Lygus Hesperus Research Articles

A data‐driven, machine learning framework for optimal pest management in cotton

AbstractDespite the significant effects of agricultural pest management on crop yield, profit, environmental quality, and sustainability, farmers oftentimes lack data‐driven decision support to help optimize pest management strategies. To address this need, we curated a comprehensive data set that consists of pest, pest management, and yield information from 1498 commercial cotton crops in California's San Joaquin Valley between 1997 and 2008. Using this data set, we built a Markov decision process model to identify the optimal management policy of a key cotton pest, Lygus hesperus, that balances the tradeoff between yield loss and the cost of pesticide applications. Our results show that pesticide applications targeting L. hesperus are only economically optimal during the first 2 weeks of June, and pesticide applications were associated with increased risk of an unprofitable harvest. About 46% of the observations in our data set involved at least one pesticide application outside of this optimal window, demonstrating the need for a data‐driven approach to crop management. Sensitivity analyses on parameter perturbations and reduced data set sizes suggest that our methodology provides a robust policy‐making tool, even in noisy data sets.

ECDYSTEROID AND CHITINASE FLUCTUATIONS IN THE WESTERN TARNISHED PLANT BUG (Lygus hesperus) PRIOR TO MOLT INDICATE ROLES IN DEVELOPMENT.

Vital physiological processes that drive the insect molt represent areas of interest for the development of alternative control strategies. The western tarnished plant bug (Lygus hesperus Knight) is a pest of numerous agronomic and horticultural crops but the development of novel control approaches is impeded by limited knowledge of the mechanisms regulating its molt. To address this deficiency, we examined the fundamental relationship underlying the hormonal and molecular components of ecdysis. At 27°C L. hesperus exhibits a temporally controlled nymph-adult molt that occurs about 4 days after the final nymph-nymph molt with ecdysteroid levels peaking 2 days prior to the final molt. Application of exogenous ecdysteroids when endogenous levels had decreased disrupted the nymphal-adult molt, with treated animals exhibiting an inability to escape the old exoskeleton and resulting in mortality compared to controls. Using accessible transcriptomic data, we identified 10 chitinase-like sequences (LhCht), eight of which had protein motifs consistent with chitinases. Phylogenetic analyses revealed orthologous relationships to chitinases critical to molting in other insects. RT-PCR based transcript profiling revealed that expression changes to four of the LhChts was coordinated with the molt period and ecdysteroid levels. Collectively, our results support a role for ecdysteroid regulation of the L. hesperus molt and suggest that cuticle clearance is mediated by LhCht orthologs of chitinases that are essential to the molt process. These results provide the initial hormonal and molecular basis for future studies to investigate the specific roles of these components in molting.

Modelling populations of Lygus hesperus on cotton fields in the San Joaquin Valley of California: the importance of statistical and mathematical model choice

ABSTRACTUnderstanding the population dynamics of herbivorous insects is critical to developing and implementing effective pest control protocols. In the context of inverse problems, we explore the dynamic effects of pesticide treatments on Lygus hesperus, a common pest of cotton in the western United States. Fitting models to field data, we explore the topic of model selection for an appropriate mathematical model and corresponding statistical models, and use techniques including ANOVA-based model comparison tests and residual plot analysis to make the best selections. In addition we explore the topic of data information content: in this example, we are testing the question of whether data, as it is currently collected, can support time-dependent parameter estimation. Furthermore, we investigate the statistical assumptions often haphazardly made in the process of parameter estimation and consider the implications of unfounded assumptions.

De novo construction of an expanded transcriptome assembly for the western tarnished plant bug, Lygus hesperus.

