Host plant preference of Lygus hesperus (Hemiptera: Miridae) in 4 field crops: potato, alfalfa, carrot, and pea.

The western tarnished plant bug, Lygus hesperus (Knight), has emerged as a pest of potatoes (Solanum tuberosum L.) in the Lower Columbia Basin of Oregon and Washington. This species is generally found infesting several other field-grown crops in the region; however, their host preference is poorly understood. Thus, greenhouse cage experiments were conducted to evaluate L. hesperus host preference by simultaneously presenting adults with 4 host plants: potato, alfalfa, Medicago sativa L., carrot, Daucus carota L., and pea, Pisum sativum L. In addition, an oviposition test was conducted. The results indicated that L. hesperus actively chose as a host and as an oviposition substrate among the 4 host plants. We found a significantly higher number of adults on alfalfa and potato plants over carrot or pea plants at 6 h, 24 h, and 48 h after adults were released into the cage. However, 96 h after release, more L. hesperus were found in alfalfa. In addition, female L. hesperus strongly preferred potato and alfalfa plants as an oviposition substrate over carrot and pea plants at 96 h after release.

Developing lygus bug control strategies in potatoes: plant variety, vertical distribution effect, and insecticide efficacy studies.

The Columbia Basin of Oregon and Washington is one of the most productive potatoes, Solanum tuberosum L., growing regions in the United States affected by numerous insect pests. Lygus bugs, Lygus spp. (Hemiptera: Miridae), are an increasing problem in potatoes. In 2015, after an outbreak of lygus bugs in potatoes in the Columbia Basin, potato producers used multiple applications of insecticides to control lygus bugs. However, it is poorly researched whether lygus bugs can cause economic damage to the crop. Therefore, our objectives were (i) to determine lygus bugs presence in potato plants, (ii) to determine damage on most commonly grown potato varieties (e.g., Alturas Russet, Ranger Russet, Umatilla Russet, Russet Burbank, and Clearwater Russet), (iii) to determine the number of insecticide applications needed to control lygus bugs, and (iv) to estimate the relationship between lygus bug density and potato yield loss. This study demonstrated that the lygus complex is widely present in the Columbia Basin, Lygus spp. prefers the upper 1/3 section of potato plants in all varieties tested, and the number of applications throughout a field season does not affect yield regardless of variety.

Alfalfa weevils (Coleoptera: Curculionidae) in the western United States are resistant to multiple type II pyrethroid insecticides.

The alfalfa weevil (Hypera postica Gyllenhal (Coleoptera: Curculionidae)), a key pest of alfalfa (Medicago sativa L. (Fabales: Fabacae)) across the US, has developed resistance to pyrethroids lambda-cyhalothrin and zeta-cypermethrin in at least 6 western US states. Unfortunately, 6 pyrethroid active ingredients represent most commercial insecticides registered for alfalfa weevil control in forage alfalfa systems. Thus, the loss of efficacy of this mode of action group due to multiple resistance represents a significant agricultural challenge because of a limited registered alternative mode of actions. To evaluate the extent and severity of resistance among pyrethroids around the United States, laboratory bioassays using larvae from Arizona, California, Montana, Oregon, Washington, and Wyoming, including both the Egyptian and western strains, were conducted. Results indicated that similar degrees of resistance among type II pyrethroids as determined by both laboratory bioassays and field trials exist. The LC50 values of alpha-cypermethrin, beta-cyfluthrin and zeta-cypermethrin produced significant correlations with the LC50 values of lambda-cyhalothrin. In contrast, resistance did not include type I pyrethroid, bifenthrin (registered for seed alfalfa production), whose LC50 values yielded a slope not significantly different from zero when correlated with lambda-cyhalothrin. Field trials conducted in Arizona, Montana, and Washington corroborated laboratory results, as commercial formulations with type II pyrethroid active ingredients failed to adequately control alfalfa weevils resistant to lambda-cyhalothrin. Integrated resistance management recommendations are discussed.

Chromosomal-level genome assembly of potato tuberworm, Phthorimaea operculella: a pest of solanaceous crops.

