Larry D. Godfrey

Midseason pest status of the cotton aphid (Homoptera : Aphididae) in California cotton : Is nitrogen a key factor?

Abstract Field experiments were conducted from 1996 to 1998 to assess the effects of nitrogen fertilization rates and planting dates on the population dynamics of the cotton aphid, Aphis gossypii Glover, during the midgrowing season of California cotton. Cotton aphids reached higher densities in high nitrogen fertilized plants (227 kg N/ha, rate currently used by cotton growers) than in low nitrogen fertilized plants (57 kg N/ha). In addition, late-planted cotton (May–June), which had more nitrogen content, also harbored higher aphid populations than early plantings (April). Overall, aphid abundance was positively correlated with plant nitrogen content. In a moderate aphid pressure year (1996), planting the cotton early (April) was effective in keeping the aphid population below the midseason economic threshold. However, in a high aphid pressure year (1997), it was necessary to drastically reduce the nitrogen fertilization to 57 kg N/ha to maintain the aphid density under this threshold. Recent cultural practices in California cotton include higher rates of nitrogen fertilization, which increases nitrogen content of plants. The current data suggest that this practice (i.e., high fertilization) is an important factor contributing to the increased severity of the cotton aphid as a pest of California cotton during the midseason.

Remote Sensing for Detection of Cotton Aphid– (Homoptera: Aphididae) and Spider Mite– (Acari: Tetranychidae) Infested Cotton in the San Joaquin Valley

Abstract We explored remote sensing methods for their potential to distinguish aphid- (Aphis gossypii Glover) and spider mite–infested (Tetranychus spp.) cotton (Gossypium hirsutum L.) from uninfested cotton. Field plots were established using selective and disruptive pesticides to establish a range of aphid and mite populations over 2 yr. Aerial and satellite remote sensing data in 2003 and 2004 were supplemented with ground-based remote sensing data in 2004 and by ground-truthing of arthropod populations in both years. Mite- and aphid-infested cotton was detected using aerial data in the green and near-infrared (NIR) wavelengths in 2003, with subeconomic threshold aphid population levels. At the time aerial data were collected, mite populations peaked at 95% leaves infested and exceeded treatment threshold levels of 30–50% leaves infested. However, the number of mites per leaf in the treatments was low to moderate (32, 9, 4, 6, and 2 average mites/leaf). Moreover, cotton infested with cotton aphids above economic threshold levels was consistently detected using NIR wavelengths from the satellite data in 2004. Similarly, aphid-infested cotton was detected at both sub- and supraeconomic threshold aphid levels using NIR wavelengths from the ground-based remote sensing data. Finally, accumulated mite-days were linearly correlated with a canopy, false color, and a vegetation index using satellite data in 2004. Wavelengths in the NIR were fair to moderately accurate predictors of aphid- and mite-infested cotton.

Jasmonic Acid: A Vaccine Against Leafminers (Diptera: Agromyzidae) in Celery

Abstract Plant resistance to herbivores can be induced by application of elicitors such as jasmonic acid, which is a signal molecule that increases naturally in plants that have been damaged. The use of elicitors to induce resistance of crop plants against herbivores has been successful in small scale experiments but has not been developed in commercial agriculture. We tested jasmonic acid sprays as elicitors of resistance against leafminers and other pests on commercial celery fields in the central coast region of California. In two of three trials, significantly fewer leafminer adults emerged from the plants sprayed with jasmonic acid than the plants that were left untreated. In these two trials, aphid control was erratic, and thrips were not significantly reduced on the treated plants although thrips were not common during the trials. Leafminer parasitoid population densities tracked the number of available leafminer hosts regardless of treatment. The only effect found in the third trial was that conventionally grown celery had more leafminer oviposition stings than either the plants treated with jasmonic acid or untreated control plants. Treatment of plants with jasmonic acid seems to hold promise as an alternative pest management tool.

