Spatial Analysis By Distance Indices Research Articles

Spatial Distribution Analysis of Invasive Pheretimoid Earthworms in West Liberty University’s Campus Woods.

The United States is currently amidst a wave of invasion by East Asian pheretimoid earthworms. Multiple genera, genus Amynthas in particular, are widespread invaders with powerful ecosystem engineering capabilities and an expanding range. Invasive populations can reach extreme densities and fluctuate heavily on weekly-to-yearly timeframes compared to other earthworms. Despite their impacts, pheretimoid genera are poorly understood, under-researched, and uncontrolled. A deeper understanding of population dynamics and their mechanisms may allow effective management practices to be developed. The research was conducted in the summer of 2023 in a forest stand at West Liberty University, a known invaded site. Spatial Analysis by Distance Indices (SADIE) was used to analyze weekly distributions of pheretimoids, showing aggregated distributions in 5 of 7 weeks of surveying, 2 of which were statistically significant (P value < 0.05). Linear regression showed no recorded environmental variables were statistically significant (P value < 0.05) in more than 1 out of 7 weeks and were inconsistent in their impact. Population density was reduced during this survey compared to previous years, likely weakening significance due to sample size. Distributions still showed aggregation, suggesting clustering behavior is the norm for pheretimoid worms even at low population sizes. As regression couldn’t adequately explain clustering patterns, more environmental variables and new data analysis techniques may be needed for future work to determine the underlying mechanisms for pheretimoids.

Spatial Patterns of Frangula alnus (Rosales: Rhamnaceae): Implications for Invasive Plant Management.

Glossy buckthorn (Frangula alnus) (Rosales: Rhamnaceae) is an invasive shrub from Europe that has been invading North America for over a century and threatening native vegetation in open and disturbed habitats. The treatment of F. alnus is currently restricted to the roadside, suggesting any individual F. alnus residing within the forest would be left unmanaged and would continue to spread in the area. This research was conducted to determine the spatial patterns and relationship of F. alnus with forest roads. The presence and density of F. alnus at 1412 sample points were recorded on four sites in the Allegheny National Forest, Pennsylvania, USA. Buffer analyses were conducted along roads to determine the relationship between F. alnus density and proximity to forest roads. Geostatistics and spatial analysis by distance indices (SADIE) were used to characterize the spatial pattern of F. alnus. Results of this study showed that F. alnus was spatially aggregated and resided beyond forest roads. Both the density and presence of F. alnus decreased as the distance from the forest road increased. These results imply the potential for precision management of F. alnus by locating and managing only where F. alnus presents.

Evaluating dispersal ability of Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae) using natural abundance technique and geostatistics

Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae), is one of the most serious insect pest worldwide. This research was done to evaluate the dispersal ability of Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae), as one of the larval parasitoids of this pest. The first trial was conducted at three plots consisting of 220 trees in each plot, which separating from each other by at least 100 m, and 13C-enriched V. canescens were released on a single tree at the center of each plot. The traps containing 50 larvae of E. kuehniella was attached at 6, 12, 18, and 24 m intervals in four directions of north, south, west, and east of the release tree. In the second trial, V. canescens were released from a tree where it located in central of each plot (n = 3, each plot = 0.3 ca). geostatistical tools and spatial analysis by distance indices (SADIE) was used to determine distribution of parasitoids in radii of 12, 24, 36 and 48m. Finally, semivariance analysis and isotope ratio indicated that the parasitoids had the highest density in 12 and 24 m radiuses after release while the spatial distribution in higher radii changed toward random or regular patterns. This result revealed that V. canescens could be a potential candidate for biological control of carob moth in pomegranate orchard and it would be attractive to develop the release points to 48 m from each other. Such information would be improved precision or site-specifc applications in agroecosystems and can also be used in site-specific pest management programs.

Within-field spatial patterns of Euschistus servus and Nezara viridula (Hemiptera: Pentatomidae) in field corn.