The potato tuberworm, Phthorimaea operculella Zeller, is an oligophagous pest feeding on crops mainly belonging to the family Solanaceae. It is one of the most destructive pests of potato worldwide and attacks foliage and tubers in the field and in storage. However, the lack of a high-quality reference genome has hindered the association of phenotypic traits with their genetic basis. Here, we report on the genome assembly of P. operculella at the chromosomal level. Using Illumina, Nanopore and Hi-C sequencing, a 648.2 Mb genome was generated from 665 contigs, with an N50 length of 3.2 Mb, and 92.0% (596/648.2 Mb) of the assembly was anchored to 29 chromosomes. In total, 16619 genes were annotated, and 92.4% of BUSCO genes were fully represented. The chromosome-level genome of P. operculella will provide a significant resource for understanding the genetic basis for the biological study of this insect, and for promoting the integrative management of this pest in future.

Pest population dynamics are related to a continental overwintering gradient.

Overwintering success is an important determinant of arthropod populations that must be considered as climate change continues to influence the spatiotemporal population dynamics of agricultural pests. Using a long-term monitoring database and biologically relevant overwintering zones, we modeled the annual and seasonal population dynamics of a common pest, Helicoverpa zea (Boddie), based on three overwintering suitability zones throughout North America using four decades of soil temperatures: the southern range (able to persist through winter), transitional zone (uncertain overwintering survivorship), and northern limits (unable to survive winter). Our model indicates H. zea population dynamics are hierarchically structured with continental-level effects that are partitioned into three geographic zones. Seasonal populations were initially detected in the southern range, where they experienced multiple large population peaks. All three zones experienced a final peak between late July (southern range) and mid-August to mid-September (transitional zone and northern limits). The southern range expanded by 3% since 1981 and is projected to increase by twofold by 2099 but the areas of other zones are expected to decrease in the future. These changes suggest larger populations may persist at higher latitudes in the future due to reduced low-temperature lethal events during winter. Because H. zea is a highly migratory pest, predicting when populations accumulate in one region can inform synchronous or lagged population development in other regions. We show the value of combining long-term datasets, remotely sensed data, and laboratory findings to inform forecasting of insect pests.

Flight Potential of Western Tarnished Plant Bug (Hemiptera: Miridae).

The western tarnished plant bug, Lygus hesperus Knight, is an economically important pest of several agricultural crops in the western United States. It is an increasing threat to potato, Solanum tuberosum L. (Solanales: Solanaceae), in the diverse landscape of the Columbia Basin of Oregon and Washington. In this study, flight mills were used to investigate the flight capacity of L. hesperus with the aim of better understand its dispersive characteristics in the agricultural landscape. Explicitly, we investigated the effects of biological factors such as generation, gender, and body weight on the flight potential of adult L. hesperus adults collected from field populations during spring and summer of 2019 and 2020. The study flight parameters assessed were distance, activity, velocity, and diel periodicity. In 24-h flight mill assays, a clear dichotomy pattern was found in sum flown distance for adults that travelled 1 km or shorter and adults that travelled greater than 1 km. Individuals from the summer population flew farther and more actively than those from the overwintered population. Female L. hesperus flew farther and were more active compared to males. Adult body weight before the flight was directly proportional to flight distance and number of flights, but not with velocity. Overwintered L. hesperus adults lost a higher percentage of their pre-flight body weight compared to summer adults over the course of the study. To the best of our knowledge, this is the first study that demonstrated that L. hesperus summer adult population has the flight ability to disperse greater distance in the agricultural landscape than overwintered population.

Predicting Phenology of Four Major Hemipteran Pests to Enhance Integrated Pest Management Programs in Potatoes in the Lower Columbia Basin.