Spectral Response of Cotton Aphid– (Homoptera: Aphididae) and Spider Mite– (Acari: Tetranychidae) Infested Cotton: Controlled Studies

Abstract Remote sensing is a precision tool that can detect plant health. Ground-based methods in small-scale experiments were used to explore the applicability of this technology for detection of arthropod-damaged cotton and to find useful indices or wavelengths for detecting arthropod-damaged cotton. Individual leaves of greenhouse-grown cotton plants and cotton plants in the field were infested with populations of cotton aphids, spider mites, and aphids + mites. Several sets of reflectance measurements were collected from the adaxial surface of the leaves at various intervals after infestation using a portable hyperspectral spectrometer with an integrating sphere or a contact probe. Vegetation indices were calculated from the reflectance values; these indices and the raw reflectance values, represented by narrow wavelength bands, were tested to see if arthropod damaged cotton could be distinguished from healthy cotton. Results indicated that it was possible to detect cotton aphid– and spider mite–damaged leaves by tracking the spectral changes in the leaf, although the damage type of each arthropod could not be distinguished spectrally. In addition, spider mite– and aphid-infested cotton leaves increased reflectance in the near infrared wavelength at ≈850 nm in comparison to uninfested leaves.

Interactions Between the Augmentatively Released Predaceous Mite Galendromus occidentalis (Acari: Phytoseiidae) and Naturally Occurring Generalist Predators

Abstract Predatory mite releases can be an effective means of managing spider mites in many perennial cropping systems, yet little research has been performed in annual cropping systems. Herein we evaluate the compatibility of predaceous mite releases with the conservation of resident natural enemies in an annual agroecosystem. We quantify the impact of naturally occurring generalist predators, Geocoris spp. and Orius tristicolor White, and the omnivore Frankliniella occidentalis (Pergande), on the establishment of the western predatory mite Galendromus occidentalis (Nesbitt) and how these predator-predator interactions influence spider mite control. Field experiments showed that in the absence of generalist predators, released predatory mites can establish populations on cotton, increase in abundance through reproductive recruitment, and suppress spider mite populations. Hemipteran predators had a negative impact on predatory mite populations but generally improved spider mite suppression. The presence of F. occidentalis had no impact on predatory mite performance.

Remotely sensing arthropod and nutrient stressed plants: a case study with nitrogen and cotton aphid (Hemiptera: Aphididae).

ABSTRACT Remote sensing can be used in combination with ground sampling to detect aphid(Aphis gossypii Glover) infested cotton (Gossypium hirsutum L.). Changes in wavelengths in the near-infrared (NIR) have proven useful for such detection, but these changes can be confused with other factors stressing plants, such as water deficiency and nutrient status. This study was designed to test the utility of this technology to distinguish between two factors stressing plants: nitrogen deficiency and aphids. Field plots were created by applying varying rates of nitrogen to cotton at different dates in the growing season in 2003 and 2004. Subplots were created by applying disruptive insecticides, which increased aphid populations in a portion of the subplots. Airplane and satellite remote sensing data in 2003 and 2004 were supplemented with ground sampling of aphid populations in both years. Insecticide application, nitrogen application rate and date influenced aphid abundance. Cotton with higher aphid populations could be distinguished from cotton with natural aphid infestations independent of plant nitrogen status using a NIR wavelength in 2003 and a proprietary 2004 index. Complex distinctions among varying nitrogen treatments and aphid abundance were not possible using this data. In the future, possible confounding factors should be investigated from the perspective of their change on crop physiology before remote sensing can be used in an integrated pest management (IPM) program.

A Century of Rice Water Weevil (Coleoptera: Curculionidae): A History of Research and Management With an Emphasis on the United States

The rice water weevil ( Lissorhoptrus oryzophilus Kuschel) is a native curculionid pest of rice in the southern and eastern United States. It was first identified as Lissorhoptrus simplex Say in the first report of damage from southern Georgia in 1881. In 1951 Chilean systematist Giullermo Kuschel reclassified it as L. oryzophilus following a reevaluation of New World genera within Curculionidae. Management of the weevil has changed throughout the years, as environmental issues, regulatory actions, and pesticide resistance have required researchers, pest management practitioners, and growers to adapt. In the 2010s, management of the rice water weevil has expanded with the use of anthralic diamides and neonicotinoids as the latest conventional options, generally delivered as seed treatments in southern U.S. rice production, and the possible emergence of Bacillus thuringiensis as a viable alternative to chemical controls. Delayed flooding and planting are common cultural controls used in southern U.S. rice production while levee weed control and winter flooding are used in California production. The history of this insect pest including management, life history, and invasion biology in rice production regions of the temperate world will be discussed with an emphasis on the United States.