A complex of stink bugs, primarily the brown stink bug, Euschistus servus (Say) (Hemiptera: Pentatomidae) , and the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae) , are the most damaging insect pests of field corn, Zea mays L., in the southeastern United States. Characterizing the spatial patterns of these highly mobile, polyphagous pests is critical for developing efficient and effective sampling plans. In 2021 and 2022, stink bugs and their injury were assessed biweekly from emergence through R2 in 20 corn fields. The spatial analysis by distance indices (SADIE) showed that aggregation patterns were identified primarily in adult populations of both E. servus and N. viridula, and in nymphal populations of both species to a lesser extent. Aggregation patterns were also identified in early vegetative injury, but not in ear injury assessed at R2. The spatial association of stink bugs and their injury varied with corn phenological stage. A lack of spatial association between stink bug populations early in the season and vegetative injury suggests a need for intensive sampling, particularly in fields with increased residue from cover crops. Results of this study illustrate the variability in spatial patterns of stink bugs in corn, which can help to improve sampling plans for decision-making in IPM programs.

Epidemiology and Economic Impact of Impatiens Necrotic Spot Virus: A Resurging Pathogen Affecting Lettuce in the Salinas Valley of California.

The Orthotospovirus impatiens necrotic spot virus (INSV) is a thrips-transmitted pathogen of lettuce that has rapidly emerged as a serious threat to production in the Salinas Valley of Monterey County, California. As a first step toward understanding the severity of the virus, we utilized Spatial Analysis by Distance IndicEs (SADIE) to characterize the distribution and progression of INSV outbreaks and thrips infestations in two commercial lettuce fields. In both fields, INSV incidence rapidly increased from 15.86% ± 1.77 to 80.24% ± 2.60 over the course of 7 weeks and aggregated at specific edges in both fields as early as 3 weeks after planting (Ia = 1.63, Pa = 0.0100, and Ia = 1.53, Pa = 0.0300). In one of the fields, thrips populations aggregated in areas that also experienced the most INSV (Ia = 1.2435, Pa = 0.0400, week 3; Ia = 1.4815, Pa < 0.0001, week 6; Ia = 1.5608, Pa < 0.0001, week 9), while in the second field, thrips were distributed randomly despite the aggregated effects that were observed for INSV incidence. Economic analysis estimated that the virus accounted for over $475,000 in losses for the two fields, while stakeholder surveys documented over 750 fields that experienced INSV infection during the 2021 season in Monterey County alone. These studies enhance our knowledge on the epidemiology of thrips and INSV under current lettuce production practices in the Salinas Valley, while elucidating the economic consequences and broader challenges that are associated with managing thrips-transmitted viruses.

Size and location of host‐plant shape the spatial pattern of forest insect

Abstract Insect–host relationships can generate spatial patterns. The effect of plant species has been widely investigated, whereas the effect of plant size was ignored. The authors characterized the spatial pattern of the swift moth Endoclita excrescens Butler by combining spatial analysis by distance indices (SADIE) and spatial point pattern analysis (SPPA). Two contiguous plots of monospecific plantations of Manchurian ash Fraxinus mandshurica with different diameters at breast height (DBH) were sampled, and the position, DBH, and count of attack holes of each ash tree were recorded. The aggregation at the landscape scale is far stronger than those at the stand scale. At the landscape scale, trees with small number of bored holes were close to each other at distances of r &lt; 4 m. None of the significant patterns were found at the stand scale. SADIE results showed a strong association between count of attack holes and DBH at the landscape scale, whereas weak association at the stand scale. SPPA results showed that, either at the landscape or stand scale, the locations of ash trees were randomly distributed at small distance, but aggregated at large distance. The counts of holes are only dependent on the point (tree) at small distances (r &lt; 2.5 m) at the landscape scale. These results provide basic information for sampling and precision‐targeted controlling programs.

Characterization of the spatial distribution of the whitefly-transmitted virus complex in yellow squash fields in Southern Georgia, USA

