Tracking Sweet Potato Leaf Curl Virus through Field Production: Implications for Sustainable Sweetpotato Production and Breeding Practices.

Sweet potato leaf curl virus (SPLCV) is a whitefly-transmitted begomovirus infecting sweetpotato and other morning glory (Convolvulaceae) species worldwide. The virus is widespread at the USDA, ARS, U.S. Vegetable Laboratory (USVL), and testing of germplasm maintained in the breeding program indicates nearly 100% infection in storage roots of materials propagated for at least four years. Prior to the public release of new germplasm, viruses must be eliminated via laborious and time-consuming meristem-tip culture. The identification of virus-free seedlings early in the selection process can offer an alternative to meristem-tip culture. In this study, we investigated the transmission of SPLCV over two years of consecutive field plantings (early and late) of sweetpotato. While SPLCV is endemic at the USVL, virus transmission pressure over the typical cultivation season is unknown, and avoidance of virus transmission paired with the selection and maintenance of clean material may be a viable alternative to virus elimination. In 2022, the storage roots of 39 first-year seedling (FYS) selections were tested for SPLCV after early-season cultivation, revealing a single selection (2.6%) with a positive test. Similar testing was conducted in 2023 with no SPLCV-positive FYS selections detected. To further assess SPLCV acquisition in the field, replicated late-season plantings of each selected FYS (n = 37) were monitored from planting to harvest. Testing was conducted at 60 and 120 days after planting (DAP). Approximately 35% of the bulk samples were infected at 60 DAP, and infection increased to 52.3% by 120 DAP. Testing of individuals within selected positive bulked samples did not support 100% infection at harvest. Altogether, these results demonstrate that SPLCV transmission during early planting is sufficiently low to facilitate the maintenance of virus-free selections, offering an alternative to virus cleaning and a cultivation strategy that may be leveraged for production.

Mitochondrial genome datasets for the sweetpotato weevil, Cylas formicarius elegantulus (Coleoptera: Brentidae), collected in the United States.

The sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), is one of the most destructive pests of sweetpotato worldwide. Genomic analyses of sweetpotato weevils can provide insights into their genetic diversity, population structure, and dispersal as well as provide information to support management strategies. Adult sweetpotato weevils were collected by various methods from Ipomoea batatas L. (sweetpotato) or I. coccinea L. (red morning glory) in the U.S. states of Georgia, Hawaii, South Carolina, and Texas. Genomic DNA was extracted from individual weevil specimens and sequenced using Illumina NovaSeq. A total of 181 GB of 150 base pair (bp) paired-end reads were generated for 40 specimens. Mitochondrial genomes were assembled for each specimen via reference mapping and annotated using Geneious Prime. Full mitochondrial genome sequences range from 17,141 to 17,152 bp with an average GC content of 21.8% and average coverage of 3307 × . A maximum likelihood phylogenetic analysis considering the mitochondrial protein coding genes is provided. Mitochondrial genomes and assembled reads are deposited in NCBI GenBank, providing 40 mitogenomes of C. formicarius elegantulus collected in the U.S.

Genome Sequences of Novel Iflaviruses in the Gray Lawn Leafhopper, an Experimental Vector of Corn Stunt Spiroplasma.

Two novel iflaviruses were detected in the metatranscriptome of the gray lawn leafhopper, Exitianus exitiosus (Uhler). The assembled genome sequence of Exitianus exitiosus virus 1 was 9,858 nucleotides (nt) long and encodes a 3,083-amino acid (aa) polyprotein. Exitianus exitiosus virus 2 was 10,219 nt long and encodes a 2,947-aa polyprotein.

Large-Scale Seedling Grow-Out Experiments Do Not Support Seed Transmission of Sweet Potato Leaf Curl Virus in Sweet Potato.

Sweet potato leaf curl virus (SPLCV) threatens global sweet potato production. SPLCV is transmitted by Bemisia tabaci or via infected vegetative planting materials; however, SPLCV was suggested to be seed transmissible, which is a characteristic that is disputed for geminiviruses. The objective of this study was to revisit the validity of seed transmission of SPLCV in sweet potato. Using large-scale grow-out of sweet potato seedlings from SPLCV-contaminated seeds over 4 consecutive years, approximately 23,034 sweet potato seedlings of 118 genotype entries were evaluated. All seedlings germinating in a greenhouse under insect-proof conditions or in a growth chamber were free of SPLCV; however, a few seedlings grown in an open bench greenhouse lacking insect exclusion tested positive for SPLCV. Inspection of these seedlings revealed that B. tabaci had infiltrated the greenhouse. Therefore, transmission experiments were conducted using B. tabaci MEAM1, demonstrating successful vector transmission of SPLCV to sweet potato. Additionally, tests on contaminated seed coats and germinating cotyledons demonstrated that SPLCV contaminated a high percentage of seed coats collected from infected maternal plants, but SPLCV was never detected in emerging cotyledons. Based on the results of grow-out experiments, seed coat and cotyledon tests, and vector transmission experiments, we conclude that SPLCV is not seed transmitted in sweet potato.

