Greenbug Density Research Articles

Airborne Remote Sensing to Detect Greenbug1Stress to Wheat

Abstract. Vegetation indices calculated from the quantity of electromagnetic radiation reflected from plants measured using multi-spectral imaging systems have been used to quantify stress levels in plants. Greenbugs, Schizaphis graminum (Rondani), cause stress to wheat, Triticum aestivum L., plants and therefore multispectral remote sensing may be useful for detecting greenbug-infested wheat fields. The objectives of this study were to assess whether variation in light reflectance from plants infested with varying densities of greenbugs could be detected and quantified using airborne imagery obtained with a multi-spectral digital camera mounted in a fixed-wing aircraft. In a replicated experiment where greenbug density was manipulated in 1-m2 plots of two winter wheat varieties (‘Jagger’ and ‘OK 101’) planted in a 1 ha field, we found that wheat infested with greenbugs exhibited a similar reflectance response for the two varieties. Both varieties showed a reduction in the normalized differenced vegetatio...

Hyperspectral Spectrometry as a Means to Differentiate Uninfested and Infested Winter Wheat by Greenbug (Hemiptera: Aphididae)

Although spectral remote sensing techniques have been used to study many ecological variables and biotic and abiotic stresses to agricultural crops over decades, the potential use of these techniques for greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae) infestations and damage to wheat, Triticum aestivum L., under field conditions is unknown. Hence, this research was conducted to investigate: 1) the applicability and feasibility of using a portable narrow-banded (hyperspectral) remote sensing instrument to identify and discern differences in spectral reflection patterns (spectral signatures) of winter wheat canopies with and without greenbug damage; and 2) the relationship between miscellaneous spectral vegetation indices and greenbug density in wheat canopies growing in two fields and under greenhouse conditions. Both greenbug and reflectance data were collected from 0.25-, 0.37-, and 1-m2 plots in one of the fields, greenhouse, and the other field, respectively. Regardless of the growth conditions, greenbug-damaged wheat canopies had higher reflectance in the visible range and less in the near infrared regions of the spectrum when compared with undamaged canopies. In addition to percentage of reflectance comparison, a large number of spectral vegetation indices drawn from the literature were calculated and correlated with greenbug density. Linear regression analyses revealed high relationships (R2 ranged from 0.62 to 0.85) between greenbug density and spectral vegetation indices. These results indicate that hyperspectral remotely sensed data with an appropriate pixel size have the potential to portray greenbug density and discriminate its damage to wheat with repeated accuracy and precision.

Spatial and Temporal Distribution of Induced Resistance to Greenbug (Homoptera: Aphididae) Herbivory in Preconditioned Resistant and Susceptible near Isogenic Plants of Wheat

Interactions between biotype E greenbugs, Schizaphis graminum (Rodani), and two near isogenic lines of the greenbug resistance gene Gb3 of wheat, Triticum aestivum L., were examined for 62 d after infestation. By comparing aphid performance and host responses on control and greenbug-preconditioned plants, we demonstrated that systemic resistance to greenbug herbivory was inducible in the resistant genotype with varying intensities and effectiveness in different parts of the plants. Preconditioning of susceptible plants resulted in modification of within-plant aphid distribution and reduction of cumulative greenbug densities, but it showed no effect on reducing greenbug feeding damage to host plant. Preconditioning of resistant plants altered greenbug population dynamics by reducing the size and buffering the fluctuation of the aphid population. Preconditioning in the first (oldest) leaf of the resistant plant had no phenotypically detectable effect in the stem and induced susceptibility locally in the first leaf within the first 2 d after infestation. The preconditioning-induced resistance reduced greenbug density, delayed aphid density peaks and extended the life of younger leaves in resistant plants. Expression of induced resistance was spatially and temporally dynamic within the plant, which occurred more rapidly, was longer in duration, and stronger in intensity in younger leaves. Host resistance gene-mediated induced resistance was effective in lowering greenbug performance and reducing damage from greenbug herbivory in host plants. Results from this study supported the optimal defense theory regarding within-plant defense allocation.

Effect of greenbugs (Homoptera: Aphididae) on yield loss of winter wheat.