A two-year study was conducted in 2019 and 2020 to characterize the spatial distribution of whitefly-transmitted virus complex (WTVC) in experimental and commercial yellow squash (Cucurbita pepo) fields in southern Georgia, USA. Field trials planted in Tifton, Georgia, USA were comprised of 30 rows of squash (variety: Gentry) divided into 300 quadrats. Six commercial fields in Tift, Worth, and Colquitt Counties in Georgia, USA were surveyed. In each field, 10 rows of plants per field were partitioned into 70 quadrats so that their approximate location could be mapped and disease incidence tracked in space over time. Plants in each quadrat were visually assessed for TVC symptoms at seven-day intervals (experimental fields) or at fourteen-day intervals (commercial fields). The spatial distribution of WTVC in a one-dimensional space was determined through ordinary runs analysis and in two-dimensional space through spatial autocorrelation analysis and spatial analysis by distance indices (SADIE). Ordinary runs analysis down and between rows suggested that disease was more likely to be transmitted from infected plants within rows than across rows. WTVC incidence in space was positively correlated with adult whiteflies on squash leaves taken one or two weeks prior to the assessment of virus incidence coinciding with latent period of Geminiviruses. SADIE generated disease severity maps indicated a shift from sparse and randomly distributed disease early in the infection cycle to denser, more aggregated patterns later in time in both experimental and commercial fields. Contour plots of interpolated indices from SADIE analysis suggested an edge effect on the spatial distribution of WTVC in experimental fields as well as in two of the commercial fields. An understanding of the shift from random to aggregated distribution and the edge effect on WTVC incidence are considerations for refining current management strategies.

Spatiotemporal Distribution of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) Across a Fruit and Tree Nut Agricultural Ecosystem.

The invasive brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is a mobile, polyphagous agricultural pest that feeds on a variety of plants. In orchard systems, seasonal monitoring of adults and nymphs in fruit and nut trees and noncrop host plants in surrounding habitat can be used to identify, in time and space, areas of high-density aggregations to develop targeted pest management strategies. We explored the spatiotemporal distribution of H. halys adults and nymphs and assessed whether seasonal distribution patterns varied according to habitat. From 2018 to 2021, pheromone-baited traps were placed in orchard and noncrop plants to first document the establishment of H. halys at this site and to describe seasonal development. In addition, stink bugs were monitored weekly during 2019-2020 across a grid of baited traps placed within the orchard ecosystem. Based on grid data, we used Spatial Analysis by Distance Indices (SADIE) to identify significant clusters of H. halys and visualized aggregations with interpolated maps. Overall, the distribution of H. halys adults and nymphs were similar; both aggregated primarily in peach and adjacent woodlands followed by pecan. Timing of aggregations was consistent across years and reached the highest levels in July and August. Moreover, we document that H. halys is an established pest within this orchard ecosystem, and that noncrop host plants likely play an important role in maintaining populations of H. halys. To manage H. halys in southeastern orchard systems, growers may need to account for host plants in habitats that surround fruiting trees.

Epidemiology of Grapevine Red Blotch Disease Progression in Southern Oregon Vineyards

Grapevine red blotch disease (GRBD) is an emerging disease caused by grapevine red blotch virus (GRBV). It is widespread in most United States winegrape production regions and differential spread dynamics have been reported between the regions. This study surveyed eight vineyard sites in southern Oregon over four years for the progression of GRBD incidence. The vineyards included five sites that were five years or older and three sites that were three-years-old. The disease incidence in the older blocks ranged from 2.81 to 58.78%, while in the younger blocks it ranged from 0.29 to 1.11%. Some vineyards implemented frequent disease scouting, removing infected vines and replanting. The disease incidence in these blocks remained &lt;5% over the survey period. However, in vineyards with no roguing and replanting, the disease incidence increased nearly 30-fold after three years. We analyzed the spatial distribution of the disease in vineyards surveyed in 2020 and found that the disease distribution is highly aggregated based on Spatial Analysis by Distance Indices (SADIE). In a separate study, we also tested the GRBV infection status of asymptomatic vines next to symptomatic vines to inform decision-making when roguing and replanting. Out of 410 asymptomatic vines surrounding 41 symptomatic vines, only two tested positive for GRBV. Additionally, in 2020 and 2021, we tested the GRBV status of previously identified possible alternative host species: blackberries (<i>Rubus armeniacus</i>) and wild/feral grapes (<i>Vitis</i><i>riparia</i>) collected from areas surrounding the four survey sites. GRBV was present in 10 to 70% of wild grape samples in both years and in 10% of the blackberry samples in 2020. However, the virus titer was low in blackberry samples and it was not detected in 2021 samples. These results indicate the potential importance of wild grapes as alternative hosts on GRBD incidence and spread in southern Oregon vineyards, while blackberry is unlikely to be an alternative host with epidemiological significance.

Spatiotemporal Distribution of Two Euschistus spp. Stink Bugs (Hemiptera: Pentatomidae) in Southeastern Farmscapes.