BackgroundThe plant bug Lygus hesperus Knight is a polyphagous pest of many economically important crops. Despite its pest status, little is known about the molecular mechanisms responsible for much of the biology of this species. Earlier Lygus transcriptome assemblies were limited by low read depth, or because they focused on specific conditions. To generate a more comprehensive transcriptome, we supplemented previous datasets with new reads corresponding to specific tissues (heads, antennae, and male reproductive tissues). This transcriptome augments current Lygus molecular resources and provides the foundational knowledge critical for future comparative studies.FindingsAn expanded, Trinity-based de novo transcriptome assembly for L. hesperus was generated using previously published whole body Illumina data, supplemented with 293 million bp of new raw sequencing data corresponding to five tissue-specific cDNA libraries and 11 Illumina sequencing runs. The updated transcriptome consists of 22,022 transcripts (average length of 2075 nt), 62 % of which contain complete open reading frames. Significant coverage of the BUSCO (benchmarking universal single-copy orthologs) dataset and robust metrics indicate that the transcriptome is a quality assembly with a high degree of completeness. Initial assessment of the new assembly’s utility revealed that the length and abundance of transcripts predicted to regulate insect physiology and chemosensation have improved, compared with previous L. hesperus assemblies.ConclusionsThis transcriptome represents a significant expansion of Lygus transcriptome data, and improves foundational knowledge about the molecular mechanisms underlying L. hesperus biology. The dataset is publically available in NCBI and GigaDB as a resource for researchers.

Characterization of Lygus hesperus (Hemiptera: Miridae) Feeding and Oviposition Injury on Celery Seedlings

The western tarnished plant bug, Lygus hesperus Knight (Hemiptera: Miridae), can be a serious pest of celery, Apium graveolens dulce (Mill.) Pers. in the Central Coast region of California. Little is known about injury symptoms caused by L. hesperus adults on celery. When celery seedlings were exposed to L. hesperus adults, their crown area was found destroyed with necrotic dead tissue. Destroyed crowns of dead seedlings were observed when seedlings were exposed to five or more L. hesperus adults for ≥24 h but was not observed on seedlings exposed ≤12 h. In addition, elongated lesions were noticed on the celery petiole and were significantly greater when exposed to five or more L. hesperus adults for as little as 4 h. Number of elongated lesion injuries and number of eggs recovered from elongated lesions was correlated (r = 0.66; P < 0.001). Data provide key diagnostic symptoms of L. hesperus feeding and ovipositional injury on celery seedlings. Also, this study expands our understandings on the effects of L. hesperus adult density and duration of exposure which reinforces the need for regular scouting, and immediate management decisions and action to reduce losses from L. hesperus injury in both celery seedlings and mature plants in greenhouse and field settings, respectively Accepted for publication 27 April 2016. Published 4 May 2016.

Regulatory roles of biogenic amines and juvenile hormone in the reproductive behavior of the western tarnished plant bug (Lygus hesperus).

Mating induces behavioral and physiological changes in the plant bug Lygus hesperus Knight (Hemiptera: Miridae). After receiving seminal products, which include the systemic regulator juvenile hormone (JH), females enter a post-mating period lasting several days during which they enhance their oviposition rate and lose interest in remating. To elucidate the regulation of these behavioral changes in L. hesperus, biogenic amines were quantified in the heads of females at 5 min, 1 h and 24 h after copulation and compared to levels in virgins using high-performance liquid chromatography coupled with electrochemical detection. Mating significantly increased dopamine (DA) after 1 and 24 h, and decreased octopamine (OA) after 5 min and 1 h. Serotonin did not change with mating, but tyramine was significantly reduced after 5 min. While injection of amines into virgin females did not influence sexual receptivity, OA caused a decrease in oviposition during the 24 h following injection. Topical application of the JH analog methoprene to virgins caused an increase in DA, and a decline in mating propensity, but did not influence other amines or the oviposition rate. The results suggest the decline in OA observed immediately after mating may promote egg laying, and that male-derived JH may induce an increase in DA that could account for the post-mating loss of sexual receptivity.

Diapause Response to Photoperiod in an Arizona Population ofLygus hesperus(Hemiptera: Miridae)

Abstract The western tarnished plant bug (Lygus hesperus Knight) is an important crop pest in the western United States that overwinters in an adult diapause. However, knowledge of L. hesperus diapause is incomplete. Eggs from field-collected adults were reared under photoperiods of 10:14, 11:13, 12:12, and 13:11 (L:D) h at 26.7 ± 1°C, and the diapause response for each gender was modeled by a logistic function. Incidence of a recently reported “glass bead” fat body type also was examined. Validation studies using the same methods were subsequently conducted using photoperiods of 10.5:13.5, 11.5:12.5, and 12.5:11.5 (L:D) h. No effects of bug gender, photoperiod, or diapause status on occurrence of the novel fat type were detected. Estimates of diapause in validation studies were within confidence intervals for initial predictions, but systematic deviations from initial predictions prompted refitting of the models to include validation data. Refitted functions estimated critical photoperiods of 11h44min fo...