The effect of greenbug, Schizaphis graminum (Rondani), feeding on the yield of four winter wheat cultivars commonly grown in Oklahoma was studied. Cultivars tested were 'Karl', a recent derivative 'Karl-92', and '2163', all greenbug-susceptible cultivars; and 'TAM-110', a cultivar with resistance to biotype E greenbugs. The objectives were to determine the effect of different greenbug densities during fall and spring on yield of winter wheat, and to develop mathematical models to quantify the effect of greenbugs on yield loss. The intensity of greenbug infestations achieved in plots by artificial infestation varied among years and growing seasons within a year, but was generally sufficient to cause a reduction in yield. Among yield components, the number of heads per square meter and the number of seeds per head were frequently negatively correlated with the accumulated number of greenbug-days per tiller. Seed weight was rarely affected by greenbug infestation. A regression model estimated yield loss for greenbug-susceptible cultivars at 0.51 kg/ha loss of yield per greenbug-day in years with near normal precipitation, and a loss of 1.17 kg/ha under severe drought conditions. The susceptible winter wheat cultivars exhibited similar yield loss in relation to the intensity of greenbug infestation, as indicated by a common slope parameter in the regression model. Results suggest that the model is robust for predicting yield loss for susceptible cultivars.

Greenbug Resistance Management on Sorghum with Insecticide Mixtures: a Biological and Economic Analysis

Several tactics were evaluated for insecticide resistant greenbug, Schizaphis graminum (Rondani), control on sorghum. During the first 2 yr of this research, control by chlorpyrifos, carbofuran, and malathion and mixtures of the latter 2 chemicals plus piperonyl butoxide with chlorpyrifos were compared on sorghum. Chlorpyrifos provided <60% control. The mixtures of chlorpyrifos + carbofuran or malathion provided good control of insecticide resistant greenbug. The mixture of chlorpyrifos + piperonyl butoxide provided mediocre control of resistant greenbugs. In 1996, an experiment was designed to evaluate the effects of greenbug population insecticide resistance ratio and preexposure of greenbugs to chlorpyrifos on control by mixtures of chlorpyrifos with carbofuran or malathion. About half of the plots were presprayed with chlorpyrifos (0.28 kg [AI]/ha) 4 d before applying individual insecticides or mixtures. Plots were infested with 2 ratios of resistant: susceptible greenbugs (1:3 and 3:1, respectively). Application of mixtures of chlorpyrifos + malathion provided best control followed by chlorpyrifos + carbofuran and chlorpyrifos. Prespraying greenbugs with chlorpyrifos did not affect their control with subsequent insecticide resistance management mixtures. The difference between the 2 ratios was significant with the lowest greenbug densities in plots dominated by susceptible individuals. There was a significant yield response to greenbug densities. The highest yields were obtained in plots sprayed with chlorpyrifos + malathion mixtures. When chlorpyrifos was applied to greenbug populations dominated by resistant aphids, yields were lower than in the infested control plots where greenbugs were not sprayed. Economic analysis of the data further demonstrated the advantage of the chlorpyrifos + malathion mixture for controlling insecticide resistant greenbug.

Greenbug (Homoptera: Aphididae) Feeding Effects on Nonstructural Carbohydrates in Sorghum

The effects of greenbug, Schizaphis graminum (Rondani), feeding on the nonstructural carbohydrate concentrations of field-grown seedling and vegetative sorghum plants, Sorghum bicolor Moench, were measured by high-performance liquid chromatography. Four individual experiments were completed for each of the plant growth stages to compare nonstructural carbohydrate concentrations between greenbug-infested and uninfested plants. Greenbug-infested seedling plants tended to have greater concentrations of nonstructural carbohydrates in the shoots and lower concentrations in the roots when compared with uninfested plants. The concentration of sucrose in the shoots of seedling plants increased and starch in the roots decreased in a linear relationship with increasing greenbug density. In contrast to seedling plants, roots of greenbug-infested vegetative plants had a greater concentration of total nonstructural carbohydrates and shoots had a reduced concentration. The starch concentration in the shoots of infested vegetative plants decreased with increasing greenbug density. These results demonstrate that sorghum plants at these two growth stages respond differently to greenbug feeding in their ability to maintain nonstructural carbohydrate concentrations.

Greenbug Control in Winter Wheat with Seed Treatments and Granular Insecticides, 1991-1992:

Abstract NTN 33989 (imidacloprid) was evaluated for greenbug control in winter wheat planted at the following 3 locations and dates in north central TX: Dallas Co. on 11 Nov, Cooke Co. on 26 Nov and Collin Co. on 15 Nov. Soil types were as follows: Dallas Co., Austin silty clay, pH ,= 7.8; Collin and Cooke Co., Houston black clay, pH = 7.8. Wheat seed treated with NTN 33893 75WS was provided by Gustafson, Inc. Disyston 15G was used as a standard. Both granular insecticides were mixed with the seed and applied in-furrow. All wheat seed used in the trial was from the same lot. Plots measured 6 X 20 ft and were arranged in a RCB design with 4 replications. Plots were planted with a small plot planter at a rate of 80 lb of seed/acre. Seventeen inches of rain fell after planting through February with a total of 40 days of rain. Greenbug infestations did not develop in the test plots because of these rains. Also, greenbug parasites and predators were active throughout the mild winter and further reduced greenbug densities. To assess insecticide activity, a 2 inch diam plug of wheat plants was dug from each of the center 2 drill rows of each plot and potted in a 2.5 X 2.5 inch plastic pot. Pots were infested with greenbugs obtained from a laboratory colony which originated from the test region. Greenbugs were applied with a hand held inoculator calculated to deliver 30 greenbugs per pot. Infested pots were held in an incubator at 70° F for 7-10 d at which time the greenbugs in each pot of wheat were counted. Each test location was sampled once.

Outbreaks of Banks Grass Mite (Acari: Tetranychidae) in Grain Sorghum Following Insecticide Applications

Banks grass mite, Oligonychus pratensis (Banks), abundance was monitored in grain sorghum (Sorghum bicolor (L.) Moench) to determine if applications of insecticides directed at green bug, Schizaphis graminum (Rondani), induced outbreaks of Banks grass mites. Aerial applications of two commonly used insecticides, chlorpyrifos (0.28 kg [AI]/ha) and parathion (0.67 kg [AI]/ha), and an untreated check were replicated three times and repeated during each of 3 yr. In each test, mite densities were higher in insecticide-treated sorghum than in untreated sorghum. Data subjected to analysis of covariance (with pretreatment mite numbers used as the covariate) indicated that mite densities were significantly higher in insecticide-treated sorghum than in untreated sorghum. but that mite densities in chlorpyrifos- or parathion-treated sorghum, did not differ significantly. Mite predators per 1,000 mites were not significantly lower in insecticide-treated sorghum than in untreated sorghum. Both insecticides were effective in reducing green bug densities.

Experimental Evaluation of Predators and Parasitoids in Suppressing Greenbugs (Homoptera: Aphididae) in Sorghum and Wheat

The effectiveness of endemic predators and parasitoids as biological control agents of the greenbug, Schizaphis graminum (Rondani), was experimentally evaluated during 1985 and 1986 in Kansas winter wheat, Triticum aestivum , and grain sorghum, Sorghum bicolor. Mechanical exclusion was used as the experimental method of evaluation. The coccinellids Coleomegilla maculata lengi Timberlake, Hippodamia convergens Guerin, and Scymnus spp. were the predominant predators of greenbugs in sorghum and comprised 89% of the predator population. Lysiphlebus testaceipes (Cresson) was the most abundant primary parasitoid in sorghum. The natural enemy complex was able to suppress experimental greenbug densities at all stages of sorghum growth from 3-leaf through the boot stage. The impact of L., testaceipes on greenbugs was sporadic between locations. In winter wheat, H. convergens was the most abundant natural enemy and significantly suppressed greenbug densities. Natural enemies, primarily coccinellids, consistently reduced experimental greenbug populations in winter wheat and grain sorghum.

Damage by Greenbug (Homoptera: Aphididae) to Grain Sorghum as Affected by Tillage, Surface Residues, and Canopy1

Different cropping systems for grain sorghum were studied at two Texas locations and one Nebraska location to determine effects of tillage practice, cropping systems, crop residues, and plant canopy on greenbug, Schizaphis graminum (Rondani), abundance and crop damage. In each case, reduced tillage or crop residues on the soil surface (or both) resulted in a decreased number of greenbugs and amount of plant injury. In one study, a greenbug-resistant grain sorghum hybrid conventionally tilled was more severely damaged than a susceptible hybrid planted in a no-tillage situation, indicating the negative effect of reduced tillage on greenbug abundance. Influence of reduced tillage on green bug density occurred on plants in plots as large as 2.8 ha. In one grain sorghum field, a dense canopy of a weedy grass that obscured furrows substantially reduced greenbug infestation. In other fields, independent of surface residues and canopy, greenbugs seemed to distinguish between amount of cultivation and preferred plants growing in soil with the greatest amount of disturbance. Apparently, green bugs respond to background conditions of the host plant associated with tillage operations and seem to be repelled by crop residues, canopy, and the reduced tilled soil surface.

