Evaluation of various deployment strategies of imidacloprid-treated spheres in highbush blueberries for control of Rhagoletis mendax (Diptera: Tephritidae)

Biodegradable, ammonium-baited spheres treated with the neonicotinoid insecticide Provado (imidacloprid) at 2% (AI) were evaluated for controlling blueberry maggot flies, Rhagoletis mendax Curran. Three strategies for sphere deployment in highbush blueberries, Vaccinium corymbosum L., were compared with untreated control plots in 1999 and once again compared against control plots and organophosphate insecticide sprays in 2000. The patterns of sphere deployment were as follows: (1) perimeter deployment in which spheres were hung individually and spaced equally around the perimeter of experimental plots; (2) cluster deployment in which four groups of three spheres were hung in equally spaced perimeter locations of experimental plots; and (3) uniform deployment in which spheres were placed 10 m apart (in a grid-like pattern) within experimental plots. In 1999, there were no significant differences in fruit injury levels based on observed R. mendax oviposition scars and reared larvae among plots containing imidacloprid-treated spheres in perimeter, cluster, and internal-grid patterns. However, all plots containing spheres had significantly lower fruit infestation levels (<2%), compared with unsprayed control plots with no spheres deployed, which had infestation levels (>20%). In 2000, there were no significant differences in fruit injury based on observed R. mendax oviposition scars between plots containing imidacloprid-treated spheres in the three deployment strategies tested and plots that received Guthion (Azinphosmethyl) spray applications. However, significantly fewer R. mendax larvae were reared from berries collected from plots that received two applications of Guthion compared with plots in which imidacloprid-treated spheres were deployed. Irrespective of sphere deployment strategies, all sphere-treated and sprayed plots had significantly lower injury levels (<1.5%), based on numbers of reared larvae compared with berries collected from the control plots (>4.0%). Based on captures of flies on unbaited Pherocon AM boards placed in the center of treatment plots, we observed a suppression of R. mendax in plots containing imidacloprid-treated spheres compared with control plots. The potential of using imidacloprid-treated spheres as a behavioral control integrated pest management tactic for blueberry maggot flies is discussed.     

Kaolin affects blueberry maggot behavior on fruit

This study assessed the effects of Surround (kaolin) on several behavioral parameters of female blueberry maggot, Rhagoletis mendax Curran (Diptera: Tephritidae). First fruit visited, walking, cleaning, and oviposition behavior were quantified in two-choice and no-choice assays where females encountered Surround-treated and untreated fruit of highbush blueberries (Vaccinium spp.). In two-choice assays, females had a propensity (68%) to first visit untreated blueberries. In two-choice and no-choice tests, number of walking bouts and duration of walking bouts were significantly shorter on the Surround-treated than on untreated fruit. Few oviposition attempts on fruit were observed, irrespective of treatments and assays. Chromameter measurements showed significant modification of the blueberry skin color parameters lightness, hue, and saturation between untreated fruit compared with fruit dipped once or twice in a suspension of Surround. Oviposition trials with field-treated fruit showed that blueberries treated with Surround had fewer oviposition scars than the control, and this was more pronounced with weekly applications of Surround. Uneven coating of the fruit by Surround in field applications may have resulted in higher acceptance rates by flies than in blueberries individually dipped and used in laboratory trials.     

Evaluation of Vaccinium spp. for Illinoia pepperi (Hemiptera: Aphididae) performance and phenolic content