Whitefly Endosymbionts: Biology, Evolution, and Plant Virus Interactions.

Whiteflies (Hemiptera: Aleyrodidae) are sap-feeding global agricultural pests. These piercing-sucking insects have coevolved with intracellular endosymbiotic bacteria that help to supplement their nutrient-poor plant sap diets with essential amino acids and carotenoids. These obligate, primary endosymbionts have been incorporated into specialized organs called bacteriomes where they sometimes coexist with facultative, secondary endosymbionts. All whitefly species harbor the primary endosymbiont Candidatus Portiera aleyrodidarum and have a variable number of secondary endosymbionts. The secondary endosymbiont complement harbored by the cryptic whitefly species Bemisia tabaci is particularly complex with various assemblages of seven different genera identified to date. In this review, we discuss whitefly associated primary and secondary endosymbionts. We focus on those associated with the notorious B. tabaci species complex with emphasis on their biological characteristics and diversity. We also discuss their interactions with phytopathogenic begomoviruses (family Geminiviridae), which are transmitted exclusively by B. tabaci in a persistent-circulative manner. Unraveling the complex interactions of these endosymbionts with their insect hosts and plant viruses could lead to advancements in whitefly and whitefly transmitted virus management.

Debugging: Strategies and Considerations for Efficient RNAi-Mediated Control of the Whitefly Bemisia tabaci.

The whitefly Bemisia tabaci is a globally important pest that is difficult to control through insecticides, transgenic crops, and natural enemies. Post-transcriptional gene silencing through RNA interference (RNAi) has shown potential as a pest management strategy against B. tabaci. While genomic data and other resources are available to create highly effective customizable pest management strategies with RNAi, current applications do not capitalize on species-specific biology. This lack of specificity has the potential to have substantial ecological impacts. Here, we discuss both short- and long-term considerations for sustainable RNAi pest management strategies for B. tabaci, focusing on the need for species specificity incorporating both life history and population genetic considerations. We provide a conceptual framework for selecting sublethal target genes based on their involvement in physiological pathways, which has the greatest potential to ameliorate unintended negative consequences. We suggest that these considerations allow an integrated pest management approach, with fewer negative ecological impacts and reduced likelihood of the evolution of resistant populations.

Exploring the Use of High-Resolution Melting Analysis and Helicase-Dependent Amplification for Discrimination of Bemisia tabaci (Hemiptera: Aleyrodidae) Cryptic Species and Trialeurodes vaporariorum.

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera; Aleyrodidae), and greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae), are highly problematic plant pests and virus vectors with worldwide distributions. Identification of whitefly species is typically accomplished by observation of distinct morphological characters; however, because of morphological inconsistency and indistinguishability, the discrimination of B. tabaci species variants is dependent on molecular techniques based on genetic differences. New assays were designed for the detection of B. tabaci A, B, and Q mitotype groups, and T. vaporariorum. Specific primer sets were designed for amplification of the mitochondrial cytochrome c oxidase I gene of the four targets to perform in end-point PCR, real-time PCR coupled to high-resolution melting analysis (HRM), and the isothermal helicase-dependent amplification (HDA). Primer specificities were validated using end-point PCR, then tested in HRM and HDA. Bemisia tabaci A, B, and Q mitotypes, and T. vaporariorum-targeted primer sets discriminately amplified specimens of different populations within their target whitefly group. These tests provide three novel discrimination assays for the high-consequence, exotic B. tabaci B and Q groups, along with the native B. tabaci A group and T. vaporariorum.

On the origin of Anagyrus callidus (Hymenoptera: Encyrtidae), a parasitoid of pink hibiscus mealybug Maconellicoccus hirsutus (Hemiptera: Pseudococcidae).

Anagyrus callidus Triapitsyn, Andreason Perring (Hymenoptera: Encyrtidae), recently described from southern California, USA and Mexico, is a primary parasitoid of the pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae). This wasp species previously was misidentified as Anagyrus kamali Moursi, which was introduced and released as such in the United States (California and Florida) and Mexico. In this paper, the origin of A. callidus is shown to be from Taiwan, based on differences in the morphology and molecular sequences of voucher specimens of an earlier colony of the misidentified A. kamali from Puerto Rico (released in August 2002 in southern Florida), and specimens that originated in southern Taiwan.