The potato crop (Solanum tuberosum L.) is affected by various hemipteran insect pests including Circulifer tenellus Baker, Lygus spp., Myzus persicae Sulzer, and Macrosiphum euphorbiae Thomas. These pests can cause direct foliage damage or vector plant pathogens, and consequently reduce potato yield. Gaining insights into which factors have the greatest impact on seasonal population growth of insect pests is key for improving integrated pest management strategies. Moreover, abiotic and biotic cues such as temperature and crop growth stage can strongly influence insect population growth. Hence, the seasonal population dynamics of C. tenellus, Lygus spp., M. persicae, and M. euphorbiae, and temperature, were monitored weekly throughout potato growing seasons in commercial fields located in the lower Columbia Basin (USA). Using a multi-year dataset, we developed phenology models of each pest based on the accumulated degree days (DD) and potato days (PD). Temperature-mediated population growth models suggest that C. tenellus and Lygus spp. are the first of the pests to colonize the potato crop fields, with 90% of cumulative catch by 2,823 and 1,776 DD, respectively. In contrast, M. persicae and M. euphorbiae populations increased more gradually over the course of the season, with 90% cumulative catch by 5,590 and 5,047 DD, respectively. PD-mediated population growth models suggest that 50% of the populations of C. tenellus, Lygus spp., and M. persicae can be collected at potato tuber growth stage, while 50% of the M. euphorbiae population at tuber initiation stage. The results presented here will help in improving hemipteran potato pests' management.

Baseline Susceptibility of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) to Commonly Used Insecticides in the Columbia Basin.

Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), is one of the most challenging pests of potato, Solanum tuberosum L., largely due to its propensity to develop insecticide resistance. Historically, L. decemlineata has rapidly evolved resistance to all major classes of synthetic insecticides, particularly in the eastern United States. However, in the U.S. Pacific Northwest, there have thus far been no confirmed reports of insecticide resistance despite anecdotal accounts of control failure. Hence, the objective of this study was to develop baseline data on the susceptibility of L. decemlineata in the Columbia Basin to abamectin, imidacloprid, and spinetoram, three insecticides commonly used to manage this insect. In 2018 and 2019, baseline susceptibility of four L. decemlineata populations, three from the Columbia Basin and one from Wisconsin (used as a resistant reference), was examined using topical LD50 bioassays. In general, L. decemlineata populations in the Columbia Basin exhibited relatively high sensitivity to imidacloprid, but variable sensitivity to abamectin and spinetoram among sites and years. Although small sample sizes hindered estimation of statistically significant LD50 values, results suggest that L. decemlineata in the Columbia Basin are beginning to develop levels of insensitivity to spinetoram, and possibly abamectin that are comparable to insecticide-resistant populations in Wisconsin. This preliminary examination of geographic variation in sensitivity to commonly used insecticides reinforces the value of rotating insecticide modes of action and suggests the need for continued monitoring for the development of insecticide resistance throughout the U.S. Pacific Northwest.

Selection for high levels of resistance to double-stranded RNA (dsRNA) in Colorado potato beetle (Leptinotarsa decemlineata Say) using non-transgenic foliar delivery.

Insecticidal double-stranded RNAs (dsRNAs) silence expression of vital genes by activating the RNA interference (RNAi) mechanism in insect cells. Despite high commercial interest in insecticidal dsRNA, information on resistance to dsRNA is scarce, particularly for dsRNA products with non-transgenic delivery (ex. foliar/topical application) nearing regulatory review. We report the development of the CEAS 300 population of Colorado potato beetle (Leptinotarsa decemlineata Say) (Coleoptera: Chrysomelidae) with > 11,100-fold resistance to a dsRNA targeting the V-ATPase subunit A gene after nine episodes of selection using non-transgenic delivery by foliar coating. Resistance was associated with lack of target gene down-regulation in CEAS 300 larvae and cross-resistance to another dsRNA target (COPI ß; Coatomer subunit beta). In contrast, CEAS 300 larvae showed very low (~ 4-fold) reduced susceptibility to the Cry3Aa insecticidal protein from Bacillus thuringiensis. Resistance to dsRNA in CEAS 300 is transmitted as an autosomal recessive trait and is polygenic. These data represent the first documented case of resistance in an insect pest with high pesticide resistance potential using dsRNA delivered through non-transgenic techniques. Information on the genetics of resistance and availability of dsRNA-resistant L. decemlineata guide the design of resistance management tools and allow research to identify resistance alleles and estimate resistance risks.