Beneficial role of corn leaf aphid, Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae), in maintaining Hippodamia spp. (Coleoptera: Coccinellidae) in grain sorghum

The significance of corn leaf aphid, Rhopalosiphum maidis (Fitch), as a food source for the natural enemies of greenbug, Schizaphis graminum (Rondani), was determined in the Texas High Plains sorghum agroecosystem. The most abundant coccinellid species were Hippodamia convergens (Guerin-Meneville) and H. sinuata (Mulsant). Neither coccinellid species showed any preference for either greenbug or corn leaf aphid in replicated choice predation tests. Corn leaf aphid and coccinellid densities increased at similar rates in the early season during both 1982 and 1983. Regression analyses suggested that variation in corn leaf aphid and greenbug densities significantly contribute to the variation in coccinellid densities. Furthermore, corn leaf aphid and coccinellid densities were significantly and positively correlated prior to sorghum panicle emergence. However, after panicle emergence only greenbug and coccinellid densities were highly correlated, reflecting a change in coccinellid food source from primarily corn leaf aphids to greenbugs. The ability of coccinellids to regulate greenbug densities may be largely dependent on the abundance of corn leaf aphids as a food source during early season crop growth.

Insect-Plant Interactions: Greenbugs (Homoptera: Aphididae) Disrupt Acclimation of Winter Wheat to Drought Stress

This growth-chamber study was designed to investigate the effect of greenbug, Schizaphis graminum (Rondani), feeding on physiological responses of wheat, Triticum aestivum L., associated with drought stress, to determine how drought stress affects greenbug density, and to determine how drought- and greenbug-resistant cultivars alter responses. The cultivars chosen were ‘Amigo’ (relatively resistant to biotype C greenbugs), ‘Sturdy’ (comparatively drought and greenbug susceptible), and ‘TAM W-101’ (comparatively drought resistant and greenbug susceptible). Greenbugs altered two potentially adaptive responses of wheat to drought; they virtually negated an increase in cell membrane stability associated with wheat conditioned to drought stress, and solute potential was reduced less in greenbug plus drought stress treatments than in drought stress-only treatments; water potential, however, was not altered by greenbug infestations. The lowered turgor pressure that resulted for infested plants suggests that osmotic adjustment (the maintenance of turgor through the accumulation of solutes in plants under drought stress) was also reduced by greenbugs. In addition, greenbug density (number of greenbugs per mg shoot dry weight) was greater on drought-stressed plants. These data provide physical and physiological evidence supporting field observations that greenbug infestations are potentially more damaging when wheat is subjected to drought than when rainfall is sufficient.

Role of Indigenous Coccinellids in Regulating Greenbugs (Homoptera: Aphididae) on Texas Grain Sorghum

The effectiveness of the native coccinellid predators of the greenbug, Schizaphis graminum (Rondani), was determined in Texas high plains grain sorghum using exclusion techniques. The most abundant greenbug predators encountered were Hippodamia convergens (Guerin-Meneville) and H. sinuate (Mulsant). Natural enemies showed no significant suppressive capacity during the early portion of the growing season, though both Hippodamia species were frequently observed. Selective exclusion of adult Hippodamia spp. and larger predators demonstrated the efficacy of these enemies throughout the latter portion of the growing season. Introduction of the two coccinellid species into cages excluding all enemies indicated their capacity to reduce greenbug density in light or moderate greenbug infestations. Regulation of greenbugs in Texas high plains grain sorghum is largely due to the suppressive action of Hippodamia spp., not the common greenbug parasites of the region.

Nitrogen Fertilizer Influence on Greenbug (Homoptera: Aphididae) Dynamics and Damage to Sorghum1

Green bug, Schizaphis graminum (Rondani), densities decreased in direct relationship to nitrogen (N) fertilizer rate (0, 45, 90, 135, 180, and 225 kg N/ha) and to increase in plant dry matter. Damage ratings related to green bug density indicated that N fertilizer did not alter natural sorghum tolerance to greenbugs. Greenbug dynamics responded in a positive manner to NH4+-N content in leaves. These data indicate that increasing N fertilizer enhanced sorghum fitness as a green bug host. However, the rate of aphid increase diminished at the higher N concentrations.

Schizaphis graminum 1 : Effect on Grain Sorghum Exposed to Severe Drought Stress 23

During extreme drought in eastern Nebraska in 1974 in which only 1.57 cm of rain fell from June 11 to Aug. 9, differences of 1274 and 991 biotype C greenbugs/plant caused significant yield reductions of 365 and 757 kg/ha respectively on grain sorghum in 2 field tests. These yield losses were 3 and 6 times greater than the then current loss associated with the economic injury level (121 kg/ha). Greenbug densities on the 3 dates of insecticide application and at peak density were significantly (P = 0.05) and inversely related to the numbers of heads in both tests.