Host acceptance and population parameters of the aphid Illinoia pepperi (MacGillivray) (Hemiptera: Aphididae) were measured on highbush blueberry, Vaccinium corymbosum L. 'Elliott', and the wild species Vaccinium boreale Hall and Aalders, Vaccinium tenellum Aiton, Vaccinium pallidum Aiton, Vaccinium hirsutum Buckley, Vaccinium myrsinites Lamarck, and Vaccinium darrowi Camp. After 24 h of exposure, significantly fewer aphids remained in contact with V. boreale and V. hirsutum compared with V. corymbosum Elliott, V. darrowi, and V. pallidum. Length of the prereproductive period of I. pepperi was significantly longer on V. boreale and V. myrsinites, in contrast to V. corymbosum. Fecundity was also lower on V. boreale, V. hirsutum, V. myrsinites, and V. darrowi. Survivorship of I. pepperi 42 d after birth was significantly lower on V. hirsutum compared with the remaining Vaccinium spp. Reduced I. pepperi performance resulted in significantly lower intrinsic rate of increase (r(m)) values being associated with V. myrsinites, V. boreale, V. hirsutum, and V. darrowi, compared with V. corymbosum. Net reproductive rate (R(o)), generation time (T), and doubling time (T(d)) of I. pepperi also were affected by the Vaccinium spp. Total phenolic and flavonol content varied between Vaccinium spp., with some high phenolic content Vaccinium spp. having reduced aphid performance. However, no significant correlation between phenolics and I. pepperi performance was detected. Results from this study identified several potential sources of aphid resistance traits in wild Vaccinium spp.     

Emergence of blueberry maggot flies (Diptera: tephritidae) from mulches and soil at various depths

Control of blueberry maggot, Rhagoletis mendax Curran, typically is achieved with insecticides targeting adult flies before females oviposit in ripening fruit. Management strategies targeting other life stages have received less attention. We tested effects of compost or pine needle mulches on emergence of blueberry maggot flies under laboratory and field conditions. Few flies emerged from pupae that were buried under 20 cm of pine needles in all experiments, but burial in 20 cm of compost did not always result in low fly emergence. Burial of pupae in 5 cm of compost or pine needles did not reduce fly emergence compared with 1 cm in soil. Low emergence with increased mulch depth appeared to be primarily because of failure of flies to ascend to the surface after they exited puparia. Low emergence also was associated with high moisture levels causing rotten, discolored pupae, particularly in the laboratory in compost. No flies emerged from pupae buried in 1 cm of pine needles in the field. In this case no flies exited puparia, likely because high temperatures (>30°C) at the surface killed pupae. Thus, mulch application under highbush blueberries (Vaccinium corymbosum L.) after maggots drop from berries can reduce emergence success of flies from buried pupae, but the level of control will depend on mulch depth and may vary with rainfall and temperature.     

Infection of wild and cultivated Vaccinium spp. with blueberry leaf mottle nepovirus

A field survey was performed during the summers of 1991 and 1992 to determine whether blueberry leaf mottle virus (BLMV) infects wild blueberry bushes surrounding commercial blueberry fields and might act as a reservoir of the virus. Leaf samples from wild blueberries growing in wooded areas surrounding commercial plantings in Western central Lower Michigan were taken from bushes radiating out from the border of the commercial field into the wooded areas at 5, 50 and 100 m. BLMV was present in native bushes of Vaccinium corymbosum, V. myrtilloides and V. angustifolium, and two hybrids of V. corymbosum V. angustifolium. BLMV-infected pollen grains were detected in pollen traps located up to 2 miles from a source field.     

蓝浆果花冠形态特征及其与果实横径相关性的分析

对兔眼蓝浆果（Vaccinium ashei Reade）、北方高丛蓝浆果（V.corymbosum L．）和南方高丛蓝浆果（V.corymbosum hybrids）3个品种群及南方高丛蓝浆果实生系的花冠长度、花冠宽度、花冠长宽比和花冠口径大小等特征进行了测定和比较,并研究了花冠形态特征参数与果实横径的相关性。研究结果表明,蓝浆果不同品种群间和同一品种群内不同品种间的花冠形态特征参数差异较大;依据花冠形态特征参数,可将供试的兔眼蓝浆果和南方高丛蓝浆果各品种及南方高丛蓝浆果各实生系初步划分为4种类型,将供试的北方高丛蓝浆果各品种划分为3种类型。此外,只有南方高丛蓝浆果各品种及其实生系的果实横径与花冠宽度相关性显著（P〈0．05）,相关系数分别为0．639和0．324。     

Distribution and phenology of Dasineura oxycoccana (Diptera: Cecidomyiidae) in Michigan blueberries