Vertical Distribution of Insect Pests Using Insect Towers Placed Near Potato Fields in the Lower Columbia Basin.

This study was conducted at the Oregon State University Hermiston Agricultural Research and Extension Center, Hermiston, Umatilla County, OR, during the 2016 and 2017 potato, Solanum tuberosum L. (Solanales: Solanaceae), growing seasons. The objective was to determine the vertical distribution of hemipteran (Bactericera cockerelli Sulc, Circulifer tenellus Baker, Myzus persicae Sulzer, Macrosiphum euphorbiae Thomas, and Lygus spp.) and thysanopteran (Frankliniella occidentalis Pergande and Thrips tabaci Lindeman) potato pests using insect towers placed near potato fields. Towers were 8 m tall and secured to the ground with metal cables. In each tower, yellow sticky cards were mounted at 1.5 m intervals up to 7.6 m aboveground. Data were collected at 7-d intervals from mid-April until mid or end of August. This study showed that B. cockerelli, C. tenellus, M. persicae, Lygus spp., and both species of thrips were captured on sticky cards placed closest to the ground; in both years, as sticky card height increased, abundances decreased. In contrast, trapped M. euphorbiae numbers were not affected by sticky card height. To our knowledge, this is the first study in the lower Columbia Basin of Oregon that evaluated the vertical distribution of major potato pests.

Host plants and Wolbachia shape the population genetics of sympatric herbivore populations.

Changing climate and land-use practices have the potential to bring previously isolated populations of pest insects into new sympatry. This heightens the need to better understand how differing patterns of host-plant association, and unique endosymbionts, serve to promote genetic isolation or integration. We addressed these factors in populations of potato psyllid, Bactericera cockerelli (Sulc), a generalist herbivore that vectors a bacterial pathogen (Candidatus Liberibacter solanacearum, causal pathogen of zebra chip disease) of potato (Solanum tuberosum L.). Genome-wide SNP data revealed two major genetic clusters-psyllids collected from potato crops were genetically similar to psyllids found on a common weed, Lycium spp., but dissimilar from those found on another common non-crop host, Solanum dulcamara L. Most psyllids found on Lycium spp. and potato represented a single mitochondrial cytochrome oxidase I (COI) haplotype that has been suggested to not be native to the region, and whose arrival may have been concurrent with zebra chip disease first emerging. The putatively introduced COI haplotype usually co-occurred with endosymbiotic Wolbachia, while the putatively resident COI haplotype generally did not. Genetic intermediates between the two genetic populations of insects were rare, consistent with recent sympatry or reproductive isolation, although admixture patterns of apparent hybrids were consistent with introgression of genes from introduced into resident populations. Our results suggest that both host-plant associations and endosymbionts are shaping the population genetic structure of sympatric psyllid populations associated with different non-crop hosts. It is of future interest to explicitly examine vectorial capacity of the two populations and their potential hybrids, as population structure and hybridization might alter regional vector capacity and disease outbreaks.

Wireworm (Coleoptera: Elateridae) genomic analysis reveals putative cryptic species, population structure, and adaptation to pest control.

The larvae of click beetles (Coleoptera: Elateridae), known as "wireworms," are agricultural pests that pose a substantial economic threat worldwide. We produced one of the first wireworm genome assemblies (Limonius californicus), and investigated population structure and phylogenetic relationships of three species (L. californicus, L. infuscatus, L. canus) across the northwest US and southwest Canada using genome-wide markers (RADseq) and genome skimming. We found two species (L. californicus and L. infuscatus) are comprised of multiple genetically distinct groups that diverged in the Pleistocene but have no known distinguishing morphological characters, and therefore could be considered cryptic species complexes. We also found within-species population structure across relatively short geographic distances. Genome scans for selection provided preliminary evidence for signatures of adaptation associated with different pesticide treatments in an agricultural field trial for L. canus. We demonstrate that genomic tools can be a strong asset in developing effective wireworm control strategies.

