Monitoring the health of Huanglongbing-affected citrus trees by following changes in leaf Candidatus Liberibacter asiaticus (CLas) titer has an inherent element of imprecision because CLas titer varies considerably within the tree canopy... more
Monitoring the health of Huanglongbing-affected citrus trees by following changes in leaf Candidatus Liberibacter asiaticus (CLas) titer has an inherent element of imprecision because CLas titer varies considerably within the tree canopy and with calendar seasons. In addition, the destructive sampling method used to determine CLas titer entails a different set of leaves per sampling period adding to the inconsistency and inexactitude of the results. To overcome these ambiguities and to reduce the numerical variability between samples, we developed an experimental method that analyzes portions of the same treated leaves for up to four sampling periods. By assaying subsamples of adjacent locations of the same leaf, random variability was significantly reduced, and comparative analysis can be carried out with greater precision.
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Under specific conditions, the fruit on citrus trees will split open. The damaged fruit is unmarketable and provides a habitat for fungal and insect pests that can reproduce and then damage currently marketable fruit. Losses of 30 to over... more
Under specific conditions, the fruit on citrus trees will split open. The damaged fruit is unmarketable and provides a habitat for fungal and insect pests that can reproduce and then damage currently marketable fruit. Losses of 30 to over 50 percent of the crop are possible with some cultivars. This is a physiological disorder that starts with nutrient imbalances at flowering that result in mechanically weak areas in the rind. These rupture if interior parts of the fruit expand faster than the peel can stretch. The disconnect between problem initiation and symptom expression provides many challenges to experimental designs and interpretation. Consequently, no solution has been found despite over a century of research into the problem. This is also a problem for growers because they can only see the problem after it is too late to correct. Our goal is to define the problem and highlight successes and failures in finding a solution. The review should help direct continuing research an...
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Huanglongbing is a citrus disease that reduces yield, crop quality, and eventually causes tree mortality. The putative causal agent, Candidatus Liberibacter asiaticus (Rhizobiales: Rhizobiaceae), is vectored by the Asian citrus psyllid,... more
Huanglongbing is a citrus disease that reduces yield, crop quality, and eventually causes tree mortality. The putative causal agent, Candidatus Liberibacter asiaticus (Rhizobiales: Rhizobiaceae), is vectored by the Asian citrus psyllid, Diaphorina citri Kuwayama. Disease management is largely through vector control, but the insect is developing pesticide resistance. A nonchemical approach to vector management is to grow citrus under screen cages either as bags over individual trees or enclosures spanning many acres. The enclosing screen reduces wind, alters temperature relative to ambient, and excludes a variety of pests that are too large to pass through the screen. Here we evaluated the potential of six screens to exclude D. citri. We conclude that screens with rectangular openings need to limit the short side to no more than 384.3 µm with a SD of 36.9 µm (40 mesh) to prevent psyllids from passing through the screen. The long side can be at least 833 µm, but the efficacy of screen...
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ABSTRACTCandidatus Liberibacter asiaticus is vectored by the psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) and putatively causes Huanglongbing disease in citrus. Huanglongbing has reduced yields by 68% relative to pre-disease... more
ABSTRACTCandidatus Liberibacter asiaticus is vectored by the psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) and putatively causes Huanglongbing disease in citrus. Huanglongbing has reduced yields by 68% relative to pre-disease yields in Florida. Disease management is partly through vector control. Understanding vector biology is essential in this endeavor. Our goal was to document differences in probing behavior linked to sex. Based on both a literature review and our results we conclude that there is either no effect of sex or that identifying such an effect requires a sample size at least four times larger than standard methodologies. Including both color and sex in statistical models did not improve model performance. Both sex and color are correlated with body size, and body size has not been considered in previous studies on sex in D. citri. An effect of body size was found wherein larger psyllids took longer to reach ingestion behaviors and larger individuals spent mo...
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The invasive Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), is the primary vector of the phloem-infecting bacterium, Candidatus Liberibacter asiaticus. Candidatus L. asiaticus is the putative causal agent of Huanglongbing... more
The invasive Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), is the primary vector of the phloem-infecting bacterium, Candidatus Liberibacter asiaticus. Candidatus L. asiaticus is the putative causal agent of Huanglongbing (HLB) disease, a destructive disease of Citrus. While many Citrus species are susceptible to D. citri probing and HLB disease, there are marked behavioral differences in D. citri probing responses and Ca. Liberibacter asiaticus infection severity among Citrus species. Using four mandarin hybrid selections and pummelo plants variably resistant to D. citri probing, oviposition, and survival, we explored probing differences using electropenetrography (EPG), conducted an oviposition and survival study, and determined host plant metabolites using gas-chromatography mass-spectroscopy (GC-MS). We found thirty-seven D. citri probing variables to be significantly different among tested mandarin selections and pummelo, in addition to differential oviposition a...
