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Bemisia tabaci is a whitefly species complex comprising important phloem feeding insect pests and plant virus vectors of many agricultural crops. Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) are the two most invasive members of the B. tabaci species complex worldwide. The diversity of agroecosystems invaded by B. tabaci could potentially influence their population structure, but this has not been assessed at a farmscape level. A farmscape in this study is defined as heterogenous habitat with crop and non-crop areas spanning ~8 square kilometers. In this study, mitochondrial COI gene (mtCOI) sequences and six microsatellite markers were used to examine the population structure of B. tabaci MEAM1 colonizing different plant species at a farmscape level in Georgia, United States. Thirty-five populations of adult whiteflies on row and vegetable crops and weeds across major agricultural regions of Georgia were collected from fifteen farmscapes. Based on morphological features and mtCOI sequences, five species/cryptic species of whiteflies (B. tabaci MEAM1, B. tabaci MED, Dialeurodes citri, Trialeurodes abutiloneus, T. vaporariorum) were found. Analysis of 102 mtCOI sequences revealed the presence of a single B. tabaci MEAM1 haplotype across farmscapes in Georgia. Population genetics analyses (AMOVA, PCA and STRUCTURE) of B. tabaci MEAM1 (microsatellite data) revealed only minimal genetic differences among collected populations within and among farmscapes. Overall, our results suggest that there is a high level of gene flow among B. tabaci MEAM1 populations among farmscapes in Georgia. Frequent whitefly population explosions driven by a single or a few major whitefly-suitable hosts planted on a wide spatial scale may be the key factor behind the persistence of a single panmictic population over Georgia's farmscapes. These population structuring effects are useful for delineating the spatial scale at which whiteflies must be managed and predicting the speed at which alleles associated with insecticide resistance might spread.

The analysis of molecular variance (AMOVA) revealed that most of the genetic variance was partitioned within populations (among and within individuals of a population) (Table 9). The variance partitioned among B. tabaci MEAM1 populations from different farmscapes and host plants was 2.00% (Table 9). Overall, AMOVA results suggested that there were no significant genetic differences among populations. Mantel test results revealed no correlation between genetic and geographic distances among populations (r2 = 0.0008, p = 0.429).

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Hierarchical analysis of molecular variance (AMOVA) for the 35 B. tabaci MEAM1 populations collected from Georgia, USA, based on six microsatellite markers. (A) Among populations collected from different host plants. (B) Among populations collected from different farmscapes.

Bayesian clustering analysis results for 35 B. tabaci MEAM1 populations based on six microsatellite markers using STRUCTURE v.2.3.2. (A) Optimal number of genetic clusters (K = 3) following methods described by Evanno et al. 2005. (B) Plot of average likelihood L(K) and variance per K. (C) Scatter plots at K = 3. The length of each line in the bars represents the proportion of the genome in different clusters. Whitefly populations collected from different host plants or farmscapes are separated by a continuous vertical black line.

Population structure based on principal component analysis for B. tabaci MEAM1 populations collected from different host plants (A), and farmscapes (B). Dots represent single individuals within the populations. All individuals are clustered together indicating minimum genetic isolation between individuals.

The citrus whitefly, D. citri is a serious citrus pest in Florida [63]. However, it is seldom considered a pest in vegetables and row crops in Georgia. Bandedwinged whiteflies, T. abutiloneus, and B. tabaci MEAM1 were present in all farmscapes, but B. tabaci MEAM1 was far more abundant than T. abutiloneus. Trialeurodesabutiloneus is native and widely distributed throughout United States. Although distributed throughout the farmscapes of Georgia, T. abutiloneus rarely reaches numbers that justify treatment with insecticides. The greenhouse whitefly, T. vaporariorum, was found on field-grown squash in Spalding county. There is growing evidence that T. vaporariorum may not necessarily be limited to greenhouse environments [64,65]. However, in the current study, T. vaporariorum was found in just one squash field located near urban landscapes. Therefore, the T. vaporariorum individuals that were collected might have dispersed into the squash field from a nearby greenhouse. Trialeurodes is the only whitefly genus other than Bemisia that has been documented as a plant virus vector [66]. Both T. abutiloneus and T. vaporariorum are reported vectors of plant viruses in the family Closteroviridae [65,66]. Bemisia tabaci MED cryptic species was found in snap bean and eggplant fields in Clarke and Spalding counties located in North Georgia, respectively. At both locations, MED individuals were present in the same field as MEAM1 and were limited in number (