Seasonal Population Dynamics of Potato Psyllid (Hemiptera: Triozidae) in the Columbia River Basin.

Understanding factors that affect the population dynamics of insect pest species is key for developing integrated pest management strategies in agroecosystems. Most insect pest populations are strongly regulated by abiotic factors such as temperature and precipitation, and assessing relationships between abiotic conditions and pest dynamics can aid decision-making. However, many pests are also managed with insecticides, which can confound relationships between abiotic factors and pest dynamics. Here we used data from a regional monitoring network in the Pacific Northwest United States to explore effects of abiotic factors on populations of an intensively managed potato pest, the potato psyllid (Bactericera cockerelli Sulc), which can vector Candidatus Liberibacter psyllaurus, a bacterial pathogen of potatoes. We assessed effects of temperature on psyllid populations, and show psyllid population growth followed predictable patterns within each year, but there was considerable variation across years in psyllid abundance. Examination of seasonal weather patterns suggested that in 2017, when psyllid populations were less abundant by several orders of magnitude than other years, a particularly long and cold period of winter weather may have harmed overwintering populations and limited population growth. The rate of degree-day accumulation over time, as well as total degree-day accumulation also affected trap catch abundance, likely by mediating the number of psyllid generations per season. Our findings indicate that growers can reliably infer the potential magnitude of risk from potato psyllids using monitoring data, date of first detection, seasonal weather patterns, and population size early in the growing season.

Landscape structure and climate drive population dynamics of an insect vector within intensely managed agroecosystems.

Characterizing factors affecting insect pest populations across variable landscapes is a major challenge for agriculture. In natural ecosystems, insect populations are strongly mediated by landscape and climatic factors. However, it has proven difficult to evaluate if similar factors predict pest dynamics in agroecosystems because control tactics exert strong confounding effects. We addressed this by assessing whether species distribution models could effectively characterize dynamics of an insect pest in intensely managed agroecosystems. Our study used a regional multi-year data set to assess landscape and climatic drivers of potato psyllid (Bactericera cockerelli) populations, which are often subjected to calendar-based insecticide treatments because they transmit pathogens to crops. Despite this, we show that psyllid populations were strongly affected by landscape and climatic factors. Psyllids were more abundant in landscapes with high connectivity, low crop diversity, and large natural areas. Psyllid population dynamics were also mediated by climatic factors, particularly precipitation and humidity. Our results show that many of the same factors that drive insect population dynamics in natural ecosystems can have similar effects in an intensive agroecosystem. More broadly, our study shows that models incorporating landscape and climatic factors can describe pest populations in agroecosystems and may thus promote more sustainable pest management.

Effects of contemporary agricultural land cover on Colorado potato beetle genetic differentiation in the Columbia Basin and Central Sands.

Landscape structure, which can be manipulated in agricultural landscapes through crop rotation and modification of field edge habitats, can have important effects on connectivity among local populations of insects. Though crop rotation is known to influence the abundance of Colorado potato beetle (CPB; Leptinotarsa decemlineata Say) in potato (Solanum tuberosum L.) fields each year, whether crop rotation and intervening edge habitat also affect genetic variation among populations is unknown. We investigated the role of landscape configuration and composition in shaping patterns of genetic variation in CPB populations in the Columbia Basin of Oregon and Washington, and the Central Sands of Wisconsin, USA. We compared landscape structure and its potential suitability for dispersal, tested for effects of specific land cover types on genetic differentiation among CPB populations, and examined the relationship between crop rotation distances and genetic diversity. We found higher genetic differentiation between populations separated by low potato land cover, and lower genetic diversity in populations occupying areas with greater crop rotation distances. Importantly, these relationships were only observed in the Columbia Basin, and no other land cover types influenced CPB genetic variation. The lack of signal in Wisconsin may arise as a consequence of greater effective population size and less pronounced genetic drift. Our results suggest that the degree to which host plant land cover connectivity affects CPB genetic variation depends on population size and that power to detect landscape effects on genetic differentiation might be reduced in agricultural insect pest systems.