Temperature-Dependent Survival of Adult Lygus hesperus (Hemiptera: Miridae).

The western tarnished plant bug, Lygus hesperus Knight (Hemiptera: Miridae), is a key pest of many horticultural and agronomic crops in the western United States. Despite its well documented pest status, many aspects of the basic biology, including overwintering ecology, of L. hesperus are poorly understood. We examined the influence of eight constant temperatures from 10 to 35°C on survival of nondiapausing adult L. hesperus held with or without food, and the consequences of exposure to an extended period at 10°C on subsequent reproduction. Survival analyses indicated that, on average, fed insects tended to live longer than unfed insects, females lived longer than males, and the survival time decreased with increasing temperature. Nonlinear regressions indicated that median survival for insects grouped by gender and feeding status declined exponentially with increasing temperature. Survival functions for combinations of insect class (gender and feeding status) and temperature were adequately described by the respective two-parameter logistic functions. When adults were held for 9 d at 27°C with food after a 33-d period at 10°C either with or without food, no deleterious effects of prior starvation on propensity to mate or fecundity were demonstrated. These findings indicate that when temperatures are low, nondiapausing L. hesperus adults are capable of extended host-free survival with little or no impact on subsequent reproduction. Our findings suggest the current understanding of L. hesperus overwintering dynamics is incomplete. In addition, our results provide quantitative baseline information to facilitate more comprehensive investigation of the ecology of L. hesperus overwintering.

28S Ribosomal RNA Sequences Separate Five Prominent Lygus (Hemiptera: Miridae) Pest Species Into Three Species Clusters

ABSTRACT A segment of the nuclear 28S rRNA gene was compared among six species of Lygus [Lygus hesperus (Knight), Lygus keltoni (Schwartz), Lygus borealis (Kelton), Lygus elisus (Van Duzee), Lygus lineolaris (Palisot de Beauvois), and Lygus vanduzeei (Knight)]. The DNA sequences were separate into three main groups. The LL group contains L. lineolaris and L. vanduzeei. Group LBLE is composed of L. elisus and most of L. borealis. Group LH includes L. hesperus and most of L. keltoni. Some L. keltoni were part of the LBLE group and some L. borealis were part of the LH group. The 28S region does not contain sufficient genetic polymorphism to delineate species. The apparent polyphyly of L. borealis and L. keltoni could reflect historic interbreeding, recent development of a hybrid swarm, or highlight inadequacies of morphospecies identification.

Molecular Cloning and Characterization of G Alpha Proteins from the Western Tarnished Plant Bug, Lygus hesperus.

The Gα subunits of heterotrimeric G proteins play critical roles in the activation of diverse signal transduction cascades. However, the role of these genes in chemosensation remains to be fully elucidated. To initiate a comprehensive survey of signal transduction genes, we used homology-based cloning methods and transcriptome data mining to identity Gα subunits in the western tarnished plant bug (Lygus hesperus Knight). Among the nine sequences identified were single variants of the Gαi, Gαo, Gαs, and Gα12 subfamilies and five alternative splice variants of the Gαq subfamily. Sequence alignment and phylogenetic analyses of the putative L. hesperus Gα subunits support initial classifications and are consistent with established evolutionary relationships. End-point PCR-based profiling of the transcripts indicated head specific expression for LhGαq4, and largely ubiquitous expression, albeit at varying levels, for the other LhGα transcripts. All subfamilies were amplified from L. hesperus chemosensory tissues, suggesting potential roles in olfaction and/or gustation. Immunohistochemical staining of cultured insect cells transiently expressing recombinant His-tagged LhGαi, LhGαs, and LhGαq1 revealed plasma membrane targeting, suggesting the respective sequences encode functional G protein subunits.

Model Comparison Tests to Determine Data Information Content.