The blueberry gall midge, Dasineura oxycoccana Johnson, is a serious pest of rabbiteye blueberries in Florida, Georgia, and Mississippi, and a potential pest of southern and northern highbush blueberries. Its damage has been observed with increasing frequency in highbush blueberry plantings in the Great Lakes region, including in Wisconsin and in Michigan. Unlike in rabbiteye blueberry plantings, where blueberry gall midge primarily damages flowering buds, it is found to damage only the vegetative shoots of northern highbush blueberry. In this study, farms throughout Michigan were surveyed for the presence of blueberry gall midge and it was found in 43 of 46 sampled farms in 11 counties. From 2009-2011, several monitoring techniques, including yellow sticky traps, emergence traps, observational sampling, and vegetative shoot dissections were used to determine the ecology of this species in blueberry fields in southwest Michigan. Emergence traps were most useful in early detection of blueberry gall midge in April, and observational sampling for damage symptoms and vegetative shoot dissections revealed multiple population peaks throughout July and August. Infestation was detected in vegetative shoot tips in all parts of the bushes, with initial infestation greatest at the base of bushes. Degree day accumulations until first midge detection and peak infestation suggest some potential for predicting key events in the pest's phenology. This information about the distribution and timing of infestation will be useful in developing management strategies for blueberry gall midge infestation.     

Phenology of Dasineura oxycoccana (Diptera: Cecidomyiidae) on cranberry and blueberry indicates potential for gene flow

Dasineura oxycoccana (Johnson) (Diptera: Cecidomyiidae) is a pest of cranberry, Vaccinium macrocarpon (Aiton) (Ericales: Ericaceae), and highbush blueberry, Vaccinium corymbosum (L.) (Ericales: Ericaceae), in North America. In British Columbia, Canada, D. oxycoccana was first found on highbush blueberry in 1991 and then on cranberry seven years later. Because many cranberry and highbush blueberry farms are adjacent to one another, we hypothesized that D. oxycoccana was moving from highbush blueberry onto cranberry. Cranberry and highbush blueberry differ in phenology, and adaptation to these different phenologies may result in host races or cryptic species on these two crops. We recognized the alternative hypothesis that D. oxycoccana had arrived as immature stages with cranberry vines imported from another region of North America. During spring and summer, we recorded the phenology of D. oxycoccana and the development of plant shoots from three cranberry and three highbush blueberry farms to determine whether the opportunity exists for successful movement of D. oxycoccana between the two crops. Our results show that D. oxycoccana from cranberry and highbush blueberry overlap in phenology for much of the season, indicating a high potential for movement and gene flow. However, differences were seen in number of larvae per shoot, location of pupae, and heat unit accumulation during larval development suggesting that instead there may be the potential for host race or cryptic species formation.     

Effects of southern highbush blueberry cultivar and treatment threshold on flower thrips populations

In Florida, southern highbush (SHB) blueberries (Vaccinium corymbosum L. x Vaccinium darrowi Camp) are grown for a highly profitable early season fresh market. Flower thrips are the key pest of SHB blueberries, and Frankliniella bispinosa (Morgan) is the most common species found. Flower thrips injure blueberry flowers by feeding and ovipositing in all developing tissues. These injuries can lead to scarring of developing fruit. The objectives of this study were to determine the relationship between thrips and yield in different SHB blueberry cultivars and to determine an action threshold. Experiments were conducted during early spring 2007 and 2008 on four farms; a research farm in Citra, FL; and three commercial farms, two in Hernando Co., FL., and one in Lake Co., FL. At the Citra farm, 'Emerald', 'Jewel', 'Millennia', and 'Star' blueberries were compared in 2007, and all but Star were compared in 2008. On the Hernando and Lake Co. farms, two treatment thresholds (100 and 200 thrips per trap) and an untreated control and four cultivars (Emerald, Jewel, Millennia, and 'Windsor') were compared. Emerald consistently had more thrips per trap and per flower than the other cultivars on all four farms. However, this did not always lead to an increase in fruit injury. Thrips numbers exceeded the threshold on only one farm in 2007, and there was a significantly lower proportion of injured and malformed fruit in the 100 thrips per trap threshold treatment compared with the control on this farm.     