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Insects can be effective vectors of plant diseases and this may result in billions of dollars in lost agricultural productivity. New, emerging or introduced diseases will continue to cause extensive damage in afflicted areas.... more
Insects can be effective vectors of plant diseases and this may result in billions of dollars in lost agricultural productivity. New, emerging or introduced diseases will continue to cause extensive damage in afflicted areas. Understanding how the vector acquires the pathogen and inoculates new hosts is critical in developing effective management strategies. Management may be an insecticide applied to kill the vector or a host plant resistance mechanism to make the host plant less suitable for the vector. In either case, the tactic must act before the insect performs the key behavior(s) resulting in either acquisition or transmission. This requires knowledge of the timing of behaviors the insect uses to probe the plant and commence ingestion. These behaviors are visualized using electropenetrography (EPG), wherein the plant and insect become part of an electrical circuit. With the tools to define specific steps in the probing process, we can understand the timing of acquisition and ...
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Apple (Malus domestica Borkh.) leaves were sprayed to runoff using a selection of pesticides, and subsequent spray retention was evaluated by weight. Timing, cultivar, leaf surface, and leaf type significantly influenced spray retention.... more
Apple (Malus domestica Borkh.) leaves were sprayed to runoff using a selection of pesticides, and subsequent spray retention was evaluated by weight. Timing, cultivar, leaf surface, and leaf type significantly influenced spray retention. Spray retention correlated significantly and positively with leaf hair density. The importance of these differences is considered in relation to the possible efficiency of the pesticide application process in apple orchards.
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is a major pest of citrus because it transmits Liberibacter asiaticus, a phloem-limited bacterium that putatively causes Huanglongbing (HLB). The disease moves slowly through a tree, and the vector facilitates further within-tree movement... more
is a major pest of citrus because it transmits Liberibacter asiaticus, a phloem-limited bacterium that putatively causes Huanglongbing (HLB). The disease moves slowly through a tree, and the vector facilitates further within-tree movement via transmission of the pathogen. However, this only happens when stylets contact the phloem, to inoculate bacteria during phloem salivation and acquire bacteria during phloem sap ingestion. Behavioral changes in associated with different plant parts would affect how long it takes to reach phloem and how long the psyllids stays in phloem to ingest, thereby influencing the risk of disease spread. feeding was recorded on the abaxial and adaxial surfaces of mature and immature citrus leaves. Adults in the field can be found on these surfaces at all times of year. On abaxial surface of immature leaves, phloem salivation would occur after 11 h on average, but rarely as soon as 0.56 h. The corresponding values on mature leaves were 16 and 2.7. In general...
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Electropenetrography a.k.a. electrical penetration graph or EPG is a rigorous technique for studying arthropod behavior. Essentially, the arthropod and host are part of an electrical circuit that generates patterns of voltage (waveforms),... more
Electropenetrography a.k.a. electrical penetration graph or EPG is a rigorous technique for studying arthropod behavior. Essentially, the arthropod and host are part of an electrical circuit that generates patterns of voltage (waveforms), whose biological meanings are defined by correlation with histology and behavior. EPG is used for studying stylet probing behavior of hemipterans, and blood-feeding arthropods. These results are applied to understanding pesticide action, host plant resistance, and vector-pathogen-host interactions. At the end of all recordings, the arthropod begins a behavior that ends because the scientist stopped recording. An argument for keeping this event in the data has been made based on the assumption that the insect is adapting to laboratory conditions. In this adaptation process, the expected durations of ingestion behaviors will increase as the insect adapts. We show that this assumption can cause problems in data analysis and interpretation of the data....
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Insect-transmitted plant-pathogenic bacteria may alter their vectors' fitness, survival, behavior, and metabolism. Because these pathogens interact with their vectors on the cellular and organismal levels, potential changes at the... more
Insect-transmitted plant-pathogenic bacteria may alter their vectors' fitness, survival, behavior, and metabolism. Because these pathogens interact with their vectors on the cellular and organismal levels, potential changes at the biochemical level might occur. “ Candidatus Liberibacter asiaticus” ( C Las) is transmitted in a persistent, circulative, and propagative manner. The genome of C Las revealed the presence of an ATP translocase that mediates the uptake of ATP and other nucleotides from medium to achieve its biological processes, such as growth and multiplication. Here, we showed that the levels of ATP and many other nucleotides were significantly higher in C Las-infected than healthy psyllids. Gene expression analysis showed upregulation for ATP synthase subunits, while ATPase enzyme activity showed a decrease in ATPase activity. These results indicated that C Las stimulated Diaphorina citri to produce more ATP and many other energetic nucleotides, while it may inhibit ...