Genetic differentiation (pairwise FST) between B. tabaci MEAM1 populations collected from different host plants or farmscapes was very low. Likewise, results from population structure analysis (AMOVA, STRUCTURE, and PCA) did not suggest evidence of host- or farmscape-specific genetic clustering. Furthermore, a test of isolation by distance (Mantel test) indicated no correlation between genetic differentiation and geographic distance among all populations. Taken together, results suggest that there could be extensive gene flow among whitefly populations inhabiting various crops and farmscapes aided by frequent wind-aided dispersal and high spatial synchrony among B. tabaci populations across farmscapes [72,73]. Low genetic diversity among B. tabaci MEAM1 populations observed in the current study could also be influenced by population bottlenecks, founder effects, or high mortality caused by insecticides [34,74,75]. Invasive insects such as B. tabaci MEAM1 often experience genetic bottlenecks that can lead to low genetic diversity [74,76]. In the current study, only one out of 13 populations collected from different host plants and one out of 15 populations collected from different farmscapes exhibited evidence of a genetic bottleneck. Overall, there was no substantial evidence for bottleneck effects driving the low genetic differentiation observed among B. tabaci MEAM1 populations in Georgia. Nevertheless, the heterozygote excess associated with population bottlenecks is not expected to last more than few generations [77]. This signature could rapidly erode in insects such as B. tabaci, which have high reproductive potential and can complete multiple generations (up to 12 in Georgia, United States) within a single calendar year [30]. Thus, signatures associated with earlier population bottleneck effects influencing B. tabaci MEAM1 populations since its introduction to the United States in the 1980s might not have been captured in this study.

Bemisia tabaci population genetic analyses carried out at fine spatial scales with no major geographical barriers tend to show no or minimal genetic differences among populations [32,78,79]. However, studies carried out over large geographical areas have reported substantial population structure [31,80]. These studies suggest that B. tabaci populations tend to cluster between regions isolated by geographical barriers. Results in this study are in agreement with earlier reports; the low level of genetic diversity observed in the current study might be influenced by lack of geographical barriers between populations. Furthermore, cropping patterns in Georgia might have also contributed to the low genetic differentiation in B. tabaci MEAM1 populations. In Georgia, summer cotton is planted within a rotation of spring, fall, and winter vegetable crops [81,82], essentially providing suitable host plants for B. tabaci MEAM1 year-around. Cotton is one of the most widely grown crops in Georgia; approximately 1.4 million acres of cotton were planted in 2019 [83]. Widespread availability of susceptible hosts and higher temperatures during the summer allow whiteflies to reproduce extensively, and cotton defoliation could trigger mass dispersal of whiteflies from cotton into fall-planted vegetable crops and also weeds. Over the years, this annual dispersal of whiteflies from cotton to nearby vegetation might have resulted in the genetic uniformity among B. tabaci MEAM1 populations across farmscapes.

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Parasitism and predation of stink bug eggs were evaluated in sorghum trap crops located in Irwin Co., GA. The study was conducted in a corn-cotton farmscape in 2002 and 2006, 4 corn-cotton and peanut-cotton farmscapes in 2004, and 3 peanut-cotton farmscapes in 2005. The experimental design and sampling scheme for the 2002 egg study were the same as previously described for the 2002 trap crop experiment, and the experimental design and sampling scheme for the 2004, 2005, and 2006 egg studies were the same as previously described for the 2004 trap crop experiments (Tillman 2006). All recommended agricultural practices for production of sorghum were followed (Mask et al. 2010, -0502). No insecticides were applied for pest insects during the experiments.

In the southeast United States, a field of peanuts, Arachis hypogaea L., is often closely associated with a field of cotton, Gossypium hirsutum L. The objective of this 4-yr on-farm study was to examine and compare the spatiotemporal patterns and dispersal of the southern green stink bug, Nezara viridula L., and the brown stink bug, Euschistus servus (Say), in six of these peanut-cotton farmscapes. GS+ Version 9 was used to generate interpolated estimates of stink bug density by inverse distance weighting. Interpolated stink bug population raster maps were constructed using ArcMap Version 9.2. This technique was used to show any change in distribution of stink bugs in the farmscape over time. SADIE (spatial analysis by distance indices) methodology was used to examine spatial aggregation of individual stink bug species and spatial association of the two stink bug species in the individual crops. Altogether, the spatiotemporal analyses for the farmscapes showed that some N. viridula and E. servus nymphs and adults that develop in peanuts disperse into cotton. When these stink bugs disperse from peanuts into cotton, they aggregate in cotton at the interface, or common boundary, of the two crops while feeding on cotton bolls. Therefore, there is a pronounced edge effect observed in the distribution of stink bugs as they colonize the new crop, cotton. The driving force for the spatiotemporal distribution and dispersal of both stink bug species in peanut-cotton farmscapes seems to be availability of food in time and space mitigated by landscape structure. Thus, an understanding of farmscape ecology of stink bugs and their natural enemies is necessary to strategically place, in time and space, biologically based management strategies that control stink bug populations while conserving natural enemies and the environment and reducing off-farm inputs. 9af72c28ce