In the context of inverse or parameter estimation problems we demonstrate the use of statistically based model comparison tests in several examples of practical interest. In these examples we are interested in questions related to information content of a particular given data set and whether the data will support a more complicated model to describe it. In the first example we compare fits for several different models to describe simple decay in a size histogram for aggregates in amyloid fibril formation. In a second example we investigate whether the information content in data sets for the pest Lygus hesperus in cotton fields as it is currently collected is sufficient to support a model in which one distinguishes between nymphs and adults. Finally in a third example with data for patients having undergone an organ transplant, we question whether the data content is sufficient to estimate more than 5 of the fundamental parameters in a particular dynamic model.

Transcriptome-Based Identification of ABC Transporters in the Western Tarnished Plant Bug Lygus hesperus

ATP-binding cassette (ABC) transporters are a large superfamily of proteins that mediate diverse physiological functions by coupling ATP hydrolysis with substrate transport across lipid membranes. In insects, these proteins play roles in metabolism, development, eye pigmentation, and xenobiotic clearance. While ABC transporters have been extensively studied in vertebrates, less is known concerning this superfamily in insects, particularly hemipteran pests. We used RNA-Seq transcriptome sequencing to identify 65 putative ABC transporter sequences (including 36 full-length sequences) from the eight ABC subfamilies in the western tarnished plant bug (Lygus hesperus), a polyphagous agricultural pest. Phylogenetic analyses revealed clear orthologous relationships with ABC transporters linked to insecticide/xenobiotic clearance and indicated lineage specific expansion of the L. hesperus ABCG and ABCH subfamilies. The transcriptional profile of 13 LhABCs representative of the ABCA, ABCB, ABCC, ABCG, and ABCH subfamilies was examined across L. hesperus development and within sex-specific adult tissues. All of the transcripts were amplified from both reproductively immature and mature adults and all but LhABCA8 were expressed to some degree in eggs. Expression of LhABCA8 was spatially localized to the testis and temporally timed with male reproductive development, suggesting a potential role in sexual maturation and/or spermatozoa protection. Elevated expression of LhABCC5 in Malpighian tubules suggests a possible role in xenobiotic clearance. Our results provide the first transcriptome-wide analysis of ABC transporters in an agriculturally important hemipteran pest and, because ABC transporters are known to be important mediators of insecticidal resistance, will provide the basis for future biochemical and toxicological studies on the role of this protein family in insecticide resistance in Lygus species.

Effects of Irrigation Levels on Interactions AmongLygus hesperus(Hemiptera: Miridae), Insecticides, and Predators in Cotton

Variation in plant quality and natural enemy abundance plays an important role in insect population dynamics. In manipulative field studies, we evaluated the impact of varying irrigation levels and insecticide type on densities of Lygus hesperus Knight and the arthropod predator community in cotton. Three watering levels were established via irrigations timed according to three levels of percent soil water depletion (SWD): 20, 40, or 60, where 40% SWD is considered standard grower practice, 60% represents a deficit condition likely to impose plant productivity losses, and 20% represents surplus conditions with likely consequences on excessive vegetative plant production. The two key L. hesperus insecticides used were the broad-spectrum insecticide acephate and the selective insecticide flonicamid, along with an untreated check. We hypothesized that densities of L. hesperus and its associated predators would be elevated at higher irrigation levels and that insecticides would differentially impact L. hesperus and predator dynamics depending on their selectivity. L. hesperus were more abundant at the higher irrigation level (20% SWD) but the predator densities were unaffected by irrigation levels. Both L. hesperus and its predators were affected by the selectivity of the insecticide with highest L. hesperus densities and lowest predator abundance where the broad spectrum insecticide (acephate) was used. There were no direct interactions between irrigation level and insecticides, indicating that insecticide effects on L. hesperus and its predators were not influenced by the irrigation levels used here. The implications of these findings on the overall ecology of insect-plant dynamics and yield in cotton are discussed.