Stink bugs (Hemiptera: Pentatomidae) are ubiquitous, cryptic, phytophagous pests that are found in many crops. In agroecosystems, individuals disperse from adjacent noncrop hosts and tend to aggregate or cluster within fields. In this study, we characterized the distribution of Euschistus servus (Say) and Euschistus tristigmus (Say) (Hemiptera: Pentatomidae) over 2 yr at three southeastern United States farmscapes. Stink bugs were captured in pheromone-baited traps, and Spatial Analysis by Distance Indices (SADIE) used to identify the location of significant aggregations by habitat type and season. Euschistus servus adults were more likely to be captured in pecan orchards, cotton, other crops, or unmanaged habitats than in woodland habitats. Significant aggregations of E. servus were detected in a variety of habitats including pecan, corn, cotton, peanut, and tobacco, as well as fallow and hay fields, pastures, and hedgerows. Fewer adult E. tristigmus were captured than E. servus adults, and E. tristigmus adults were typically trapped and aggregated in woodland habitats. The resulting data provide an important understanding regarding the seasonal movement and relative abundance levels of stink bug populations, which are critical to the development of integrated pest management strategies.

Characterizing the Spatiotemporal Distribution of Three Native Stink Bugs (Hemiptera: Pentatomidae) across an Agricultural Landscape.

Simple SummaryStink bugs (Hemiptera: Pentatomidae) are highly mobile pests that forage on, and damage, a variety of crops. Habitats that surround farms, such as forests, wetlands, and pastures may play a role in the location of stink bugs and their movement into crop fields. Here, stink bugs were trapped weekly across an 18 km2 agricultural landscape, and we characterized their distribution, as well as patterns of aggregation by habitat. Brown stink bugs (Euschistus servus) were most often captured in crop fields and the timing of aggregations often corresponded to food availability. Dusky stink bugs (Euschistus tristigmus) were primarily captured in forest, and only occasionally in crop fields. Green stink bugs (Chinavia hilaris) were found in both crop fields and non-crop habitat. Control of stink bugs may require management plans that consider movement not only within crop fields, but also the surrounding habitat.Stink bugs (Hemiptera: Pentatomidae) are polyphagous pests that cause significant economic losses to a variety of crops. Although many species have been documented to aggregate within agricultural fields, much less is known regarding the timing and distribution of adults and nymphs within and between surrounding non-crop habitat. Therefore, we explored the spatiotemporal distribution of Euschistus servus (Say), Euschistus tristigmus (Say), and Chinavia hilaris (Say), three species of North American origin, and examined whether distribution patterns varied between species according to habitat. Stink bugs were monitored weekly for three years within an 18 km2 grid of pheromone-baited traps. We tested whether habitat affected distribution patterns, used spatial analysis by distance indices (SADIE) to identify aggregations, and visualized distributions with interpolated maps. Overall, E. servus adults were captured in crops, whereas E. tristigmus adults and nymphs were mainly captured in forests. Accordingly, distribution patterns of E. tristigmus were relatively stable over time, whereas aggregations of adult E. servus varied over space, and the timing of aggregations reflected the phenology of major crops. Chinavia hilaris was most often captured in forest, followed by crop habitat. Pest management strategies for stink bugs may require an area-based management approach that accounts for movement in agricultural fields and surrounding habitat.

Spatial Associations of Key Lepidopteran Pests With Defoliation, NDVI, and Plant Height in Soybean

In soybean, Glycine max (L.) Merrill, production, losses to, and control costs for insect pests can be significant limiting factors. Although the heterogeneity of pests has typically been ignored in traditional field management practices, technological advancements have allowed for site-specific pest management systems to be developed for the precise control of pests within a field. In this study, we chose to determine how the in-field distributions of the larvae of three major lepidopteran pests [velvetbean caterpillar Anticarsia gemmatalis (Hübner) (Lepidoptera: Erebidae), soybean looper Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), and green cloverworm Hypena scabra (Lepidoptera: Erebidae) (Fabricius)] were spatially associated with defoliation, Normalized Difference Vegetation Index (NDVI), and plant height in soybean. Spatial analysis by distance indices (SADIE) of data from two South Carolina soybean fields in 2017 and 2018 revealed a limited number of spatial aggregations for insect datasets. However, 14% and 6% of paired plant-insect datasets were significantly associated or dissociated, respectively. NDVI was found to be more associated with pest distributions than soybean plant heights and defoliation estimates, and the majority of all plant-insect associations and dissociations occurred in the first 4 wk of sampling (late July-early August). If changes are to be implemented regarding how a pest is managed, critical factors explaining the spatial distribution of pests must be identified. Results from this study advocate for the relationship between early-season distributions of pests and important plant variables such as NDVI to be further investigated to better determine the strength of the correlations across years and sites.