Protection of fruit against infestation by apple maggot and blueberry maggot (Diptera: Tephritidae) using compounds containing spinosad

Two insecticide formulations containing the naturalyte insecticide spinosad, GF-120 Fruit Fly Bait and SpinTor 2 SC, were compared for control of apple maggot, Rhagoletis pomonella (Walsh), and blueberry maggot, Rhagoletis mendax Curran. In 2002 and 2003, larval infestation in blueberries and apples was significantly lower in plots treated with GF-120 (spinosad bait) or SpinTor than in untreated control plots. Fruit fly infestation in apples was reduced by 67% in 2002 after weekly application of GF-120 for 6 wk. Six weeks of GF-120 treatment reduced infestation in blueberries by 85% in 2002 and 98% in 2003. Plots treated weekly with the bait component of GF-120 for 6 wk had significantly higher infestation of blueberry maggot larvae compared with untreated plots in 2002. Observations of wild R. mendax flies revealed that similar numbers of flies landed on blueberry foliage treated with spinosad bait, the bait component alone, or water droplets. However, flies on spinosad bait and bait treated plants spent significantly more time within 5 cm of the treatment droplets compared with control (water) droplets. Overall, the results demonstrate a high degree of efficacy of baited spinosad formulations against these key pests of temperate fruit and suggest that GF-120 is an arrestant for foraging flies.     

Integrated pest management of Rhagoletis mendax (Diptera: Tephritidae) in lowbush blueberry using vegetative field management

Economic control of Rhagoletis mendax was achieved by applying insecticidal sprays to commercial lowbush blueberry vegetative fields, in a biennial production system, rather than to the fruiting fields, when the threshold was exceeded. The viability of this integrated pest management of R. mendax for lowbush blueberries was demonstrated over a 9-yr interval in New Brunswick where three sites were monitored for 2 yr, eight sites for 4 yr, and one site for 9 yr. Control of R. mendax in lowbush blueberry fields was achieved in 2 yr when the fields were isolated, and in 3 yr when there were adjacent lowbush blueberry fields.     

Techniques for monitoring cranberry tipworm (Diptera: Cecidomyiidae) in rabbiteye and southern highbush blueberries

Several monitoring techniques were evaluated for their effectiveness, based on the highest mean captures of cranberry tipworm, Dasineura oxycoccana (Johnson), in detecting D. oxycoccana in rabbiteye, Vaccinium ashei Reade, and southern highbush, V. corymbosum L. x V. darrowi Camp, blueberry plantings. There were no significant differences in captures of D. oxycoccana adults on unbaited sticky board traps, regardless of color (yellow, white, green, or blue). In a separate experiment, three monitoring techniques, yellow unbaited sticky boards, larval/adult emergence from infested buds, and bud dissection, were evaluated for detecting D. oxycoccana, eggs, larvae, and adults. In total, four bud types were examined, including rabbiteye floral, rabbiteye leaf, southern highbush floral, and southern highbush leaf. The emergence monitoring technique detected significantly more D. oxycoccana adults than the other techniques evaluated. Emergence and dissection techniques performed equally well for detecting D. oxycoccana larvae. Dissection was the only technique capable of detecting D. oxycoccana eggs. Overall, the highest numbers of D. oxycoccana eggs were detected in southern highbush leaf buds. However, larval infestation was lower for southern highbush leaf buds compared with other bud types sampled. Hypotheses to explain this phenomenon are discussed. The fewest number of eggs was recorded for southern highbush flower buds, potentially because these buds develop before peak emergence of D. oxycoccana. Managing D. oxycoccana in infested plantings can be improved by incorporating monitoring techniques, specifically bud dissection to search for eggs, that will aid growers in making timely insecticide applications.     