Thresholds, Injury, and Loss Relationships for Thrips in Phleum pratense (Poales: Poaceae)

ABSTRACT Timothy (Phleum pratense L.) is an important forage crop in many Western U.S. states. Marketing of timothy hay is primarily based on esthetics, and green color is an important attribute. The objective of these studies was to determine a relationship between arthropod populations, yield, and esthetic injury in timothy. Economic injury levels (EILs) and economic thresholds were calculated based on these relationships. Thrips (Thripidae) numbers were manipulated with insecticides in small plot studies in 2006, 2007, and 2008, although tetranychid mite levels were incidentally flared by cyfluthrin in some experiments. Arthropod population densities were determined weekly, and yield and esthetic injury were measured at each harvest. Effects of arthropods on timothy were assessed using multilinear regression. Producers were also surveyed to relate economic loss from leaf color to the injury ratings for use in establishing EILs. Thrips population levels were significantly related to yield loss in only one of nine experiments. Thrips population levels were significantly related to injury once before the first annual harvest and twice before the second. Thrips were the most important pest in these experiments, and they were more often related to esthetic injury rather than yield loss. EILs and economic thresholds for thrips population levels were established using esthetic injury data. These results document the first example of a significant relationship between arthropod pest population levels and economic yield and quality losses in timothy.

Spatial Dependence, Dispersion, and Sequential Sampling of Anaphothrips obscurus (Thysanoptera: Thripidae) in Timothy

ABSTRACT The spatial distribution and dispersion of Anaphothrips obscuras (Müller) (Thysanoptera: Thripidae) was examined with the goal of establishing a sequential sampling plan for this pest in timothy, Phleum pratense L. (Poaceae). Approximately 16 different California timothy fields were sampled twice yearly from 2006 to 2008 using direct observation and the beat cup method. For direct observation, the number of thrips on each leaf of the plant was counted. For the beat cup method, tillers were tapped into a cup and dislodged thrips were counted. Samples were separated by ∼3 m in 2006 and 2007 and exactly 3 m in 2008. Spatial autocorrelation of intrafield population distribution was tested for significance in 2008 using Morans I, but autocorrelation was not detected. The population dispersion was assessed by Taylors power law and was determined to be aggregated and density-dependent. Intraplant population dispersion and distribution for each year were also evaluated for adults, larvae, and total thrips. All lifestages were highly spatially dependent and more thrips were found near the top of the plant than the bottom. Direct observation proved to be a more accurate and precise method than the beat cup method, especially when thrips abundances were greater than one. However, the number of samples required to provide an accurate level of precision was unrealistic for both methods. A sequential sampling plan was evaluated, but was not practical for the beat cup method because few thrips were found using this method. Because there was no spatial autocorrelation at sampling distances of 3 m, samples can be taken at intervals at 3 m to obtain spatially independent population abundance estimates.

Characterization of an EPG Waveform Library for Adult Lygus lineolaris and Lygus hesperus (Hemiptera: Miridae) Feeding on Cotton Squares

Abstract Lygus lineolaris (Palisot de Beauvois) and Lygus hesperus Knight are among the most important pests affecting production of cotton in the United States. Lygus spp. use a cell rupture feeding strategy. However, the precise stylet-probing behaviors of adult Lygus spp. are not well understood or quantifiably related to cotton damage. The long-term goals of our research are to: 1) relate stylet probing to damage, and 2) quantitatively compare L. lineolaris feeding among resistant and susceptible host plants. The specific objectives of this study were to apply the latest technology in electropenetrography (EPG) to record adult, prereproductive Lygus spp. feeding, to identify and characterize all the waveforms, and to hypothesize their biological meanings. We used a third-generation AC–DC electropenetrograph to record nonprobing and probing waveforms of adult bugs on pinhead (<3 mm) cotton squares, and constructed a waveform library from the output. Recordings were obtained with both AC and DC applied signals and at different input impedances (106–109 Ω). Three nonprobing waveforms were identified and visually correlated: Standing still (S), walking (W), and antennation (A). Probing waveforms were classified as: cell rupturing (CR), transition (T), and ingestion (I). T waveform is the first finding of an X wave for a nonsalivary sheath feeder in Hemiptera, implying that tasting/testing/acceptance behaviors can be performed by a cell rupture feeder. While waveform I is not performed in every probe, when performed, its appearance and structure were affected by applied signal and input impedance. Overall, time spent in nonprobing behaviors was longer than time spent on probing behaviors.