Spatial and temporal population dynamics of male and female Aedes albopictus at a local scale in Medell\xedn, Colombia

BackgroundDiseases transmitted by invasive Aedes aegypti and Aedes albopictus mosquitoes are public health issues in the tropics and subtropics. Understanding the ecology of mosquito vectors is essential for the development of effective disease mitigation programs and will allow for accurate predictions of vector occurrence and abundance. Studies that examine mosquito population dynamics are typically focused on female presence or total adult captures without discriminating the temporal and spatial distribution of both sexes.MethodsWe collected immature and adult mosquitoes bimonthly for 2 years (2018–2019) in the Medellín Botanical Garden. Collection sites differed in proximity to buildings and nearby vegetation, and were classified by their overhead vegetation cover. We used linear mixed models (LMMs) and Spatial Analysis by Distance Indices (SADIE) to assess the spatial distribution of Ae. aegypti and Ae. albopictus. Using our Ae. albopictus captures exclusively, we assessed (1) the spatial and temporal distribution of males and females using SADIE and a generalized linear mixed model (GLMM), (2) the relationship between climatic variables/vegetation coverage and adult captures using GLMMs and LMMs, and (3) the correlation of male and female size in relation to climatic variables and vegetation coverage using LMMs.ResultsSpatial analysis showed that Ae. aegypti and Ae. albopictus were distributed at different locations within the surveilled area. However, Ae. albopictus was the predominant species in the park during the study period. Adult Ae. albopictus captures were positively correlated with precipitation and relative humidity, and inversely correlated with temperature and wind speed. Moreover, we observed a spatial misalignment of Ae. albopictus males and females—the majority of males were located in the high vegetation coverage sites, while females were more evenly distributed. We observed significant associations of the size of our adult Ae. albopictus captures with precipitation, temperature, and wind speed for both sexes and found that overhead vegetation cover influenced male size, but observed no effect on female size.ConclusionsOur work elucidates the differential dynamics of Ae. albopictus males and females, which is pivotal to develop accurate surveillance and the successful establishment of vector control programs based on the disruption of insect reproduction.Graphical

Spatio-temporal distribution of Ricania shantungensis (Hemiptera: Ricaniidae) in chestnut fields: Implications for site-specific management

• Spatial distributions of R. shantungensis were aggregated and consistent in chestnut fields. • Site-specific management for R. shantungensis would be applicable in chestnut fields. • For application of site-specific management, additional 60 m should be considered with a target management area. Chestnut is one of most important forest products in Korea. However, Ricania shantungensis , an invasive species, has been increasingly causing economic damage to chestnut. To increase management efficiency of R. shantungensis in chestnut fields, its spatio-temporal distributions were analyzed using spatial analysis by distance indices (SADIE) and semivariogram. Experiments were conducted by observing selected, marked, and geo-referenced trees in two commercial chestnut fields for each developmental stage (i.e., spring egg, nymph, adult, and fall egg) of R. shantungensis from 2017 to 2019. Spatial distributions of R. shantungensis were statistically ( P < 0.05) aggregated except for its nymphal stage. Spatial associations of its distributions also showed the statistically ( P < 0.05) positive associations regardless of years or developmental stages except for the spatial relationship between egg and nymphal stages. These results indicated that site-specific management for R. shantungensis would be applicable. In application of site-specific management for R. shantungensis , the distance of spatial dependence for nymphs, 60 m, should be considered to minimize reoccurrence possibility and additional samplings. Incorporating site-specific management into pest control program of R. shantungensis could increase its control efficiency in chestnut fields.