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Adults, immatures and eggs of Tuckerella japonica (Ehara) were collected from unknown clones or varieties of Camellia sinensis (L.) O. Kuntze tea bushes in the Clemson University Farm, Coastal Research and Education Center, Charleston,... more
Adults, immatures and eggs of Tuckerella japonica (Ehara) were collected from unknown clones or varieties of Camellia sinensis (L.) O. Kuntze tea bushes in the Clemson University Farm, Coastal Research and Education Center, Charleston, South Carolina; from Assam hybrids in The Caw Caw Nature Preserve in Ravenel, SC; from C. sinensis and C. assamica (Masters) in the Charleston Tea Plantation on Wadmalaw Island, SC; C. sinensis in the Fairhope Tea Plantation in Fairhope, Alabama; and from C. sinensis 'Rosea' and a C. sinensis and C. assamica hybrid in Savannah and Ellabell, Georgia, between 1994 and 2015. This mite was consistently collected from 1-, 2- and 3+-year-old wood of tea plants with significantly greater numbers collected from 2-year-old wood. All stages of the mite were found within longitudinally split areas of the wood where underlying green bark tissues were exposed. As 1-year-old wood matured, there was increased splitting of the bark with increased mite presenc...
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ABSTRACT
Typescript (photocopy). Thesis (M.S.)--Colorado State University, 1990. Includes bibliographical references (leaves [36]-40).
Aphis gossypii Glover is a destructive pest of over two dozen crops world wide. Damage to a few of these crops is due to direct feeding, but for most of these crops its impact is through its role as a virus vector.As expected, this has... more
Aphis gossypii Glover is a destructive pest of over two dozen crops world wide. Damage to a few of these crops is due to direct feeding, but for most of these crops its impact is through its role as a virus vector.As expected, this has resulted in many articles dealing with methods of controlling this insect. The aphid has the ability to become resistant to many pesticides and there is growing concern over environmental impacts of pesticide use. As a result, manipulation of the agroecosystem will playan ever increasing role in the management of this insect. Most aspects of the biology of this aphid are covered in this review. The recurrent theme centers around the importance of host plant influences on the biology of the aphid. In addition to examining the literature on the biology of the aphid, a large section is devoted to organisms which influence mortality in the aphid, and to aphid borne viruses transmitted by this aphid. This review covers the literature from 1912 to 1995, but...
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THIS IS THE ENTIRE ARTICLE Candidatus Liberibacter asiaticus (Las) causes the insect vectored disease Huanglongbing (HLB) in Citrus spp. In Florida, the disease rate has increased two-fold every year since 2005. Significant knowledge gaps... more
THIS IS THE ENTIRE ARTICLE Candidatus Liberibacter asiaticus (Las) causes the insect vectored disease Huanglongbing (HLB) in Citrus spp. In Florida, the disease rate has increased two-fold every year since 2005. Significant knowledge gaps exist in Las transmission and epidemiology. Sweet orange groves in central Florida were selected to study seasonal dynamics of Las over a 3-yr period in host and vector (Asian citrus psyllid; ACP). Two to three hundred trees were selected in each grove and 1 leaf/tree was collected randomly every fortnight. Sample collection began in June 2010 with collections ongoing. For qPCR detection of Las, the midribs of 2–5 leaves were randomly pooled to obtain 30–40 samples/date. An estimated Las prevalence in the branches was calculated from the pools with PooledInfRate v3. Simultaneously, ACP collected from the same location were pooled at 1–6 ACP/sample for qPCR. Las prevalence increased in the moderately infected grove from summer to fall (25 to 36%) an...