Patterns of genetic differentiation in Colorado potato beetle correlate with contemporary, not historic, potato land cover.

Changing landscape heterogeneity can influence connectivity and alter genetic variation in local populations, but there can be a lag between ecological change and evolutionary responses. Temporal lag effects might be acute in agroecosystems, where land cover has changed substantially in the last two centuries. Here, we evaluate how patterns of an insect pest's genetic differentiation are related to past and present agricultural land cover change over a 150-year period. We quantified change in the amount of potato, Solanum tuberosum L., land cover since 1850 using county-level agricultural census reports, obtained allele frequency data from 7,408 single-nucleotide polymorphism loci, and compared effects of historic and contemporary landscape connectivity on genetic differentiation of Colorado potato beetle, Leptinotarsa decemlineata Say, in two agricultural landscapes in the United States. We found that potato land cover peaked in Wisconsin in the early 1900s, followed by rapid decline and spatial concentration, whereas it increased in amount and extent in the Columbia Basin of Oregon and Washington beginning in the 1960s. In both landscapes, we found small effect sizes of landscape resistance on genetic differentiation, but a 20× to 1,000× larger effect of contemporary relative to historic landscape resistances. Demographic analyses suggest population size trajectories were largely consistent among regions and therefore are not likely to have differentially impacted the observed patterns of population structure in each region. Weak landscape genetic associations might instead be related to the coarse resolution of our historical land cover data. Despite rapid changes in agricultural landscapes over the last two centuries, genetic differentiation among L. decemlineata populations appears to reflect ongoing landscape change. The historical landscape genetic framework employed in this study is broadly applicable to other agricultural pests and might reveal general responses of pests to agricultural land-use change.

Molecular and Morphological Identifications Reveal Species Composition of Lygus (Hemiptera: Miridae) Bugs in Potatoes Fields in the Lower Columbia Basin of the United States.

Lygus bugs are highly polyphagous insect pests. In recent years, Lygus bugs have become more conspicuous on potato, Solanum tuberosum L., fields in the Pacific Northwest, particularly in the Lower Columbia Basin. There are concerns that direct feeding damage or potential pathogen transmission can reduce yield. Lygus species on potatoes in the region are collectively identified as 'Lygus bugs'. Overlapping physical traits and the fact that the same species exhibit morphological variations across a geographic range makes it difficult to identify Lygus to species level. Thus, in this study we used DNA barcodes in combination with morphological characters to identify Lygus species on potatoes. Three species were identified in the Lower Columbia Basin: Lygus hesperus (Knight) and Lygus elisus L. were the most common, whereas Lygus keltoni L. was the least common. Interspecific genetic distances among Lygus species were relatively low, ranging from 0.013 to 0.004. Neighbor-joining (NJ) tree clustered L. hesperus and L. elisus into two major clades, with L. keltoni forming a subclade within L. hesperus clade. Statistical parsimony analysis corroborated findings from phylogenetic analysis with L. keltoni and L. hesperus sharing one haplotype. Our study demonstrates the utility of integrating morphology and molecular markers in identifying morphologically similar species such as Lygus bugs. The study also serves as a fundamental step in contributing to developing suitable management strategies against Lygus bugs on potato.

Effect of Potato virus Y Presence in Solanum tuberosum (Solanales: Solanaceae) and Chenopodium album on Aphid (Hemiptera: Aphididae) Behavior.