Spatial distribution of Cydia pomonella (Lepidoptera: Tortricidae) populations and its relation with topographic variables

In this study the spatial distribution of codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae) and its relation with topographic variables were investigated. The study was conducted during three growing seasons, 2017–2019. The activity of adult males was monitored using delta-shaped traps baited with sex pheromone. Forty-five traps set at 50–200 m intervals were placed within a 12 ha orchard in 2017, and 30 traps set at 684–7560 m intervals were placed in 30 orchards in 2018 and 2019. The mature larvae were sampled using a 15 cm wide hemp wrapped around 113 tree trunks in three orchards during 2019. Spatial analysis by distance indices (SADIE) was used to determine spatial distribution of adults and larvae. According to the results, adult males of codling moth had significant and stable aggregated distribution during population peaks at local scale, but not at regional scale. Mature larvae populations showed random distribution pattern in the studied orchards. The relation between insect abundance and topographic variables was investigated using spatial regression analysis, and no significant correlation was determined. The findings of this study can be used for spatial forecasting and management of codling moth at local and regional scales.

Characterization of the spatial distribution of alfalfa weevil, Hypera postica, and its natural enemies, using geospatial models.

BACKGROUNDUnderstanding the spatio‐temporal dynamics of prey and predator distributions can provide valuable insights into pest management strategies and conservation of natural enemies in agro‐ecosystems. The alfalfa weevil, Hypera postica (Gyllenhal), is an economically important pest of alfalfa throughout the western United States. Coccinellids and nabids are among the most important natural enemies of this species, contributing to the biological control of H. postica in alfalfa fields. The spatio‐temporal dynamics of H. postica and these two predator groups were investigated using 81 (= 9 × 9 grid) sample points in each of five alfalfa fields in north‐central Montana. The data were analyzed using variogram and spatial analysis by distance indices (SADIE).RESULTSVariogram analysis revealed the spatial dependence (aggregation) of H. postica in 17 of 19 sampling times for larvae, and three of 12 sampling times for adults. Using SADIE, statistically significant aggregation distribution was evident in four of 19 sampling times for larvae, and five of 12 sampling times for adults of H. postica. Combined variogram and SADIE showed strong evidence of spatial aggregation of H. postica larval population (~95%) while a moderate level of aggregation in the adult population (~67%) of the sampling times analyzed. The average aggregation distances based on the range value of the variogram were 22.3 m and 14.7 m for larvae and adults, respectively. Based on variogram results, populations of natural enemies, coccinellids and Nabis spp. were found spatially aggregated in 57.9% and 5.6% of the sampling times, respectively. SADIE further supported the variogram results as coccinellid populations (52.6% of sampling times) were highly aggregated in contrast with the Nabis spp. populations (5.6% of sampling times) in alfalfa fields. There was no evidence of significant spatial synchrony between H. postica and its predators, coccinellids and Nabis spp.CONCLUSIONOur study was able to determine the spatial and temporal distribution of H. postica and its two natural enemies (coccinellids and nabids) in irrigated alfalfa fields. The possible implications of these findings for integrated pest management (IPM) of alfalfa weevil populations are discussed.

Spatial and spatiotemporal analysis of Meloidogyne hapla and Pratylenchus penetrans populations in commercial potato fields in New York, USA

Summary Meloidogyne hapla and Pratylenchus penetrans are important plant-parasitic nematodes affecting potato in New York and the Northeastern United States, yet little is known of their spatial patterns and spatiotemporal dynamics. Spatial patterns of M. hapla and Pratylenchus spp. were quantified using semivariogram analysis and Spatial Analysis by Distance IndicEs (SADIE). Nematode populations were assessed within each of three commercial potato fields in 2016 and 2017, with fields sampled on two occasions in-season. Semivariogram analysis and ordinary kriging indicated initial population densities to be spatially dependent over an average range of 110 m for M. hapla and 147 m for Pratylenchus spp. SADIE indicated Pratylenchus spp. to be significantly aggregated in nearly all fields (10 of 12 samplings, to 2.113). Meloidogyne hapla populations were aggregated in only three of 12 samplings ( to 1.738). Spatiotemporal analysis using the association function of SADIE indicated a strong and significant association between initial and final population densities of M. hapla and Pratylenchus spp. within fields. This information is fundamental for the development of enhanced sampling protocols for estimation of plant-parasitic nematodes and evaluating the feasibility of site-specific nematicide application in New York potato fields.