Potential Transmission of <I>Pantoea</I> spp. and <I>Serratia marcescens</I> (Enterobacteriales: Enterobacteriaceae) to Plants by <I>Lygus hesperus</I> (Hemiptera: Miridae)

Lygus hesperus Knight (Hemiptera: Miridae) is a key agricultural pest in the western United States. In a recent study, proteins from Pantoea ananatis and Serratia marcescens (Enterobacteriales: Enterobacteriaceae) were identified in diet that was stylet probed and fed on by L. hesperus adults. P. ananatis and S. marcescens are ubiquitous bacteria that infect a wide range of crops. The objective of our study was to determine whether L. hesperus transfer P. ananatis and S. marcescens to food substrates during stylet-probing activities. Sucrose (5%) was spread under parafilm and exposed to adult L. hesperus for 24 h. Diet similarly prepared but not exposed to insects was used for controls. MacConkey agar was inoculated with stylet-probed or control diets and incubated at 25 degrees C. After 24 h, bacterial colonies were observed on agar that was inoculated with stylet-probed diet, but were not observed on agar inoculated with control diet. Isolated bacterial colonies were putatively identified as either Pantoea spp. or S. marcescens using the API 20e identification kit. These results indicate that L. hesperus is capable of vectoring P. ananatis and S. marcescens.

Effect of Selected Insecticides onLygus hesperus(Heteroptera: Miridae) Oviposition Behavior in Cotton

Oviposition behavior of western tarnished plant bug, Lygus hesperus Knight, as affected by residual insecticides, was studied in potted as well as field-grown cotton. In this study, we investigated the spatial distribution and phytotomical preference of Lygus oviposition in presquaring and blooming cotton, as affected by selected insecticides. Flonicamid, acephate, and cypermethrin were applied to cotton at 82, 516, and 114 g (active ingredient)/ha, respectively. At 3 d posttreatment, a gravid female Lygus was caged on the plants. After 4 d, caged plants were harvested and eggs were counted by whole plant dissection. Results indicated significantly greater egg deposition in untreated controls than treated plants in both potted and field-grown cotton. For untreated plants, Lygus preferred to oviposit on the pulvinus and leaf petiole, where 76 and 85% of eggs were laid in potted and field-grown cotton, respectively. For insecticide-treated plants, no plant structure preference was observed, although fewer eggs were laid. The upper stratum of the plant canopy had significantly more eggs than the lower or middle strata of untreated plants, while more eggs were observed in the middle strata of plants treated with acephate in field-grown cotton. Sublethal effects could not be adequately assessed in the cypermethrin treatment owing to high Lygus mortality.

Identification and characterization of a sex peptide receptor‐like transcript from the western tarnished plant bug Lygus hesperus

Lygus hesperus females exhibit a post-mating behavioural switch that triggers increased egg laying and decreased sexual interest. In Drosophila melanogaster, these changes are controlled by sex peptide (SP) and the sex peptide receptor (DmSPR). In Helicoverpa armigera, SPR (HaSPR) also regulates some post-mating behaviour; however, myoinhibiting peptides (MIPs) have been identified as the SPR ancestral ligand, indicating that SPR is a pleiotropic receptor. In the present study, we identified a transcript, designated L. hesperus SPR (LhSPR), that is homologous to known SPRs and which is expressed throughout development and in most adult tissues. LhSPR was most abundant in female seminal depositories and heads as well as the hindgut/midgut of both sexes. In vitro analyses revealed that fluorescent chimeras of LhSPR, DmSPR and HaSPR localized to the cell surface of cultured insect cells, but only DmSPR and HaSPR bound carboxytetramethylrhodamine-labelled analogues of DmSP21-36 and DmMIP4. Injected DmSP21-36 also failed to have an effect on L. hesperus mating receptivity. Potential divergence in the LhSPR binding pocket may be linked to receptor-ligand co-evolution as 9 of 13 MIPs encoded by a putative L. hesperus MIP precursor exhibit an atypical W-X7 -Wamide motif vs the W-X6 -Wamide and W-X8 -Wamide motifs of Drosophila MIPs and SP.

Ecoinformatics reveals effects of crop rotational histories on cotton yield.