Morphological and molecular characterization of Phomopsis vaccinii and additional isolates of Phomopsis from blueberry and cranberry in the eastern United States

Forty isolates of Phomopsis were obtained from twigs and berries of highbush blueberry, Vaccinium corymbosum, and cranberry, Vaccinium macrocarpon, isolated primarily from plants grown in the eastern United States. They were characterized using conidiomatal morphology, conidial dimensions, colony appearance and growth rate, and sequences of ITS rDNA. Based on morphological and molecular similarities, most isolates grouped together with an authentic culture of Phomopsis vaccinii Shear. This taxon is described and illustrated. However, some Phomopsis isolates from Vaccinium differed in colony and conidiomatal morphology from P. vaccinii and, based on ITS sequences, were related to isolates of Phomopsis from diverse hosts. These isolates were excluded from P. vaccinii.     

Susceptibility of low-chill blueberry cultivars to Mediterranean fruit fly, oriental fruit fly, and melon fly (Diptera: Tephritidae)

No-choice tests were conducted to determine whether fruit of southern highbush blueberry, Vaccinium corymbosum L., hybrids are hosts for three invasive tephritid fruit flies in Hawaii. Fruit of various blueberry cultivars was exposed to gravid female flies of Bactrocera dorsalis Hendel (oriental fruit fly), Ceratitis capitata (Wiedemann) (Mediterranean fruit fly), or Bactrocera cucurbitae Coquillet (melon fly) in screen cages outdoors for 6 h and then held on sand in the laboratory for 2 wk for pupal development and adult emergence. Each of the 15 blueberry cultivars tested were infested by oriental fruit fly and Mediterranean fruit fly, confirming that these fruit flies will oviposit on blueberry fruit and that blueberry is a suitable host for fly development. However, there was significant cultivar variation in susceptibility to fruit fly infestation. For oriental fruit fly, 'Sapphire' fruit produced an average of 1.42 puparia per g, twice as high as that of the next most susceptible cultivar 'Emerald' (0.70 puparia per g). 'Legacy', 'Biloxi', and 'Spring High' were least susceptible to infestation, producing only 0.20-0.25 oriental fruit fly puparia per g of fruit. For Mediterranean fruit fly, 'Blue Crisp' produced 0.50 puparia per g of fruit, whereas 'Sharpblue' produced only 0.03 puparia per g of fruit. Blueberry was a marginal host for melon fly. This information will aid in development of pest management recommendations for blueberry cultivars as planting of low-chill cultivars expands to areas with subtropical and tropical fruit flies. Planting of fruit fly resistant cultivars may result in lower infestation levels and less crop loss.     

Native bees with floral sonication behaviour can achieve high-performance pollination of highbush blueberry in Chile

1. Blueberry is one of the most relevant buzz-pollinated crops worldwide and Chile is the most important global producer of fresh blueberries during wintertime in the Northern Hemisphere. Thousands of exotic Bombus terrestris are imported from Europe to pollinate blueberries. However, no study has investigated the performance of the native Chilean fauna to pollinate blueberry or other crops. Therefore, we aimed to compare the performance of native Chilean floral visitors with managed visitors to pollinate highbush blueberry.
2. Per-visit pollination performance (stigmatic pollen deposition) and floral visitation were measured and the presence of sonication behaviour of flower visitors was evaluated for five cultivars in two blueberry orchards located in southern Chile.
3. Floral visitors showed a preference for one or more blueberry cultivars, instead of visiting all cultivars equally. Floral visits with sonication deposited more conspecific pollen on stigmas than visits without sonication. Some native sonicating bees (Cadeguala and Bombus), especially Cadeguala occidentalis, were efficient pollen vectors of blueberry and better pollinators than honeybees (5.8 times more pollen transferred) similar to that of the managed bee B. terrestris.
4. The results indicate that some Chilean native bee species, especially those with sonication behaviour, can provide pollination service to highbush blueberry crops.

     

Comparison of neonicotinoid insecticides for use with biodegradable and wooden spheres for control of key Rhagoletis species (Diptera: Tephritidae).

