studies were conducted near Guelph, Ontario in 1970 and 1971 to examine the relationship between grain yield of corn and two measures of the length of the grain filling period, AFPD (actual filling period duration — days from mid-silking to black layer maturity) and EFPD (effective filling period duration — final kernel size divided by mean rate of kernel dry weight accumulation during the middle of the grain filling period). The studies involved 30 adapted commercial hybrids in 1970 and 35 in 1971, with 27 common to both years. Measures of AFPD and EFPD were highly correlated across years. Positive relationships were evident in each year, and over the averages of 2 yr, between AFPD and EFPD, and between both parameters and grain yield; averaged over 2 yr for 27 hybrids, the correlation coefficients between AFPD and yield, and EFPD and yield, were 0.56 and 0.53, respectively (both significant at [Formula: see text]). In general, results provided support for earlier suggestions that selection for an extended grain filling period could result in increased grain yield. However, notable exceptions existed among hybrids to the overall relationship between length of filling period and yield. The existence of these exceptions may indicate that the general relationships observed between length of filling period and yield were only indirect rather than direct, and that exceptional hybrids with high grain yield, high rate of grain dry matter accumulation, and short grain filling period may represent a better breeding objective in short-season corn-growing regions.