Landscape agricultural simplification correlates positively with the spatial distribution of a specialist yet negatively with a generalist pest

Agricultural expansion at the cost of natural or semi-natural habitats is simplifying human-dominated landscapes. As croplands provide a large resource of food to herbivores, pest damage may increase, but such large-scale patterns across regions are little known. Here, we used two years of maize field data from 102 counties (each 1318 km2 on average) across Shandong Province in China to study the spatial distribution of two major co-occurring maize pests: the putative habitat specialist the Asian Corn Borer (Ostrinia furnacalis) (ACB) and the generalist Yellow Peach Moth (Conogethes punctiferalis) (YPM). We used Spatial Analysis by Distance Indices (SADIE) to assess the spatial distribution patterns of these pests and their relation to landscape factors. In both 2016 and 2017, the aggregation and abundance of the ACB was positively correlated with the proportion of maize on the county level, whereas the YPM exhibited the opposite pattern, i.e., a negative correlation with maize proportion. The ACB abundance was below the economic threshold level when maize was <31% in 2017, whereas the YPM abundance was below the threshold when maize was >27% (in 2016) or 23% (in 2017). Maize plant presence was the main determinant of the abundance of the ACB, while the YPM appeared to benefit from further resources in non-crop habitats. These contrasting distribution patterns suggest that the two pests are driven by their different resource requirements. In more diversified landscapes, pest control may need to focus primarily on the generalist consumer, the YPM, whereas in maize-dominated landscapes, the specialist consumer, the ACB, is dominant and needs attention.

Does Harvesting Affect the Spatio-Temporal Signature of Pests and Natural Enemies in Alfalfa Fields?

Determining the spatio-temporal distribution and association of pests and natural enemies would be useful for implementing biological control of pests and could also be used in site-specific pest management. In this study, the spatio-temporal distribution and association of aphids, plant bugs, and natural enemies were assessed in alfalfa fields using geo-statistics and spatial analysis by distance indices (SADIE). Additionally, the effect of alfalfa hay-harvesting on the spatial and temporal distribution of these insects was investigated for the first time. Geostatistical analysis indicated that the degree of dependence (DD) was ≥75% for 11 out of 39, 9 out of 35, 3 out of 12, 10 out of 29, and 2 out of 20 datasets for pea aphid Acyrthosiphon pisum, spotted alfalfa aphid Therioaphis maculata, cowpea aphid Aphis craccivora, alfalfa plant bug Adelphocoris lineolatus, and tarnished plant bug Lygus rugulipennis, respectively. The results also indicated that DD was ≥75% in 7 out of 45, 18 out of 45, and 3 out of 20 datasets for Coccinella septempunctata, Hippodamia variegata, and Pterostichus melanarius, respectively. Harvesting decreased the aggregation of the ladybirds, which resulted in a decrease in the index of aggregation. The geo-statistics results were confirmed by SADIE in 75% of datasets. These results can be used in biological control and site-specific management of aphids and plant bugs in alfalfa fields.

Spatiotemporal association between the mite Brevipalpus yothersi and Citrus leprosis virus C in orange orchards.

Citrus leprosis virus C (CiLV-C) is an economically important pathogen and the main causative agent of leprosis disease in citrus orchards. The main vector of this disease, the mite Brevipalpus yothersi, is widely distributed in Mexican orchards on a wide range of citrus species. Despite the importance of both the virus and the mite, field studies recording their occurrence and co-occurrence are practically non-existent. We systematically sampled orange orchards for both CiLV-C and B. yothersi throughout the year. The distribution of the CiLV-C and B. yothersi was evaluated on each sampling occasion and their spatiotemporal associations were determined. Specifically, 100-112 orange trees, distributed in 18 rows (five or six trees per row), were sampled monthly between March 2017 and February 2018 (11 sampling dates). Twenty leaves per tree were sampled on each occasion. The number of mites per tree and the percentage of leaves per tree with disease symptoms were recorded. On each sampling occasion, spatiotemporal associations between mites and disease were determined using the Spatial Analysis by Distance Indices (SADIE) method. CiLV-C and B. yothersi were identified using molecular methods. Throughout the study, the distribution of CiLV-C was aggregated and the distribution of B. yothersi was random. No association was found between the virus and the mite on any of the sampling dates. In total, 173 mites were collected, but only 43 mites were found to be carrying CiLV-C. The reason for this lack of association between the virus and the mite, as well as the impact of our findings on the epidemiology of the disease in orange orchards, are discussed.