This study establishes the effect of Potato Virus Y (PVY; Potyvirus) in potatoes, Solanum tuberosum L. (Solanales: Solanaceae) and in common-lambs' quarter Chenopodium album L. (Amaranthaceae) on Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and Myzus persicae Sulzer (Hemiptera: Aphididae) behavior, host preference, transmission, and fitness under field and laboratory studies. In the field, several weeds, besides C. album, were collected, including: Sisymbrium altissimum L. (Brassicaceae), Erodium cicutarium L., Lactuca serriola L., Solanum sarrachoides Sendtner (Solanaceae), and S. dulcamara L. (Solanaceae). All weeds were serologically tested for the presence of PVY. From all weeds collected, 2.3 and 34% of C. album and S. sarrachoides, respectively, were PVY-positive. From those positive samples, 72% of the PVY found were PVYN; the remaining 28% was PVYO. In addition, several aphid species were collected from those weeds: Ovatus crataegarious Walker, Macrosiphum euphorbiae (Hemiptera: Aphididae), Hyalopterus pruni Geoffroy (Hemiptera: Aphididae), Rophalosiphum madis Fitch, and 'others aphid' species were collected. The highest number of aphids were collected in E. cicutarium, followed by S. dulcamara, L. serriola, S. altissimum, and C. album. In laboratory studies, PVY-infected C. album does not induce the production of aphids. Moreover, M. persicae did not appear to have a strong preference for either healthy or PVY-infected potato plant, but they did develop a preference for infected plants after prolonged feeding. M. persicae and M. euphorbiae transmitted PVY from C. album to S. tuberosum, 44 and 37.5 % of the time. Future research should seek to identify not only other sources and prevalence of PVY in the field but vector relationships. In insect-pathogen complex continues to persist in solanaceous field crops around the world.

Effect of Planting Depth and Irrigation Regimes on Potato Tuberworm (Lepidoptera: Gelechiidae) Damage Under Central Pivot Irrigation in the Lower Columbia Basin.

Phthorimaea operculella Zeller has proven to be a limitation to potato production. Although pesticides can effectively reduce P. operculella populations, information regarding effective cultural controls is lacking. The following study was designed to evaluate the effect of different irrigation regimes and planting depths to reduce P. operculella damage under central pivot irrigation. Field trials were conducted in 2007 and 2008 and experimental plots followed standard growers' agronomic practices. Three levels of irrigation were used: optimal, 10% less than optimal, and 10% above optimal; potato planting depth was arranged as shallow, normal, and deep; normal planting was considered tubers planted at 0.15 m depth. Mines and number of larvae per plant were counted weekly until harvest and tuber damage, above and below ground, was estimated. Overall, irrigation had a stronger effect than planting depth but there were not a clear planting depth:irrigation interaction. Both years, sampling dates had a strong effect on the number of mines per plant where the number of mines per plant increased as season progressed. There were not clear trends related to mines per plant, mines per tuber or yield related to planting depth, but there were strong tendencies related to irrigation. The data presented herein provide valuable information regarding the potential to adjust irrigation to warrant better P. operculella control.

Spatial and Temporal Dynamics of Aphids (Hemiptera: Aphididae) in the Columbia Basin and Northeastern Oregon.

Aphid species, such as the potato aphid, Macrosiphum euphorbiae Thomas, and the green peach aphid, Myzus persicae Sulzer, are routinely considered the most important pests of potatoes. Potato aphid, green peach aphid, and more recently, other aphids such as the bird cherry-oat aphid Rhopalosiphum padi L. have been identified as vectors of multiple plant pathogenic viruses in potatoes. Since 2006, an area-wide trapping network consisting of ∼60 sites was developed through collaboration between researchers, extension faculty, and stakeholders, to monitor aphid populations in the Columbia Basin of Oregon (Umatilla and Morrow counties) and in northeastern Oregon (Union and Baker counties). Over a 9-yr period (2006 to 2014), aphid specimens were collected weekly using yellow bucket traps and specimens were then identified and counted to determine population levels during the growing season (May-September). Thus, aphid population data were compiled and subjected to spatial and temporal distribution analysis. Weather data, obtained from an established network of weather stations located in the monitoring areas, were used in a nonparametric multiplicative regression analysis to determine which abiotic variables may impact aphid populations. Weather conditions were characterized using confidence intervals (CIs) established based on weather data from 1999 to 2005 for each environmental variable. Aphid populations were found to have a heterogeneous distribution in most years; a few sites had high aphid populations while low numbers were observed at most sites; aphids were also found to correlate with several abiotic variables, namely, elevation, previous season temperature, and previous season dew point.