Field-based studies and laboratory bioassays were conducted with apple maggot, Rhagoletis pomonella (Walsh), and blueberry maggot, Rhgoletis mendax Curran, flies to investigate the performance and duration of activity of insecticide-treated biodegradable and wooden spheres for control of Rhagoletis species. Four neonicotinoid insecticide treatments including imidacloprid, thiamethoxam, and thiocloprid at 2% (AI) were evaluated with biodegradable spheres. In 1999, significantly more apple maggot flies were found killed by imidacloprid-treated spheres compared with thiamethoxam-treated spheres during early and late season. In 2000, spheres treated with either of two formulations of imidacloprid killed significantly more apple maggot flies compared with thiamethoxam, thiocloprid, and untreated spheres. In blueberries, there were no significant differences between the numbers of blueberry maggot flies killed by both imidacloprid-treated or thiamethoxam-treated spheres in 1999. However, during the 2000 blueberry field season, both formulations of imidacloprid were significantly more effective in killing blueberry maggot flies compared with spheres treated with thiamethoxam, thiocloprid and untreated controls. Overall, spheres treated with thiocloprid were ineffective and did not kill significantly more apple maggot or blueberry maggot flies compared with the controls. Laboratory bioassays showed that the effectiveness of field-exposed spheres treated with imidacloprid at 4 and d 8% (AI) and thiamethoxam at 4% (AI) in killing apple maggot flies was not significantly reduced over a 12-wk aging period. Additionally, wooden spheres aged outdoors for 12 wk with and without mold maintained residual activity in laboratory tests, whereas biodegradable spheres of equal aging, with and without mold lost their effectiveness in killing apple maggot flies. In other studies, we confirmed that the addition of an external feeding stimulant (sucrose) significantly increases the effectiveness of both biodegradable and wooden spheres treated with imidacloprid at 2% (AI).     

Examining the spatial distribution of flower thrips in southern highbush blueberries by utilizing geostatistical methods

Flower thrips (Frankliniella spp.) are one of the key pests of southern highbush blueberries (Vaccinium corymbosum L. x V. darrowii Camp), a high-value crop in Florida. Thrips' feeding and oviposition injury to flowers can result in fruit scarring that renders the fruit unmarketable. Flower thrips often form areas of high population, termed "hot spots", in blueberry plantings. The objective of this study was to model thrips spatial distribution patterns with geostatistical techniques. Semivariogram models were used to determine optimum trap spacing and two commonly used interpolation methods, inverse distance weighting (IDW) and ordinary kriging (OK), were compared for their ability to model thrips spatial patterns. The experimental design consisted of a grid of 100 white sticky traps spaced at 15.24-m and 7.61-m intervals in 2008 and 2009, respectively. Thirty additional traps were placed randomly throughout the sampling area to collect information on distances shorter than the grid spacing. The semivariogram analysis indicated that, in most cases, spacing traps at least 28.8 m apart would result in spatially independent samples. Also, the 7.61-m grid spacing captured more of the thrips spatial variability than the 15.24-m grid spacing. IDW and OK produced maps with similar accuracy in both years, which indicates that thrips spatial distribution patterns, including "hot spots," can be modeled using either interpolation method. Future studies can use this information to determine if the formation of "hot spots" can be predicted using flower density, temperature, and other environmental factors. If so, this development would allow growers to spot treat the "hot spots" rather than their entire field.     

Effect of trap size, placement, and age on captures of blueberry maggot flies (Diptera: Tephritidae)