Crop rotation has been practiced for centuries in an effort to improve agricultural yield. However, the directions, magnitudes, and mechanisms of the yield effects of various crop rotations remain poorly understood in many systems. In order to better understand how crop rotation influences cotton yield, we used hierarchical Bayesian models to analyze a large ecoinformatics database consisting of records of commercial cotton crops grown in California's San Joaquin Valley. We identified several crops that, when grown in a field the year before a cotton crop, were associated with increased or decreased cotton yield. Furthermore, there was a negative association between the effect of the prior year's crop on June densities of the pest Lygus hesperus and the effect of the prior year's crop on cotton yield. This suggested that some crops may enhance L. hesperus densities in the surrounding agricultural landscape, because residual L. hesperus populations from the previous year cannot continuously inhabit a focal field and attack a subsequent cotton crop. In addition, we found that cotton yield declined approximately 2.4% for each additional year in which cotton was grown consecutively in a field prior to the focal cotton crop. Because L. hesperus is quite mobile, the effects of crop rotation on L. hesperus would likely not be revealed by small plot experimentation. These results provide an example of how ecoinformatics datasets, which capture the true spatial scale of commercial agriculture, can be used to enhance agricultural productivity.

Molecular and functional characterization of multiple aquaporin water channel proteins from the western tarnished plant bug, Lygus hesperus

Aquaporins (AQPs) are integral membrane channel proteins that facilitate the bidirectional transfer of water or other small solutes across biological membranes involved in numerous essential physiological processes. In arthropods, AQPs belong to several subfamilies, which contribute to osmoregulation, respiration, cryoprotection, anhydrobiosis, and excretion. We cloned and characterized five novel AQPs from the western tarnished plant bug, Lygus hesperus, a polyphagous insect pest of food and fiber crops throughout western North America. The L. hesperus AQPs (LhAQP1-5) belong to different phylogenetic subfamilies, have unique transcription profiles and cellular localizations, and all transport water (but not glycerol) when heterologously expressed in Xenopus laevis oocytes. Our results demonstrate that multiple AQPs with possible compensatory functions are produced in L. hesperus that likely play important roles in maintaining water homeostasis in this important insect pest.

Characterization of male-derived factors inhibiting female sexual receptivity in Lygus hesperus

Newly mated females of the plant bug, Lygus hesperus Knight, enter a refractory period during which their sexual receptivity to courting males is greatly reduced for several days. This behavioral change appears to be induced by male-derived factors delivered in the spermatophore during copulation. To better understand the source of the factor(s) responsible for the inhibition, the homogenates of spermatophores, or of the individual organs that provide the constituents of the spermatophore, were injected directly into the abdomen of virgin females. The contents of the lateral and medial accessory glands both appear to produce inhibitory effects, but those of the seminal vesicle had no effect. Treatment of the homogenate also indicated that the active factor(s) is heat labile and water soluble. Several unique proteins were found in the water soluble fraction of the spermatophore, one of which is similar in size to the Drosophila melanogaster sex peptide, a male derived compound known to inhibit receptivity in female flies. In addition, spermatophores contained a substantial quantity of juvenile hormone, a key endocrine regulator of reproductive behavior and physiology in most insects. The results support the hypothesized role of males in manipulating the post-mating behavior of females, and suggest this is achieved through multiple components that act in concert to induce both short- and long-term effects.

Ecoinformatics Can Reveal Yield Gaps Associated with Crop-Pest Interactions: A Proof-of-Concept

Farmers and private consultants execute a vast, decentralized data collection effort with each cropping cycle, as they gather pest density data to make real-time pest management decisions. Here we present a proof of concept for an ecoinformatics approach to pest management research, which attempts to harness these data to answer questions about pest-crop interactions. The impact of herbivory by Lygus hesperus on cotton is explored as a case study. Consultant-derived data satisfied a ‘positive control’ test for data quality by clearly resolving the expected negative relationship between L. hesperus density and retention of flower buds. The enhanced statistical power afforded by the large ecoinformatics dataset revealed an early-season window of crop sensitivity, during which L. hesperus densities as low as 1-2 per sample were associated with yield loss. In contrast, during the mid-season insecticide use by farmers was often unnecessary, as cotton compensated fully for moderate L. hesperus densities. Because the dataset emerged from the commercial production setting, it also revealed the limited degree to which farmers were willing to delay crop harvest to provide opportunities for compensatory fruiting. Observational approaches to pest management research have strengths and weaknesses that complement those of traditional, experimental approaches; combining these methods can contribute to enhanced agricultural productivity.