Abstract: This article summarizes findings of a survey of agricultural producers concerning their practices and attitudes regarding pesticide spray drift. The results reveal that just as the agricultural enterprises involved in the sample... more
Abstract: This article summarizes findings of a survey of agricultural producers concerning their practices and attitudes regarding pesticide spray drift. The results reveal that just as the agricultural enterprises involved in the sample are diverse and complex, so too are the approaches that growers take to managing drift. Growers tend to use multiple strategies in approaching this problem and display flexibility in attempting to achieve drift reduction. At the same time, they are concerned about implications of drift reduction for farm profitability. Programs and regulations designed to reduce drift should be constructed in ways that allow growers to comply without bearing excessive costs. Article available at http://www.joe.org/joe/2008august/a8p.shtml
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ABSTRACT Monitoring feeding behaviors of insects whose piercing–sucking mouthparts are inserted into plant tissue is often done by making the insect part of an electronic circuit, using a technique called Electrical Penetration Graph, or... more
ABSTRACT Monitoring feeding behaviors of insects whose piercing–sucking mouthparts are inserted into plant tissue is often done by making the insect part of an electronic circuit, using a technique called Electrical Penetration Graph, or electropenetrography (both abbreviated EPG). Fluctuating voltage signals in the circuit are graphed, and resulting waveforms are interpreted by a researcher as specific stylet activities. After measurement of waveforms, data consist of a list of different behaviors and associated durations. These data are further processed to yield hundreds of variables that are compiled and statistically analyzed prior to publication. The goal of this study was to develop a program to make this process more efficient for studies of aphids and related species, given the large quantity of data expected to be generated. Herein, the three major existing programs that perform this function are reviewed. The oldest program (Backus 1.0) both compiles data and calculates a SAS-based statistical analysis; however it only works with the original, recorded variables and is not tailored to aphid studies. The other programs (EPG Calc and the Sarria Excel® workbook) compile a more diverse suite of derived variables suitable for aphids than does Backus 1.0; however, they do not include statistical analyses. A new program (Ebert 1.0) introduced herein uses SAS to calculate the diverse suite of derived variables for aphids, and also provides statistical analysis via powerful mixed-model ANOVA using a single software platform, similar to the Backus program. The code is open source, so that any researcher can adapt this program to deal with behavioral idiosyncrasies of a particular study insect. The new program will be especially valuable for large experiments with many insect subjects.
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One way to study hemipteran feeding behavior is by measuring voltage changes in an electrical circuit that includes the insect and plant, via an Electrical Penetration Graph (EPG) monitor. This procedure results in a recording of... more
One way to study hemipteran feeding behavior is by measuring voltage changes in an electrical circuit that includes the insect and plant, via an Electrical Penetration Graph (EPG) monitor. This procedure results in a recording of waveforms that represent stylet penetration events through time. One approach to analysis of these data is to select specific waveforms and calculate averages of their durations or frequencies, per event, per probe, or per individual insect. SAS statistical analysis programs have been developed to make such calculations. However, this approach ignores information contained in the often stereotypical, sequential ordering of waveform events. We show how SAS can be used to extract, average, and statistically test among biologically sequential variables such as "time to first phloem penetration" from standard EPG data files. We demonstrate the process using data from aphids and psyllids, and discuss both the advantages and limitations of using these n...
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ABSTRACT This paper presents the results of two related studies concerning the aerial application of dispersants. The first study characterized the interactions of various sized Corexit 9500 and 95...
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Experiments on the biological consequences of differences in pesticide distribution include testing differences in application equipment, differences in formulation, and more direct tests of the influence of droplet size, droplet number,... more
Experiments on the biological consequences of differences in pesticide distribution include testing differences in application equipment, differences in formulation, and more direct tests of the influence of droplet size, droplet number, or application volume on efficacy for insecticides, herbicides, or fungicides applied as atomized sprays. While these tests have been conducted for at least 60 years, there are continued calls
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Abstract Aquatic beetles in the families Dryopidae, Dytiscidae, Elmidae, Gyrinidae, Haliplidae, Hydrophilidae, Noteridae, Psephenidae, and Scirtidae were sampled at the Ravenna Training and Logistics (RTLS) site in northeast Ohio from... more
Abstract Aquatic beetles in the families Dryopidae, Dytiscidae, Elmidae, Gyrinidae, Haliplidae, Hydrophilidae, Noteridae, Psephenidae, and Scirtidae were sampled at the Ravenna Training and Logistics (RTLS) site in northeast Ohio from 1999 through 2001. The site is a military base with restricted access, but military activities can cause considerable environmental disturbance. The RTLS has many headwater streams that are part of the Mahoning River basin. It is therefore an important resource in maintaining stream quality in this watershed. This survey is the first comprehensive effort at surveying the aquatic beetles at the RTLS. 124 species were collected including three haliplids, three dytiscids, one gyrinid, and three hydrophilids that were new state records for Ohio. We used these capture data to obtain preliminary estimates of biodiversity in different portions of the RTLS, and estimate how many species we missed in our sampling program. We estimated that about 90% of the total species present at the RTLS were recovered in this survey.