Ammonium acetate and protein hydrolysate baited and unbaited green spheres (3.6, 9.0, and 15.6 cm diameter) were evaluated for effectiveness in capturing blueberry maggot flies, Rhagoletis mendax Curran. Early in the season, baited spheres (9.0 cm diameter) captured significantly more R. mendax flies than spheres of 3.6 and 15.6 cm diameter. As the season progressed, the differences in trap captures became less pronounced among the 3.6-, 9.0-, and 15.6-cm-diameter spheres. In other experiments, the effects of trap positions and age on captures of blueberry maggot flies were assessed. Traps were positioned 15 cm above the bush canopy, 15 cm inside the canopy (from top of the bush), and 45 cm from the ground. Traps placed within the canopy captured 2.5 and 1.5 times as many flies compared with traps placed above the canopy and 45 cm from the ground, respectively. When sticky yellow Pherocon AM boards and green sphere traps were allowed to age in field cages, freshly baited (0 d) yellow sticky boards captured significantly more blueberry maggot flies than boards aged for 11, 28, and 40 d, respectively. No significant differences were observed among boards aged for 11, 28, and 40 d. However, when baited 9-cm sticky spheres were aged in field cages, there were no significant differences between freshly baited spheres and spheres aged for 11 and 28 d, respectively. Spheres aged for 40 d differed significantly from freshly baited ones. The study demonstrated that the baited 9-cm-diameter sphere was more effective in capturing blueberry maggot flies than spheres of 3.6 and 15.6 cm diameter. When this trap is deployed in the center of the bush canopy approximately 15 cm from the top of the bush, it is attractive and accessible to R. mendax flies. The data also indicated that a baited 9-cm sphere has a longer effective life span than Pherocon AM boards when deployed under the same field conditions.     

Genomic insight into the developmental history of southern highbush blueberry populations

Interspecific hybridization is a common breeding approach for introducing novel traits and genetic diversity to breeding populations. Southern highbush blueberry (SHB) is a blueberry cultivar group that has been intensively bred over the last 60 years. Specifically, it was developed by multiple interspecific crosses between northern highbush blueberry [NHB, Vaccinium corymbosum L. (2n = 4x = 48)] and low-chill Vaccinium species to expand the geographic limits of highbush blueberry production. In this study, we genotyped polyploid blueberries, including 105 SHB, 17 NHB, and 10 rabbiteye blueberry (RE) (Vaccinium virgatum Aiton), from the accessions planted at Poplarville, Mississippi, and accessions distributed in Japan, based on the double-digest restriction site-associated DNA sequencing. The genome-wide SNP data clearly indicated that RE cultivars were genetically distinct from SHB and NHB cultivars, whereas NHB and SHB were genetically indistinguishable. The population structure results appeared to reflect the differences in the allele selection strategies that breeders used for developing germplasm adapted to local climates. The genotype data implied that there are no or very few genomic segments that were commonly introgressed from low-chill Vaccinium species to the SHB genome. Principal component analysis-based outlier detection analysis found a few loci associated with a variable that could partially differentiate NHB and SHB. These SNP loci were detected in Mb-scale haplotype blocks and may be close to the functional genes related to SHB development. Collectively, the data generated in this study suggest a polygenic adaptation of SHB to the southern climate, and may be relevant for future population-scale genome-wide analyses of blueberry.Subject terms: Agricultural genetics, Plant breeding     

Effectiveness of thiamethoxam-coated spheres against blueberry maggot flies (Diptera: Tephritidae)

Studies were conducted to evaluate the mortality of blueberry maggot, Rhagoletis mendax Curran, flies exposed to thiamethoxam- and imidacloprid-coated biodegradable (8-cm-diameter) red spheres, under both laboratory and field conditions. Laboratory studies with spheres coated with 0.1-2.0% (AI) of thiamethoxam indicated that they are effective against R. mendax; however, no dose-dependent response was observed. Studies on the effect of visitation time on thiamethoxam-coated spheres showed a decrease in R. mendax mortality as the duration of visitation time decreased from 60 to 10 s. Under field conditions, significantly more flies were captured on Plexiglas panes below the 2% (AI) thiamethoxam-coated spheres when compared with similar panes below untreated spheres. In field evaluations of thiamethoxam- and imidacloprid-coated spheres, imidacloprid-coated spheres (2.0% [AI]) were found to be significantly more effective than thiamethoxam-coated spheres (0.5-4.0% [AI]). Field trials to characterize the levels of mortality associated with aging pesticide-coated spheres revealed that the effectiveness of treated spheres decreased with increasing age of sphere, and this reduction in effectiveness is greater in thiamethoxam-coated spheres than in imidacloprid-coated spheres. These results provide comparative data on the effectiveness of thiamethoxam- and imidacloprid-coated spheres and support the potential of using pesticide-treated spheres for control of blueberry maggot flies.