Lethal and Sub-Lethal Effects of Insecticides on the Pink Hibiscus Mealybug, Maconellicoccus hirsutus (Hemiptera: Pseudococcidae).

The pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a pest of many plants, and a new problem on dates in California. The effects of seven insecticides and water on different life stages of this mealybug were studied to identify the best material for control. Water did not have any significant effect on mealybugs, but the insecticide treatments significantly affected all life stages tested. The egg hatch rate ranged from 28.5% to 17.2% for spirotetramat, bifenthrin, flupyradifurone, fenpropathrin, and buprofezin treatments, and was lower for sulfoxaflor (2.8%) and acetamiprid (0.1%). Despite high survival of neonate crawlers in the non-treated control and water treatments, 53.1% and 34.6% survived in the spirotetramat and buprofezin treatments, respectively; survival was zero in the other treatments. Spirotetramat and buprofezin caused very low mortality of nymphs in the first day post-treatment, but mortality significantly increased over time and reached 42.8% and 50.6% by day 6, respectively. The other treatments were highly toxic to the nymphs (79.4⁻99.4% on day 6). Insecticides also had a significant effect on the feeding ability of nymphs. By day 6 after treatment, 73.9% to 100% of nymphs treated with different insecticides stopped feeding although they were still alive. Insecticides showed no effect on the mortality of adult females, but the percentages of ovipositing females were significantly reduced (51.1% to 10.6%) in all insecticide treatments, except buprofezin, which was not statistically different from water and the non-treated control. In the process of our studies, we identified abnormalities in the appearance of eggs from females treated with various insecticides, and these aberrant eggs are described.

Reduced Susceptibility of Homalodisca vitripennis (Hemiptera: Cicadellidae) to Commonly Applied Insecticides.

Pest management for the glassy-winged sharpshooter, Homalodisca vitripennis Germar (Hemiptera: Cicadellidae), in Kern County, California relies on the application of insecticides. These treatments have contributed to low H. vitripennis field counts since applications were initiated in 2001. However, densities have been high in recent years despite continued management, prompting efforts to evaluate the susceptibility of current populations to insecticides. H. vitripennis adults were subjected to bioassays with five commonly applied insecticides, and the results were compared to baseline toxicities determined in 2002. Two neonicotinoids, imidacloprid and thiamethoxam, were evaluated using systemic uptake bioassays. Contact toxicities of the neonicotinoid acetamiprid and pyrethroids bifenthrin and fenpropathrin were estimated using leaf dip bioassays. Dose-mortality responses were analyzed by probit analysis. For each compound, there was no significant difference in annual LC50 values determined over 2 yr. Compared to baseline toxicities, acetamiprid and bifenthrin were found to be significantly less toxic to H. vitripennis. The LC50 values of these two compounds increased sevenfold and 152-fold, respectively. Tests with the neonicotinoids revealed a trend of decreasing susceptibility levels within each season followed by reversion back to early season LC50 estimates in the following year. In addition, data showed seasonal and site variation in susceptibility to imidacloprid, possibly due to differential applications in nearby fields.

Single-Target and Multiplex Discrimination of Whiteflies (Hemiptera: Aleyrodidae) Bemisia tabaci and Trialeurodes vaporariorum With Modified Priming Oligonucleotide Thermodynamics.

The whitefly species Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) are worldwide agricultural pests and virus vectors. Bemisia tabaci, in particular, is often transported internationally via trade routes leading to potential introductions of exotic whiteflies or plant viruses. Quick identification of agriculturally important whiteflies can facilitate interventions that prevent these cross-border introductions. Polymerase chain reaction (PCR) primers were designed to amplify the mitochondrial cytochrome oxidase I gene (mtCOI) sequence of members of the B. tabaci complex, MEAM1, MED, and NW, and T. vaporariorum. Primers incorporated an A/T-rich overhang sequence at the 5' terminus (5' flap) to test for increased primer sensitivity and assay efficiency. Single-target and multiplex endpoint PCR assays with the eight primer sets were performed using genomic DNA template extracted from individual adult whiteflies. Resultant PCR amplicons obtained for B. tabaci MEAM1, MED, and NW, and T. vaporariorum primers with the 5' flap were 559-, 717-, 353-, and 258-bp, respectively, and without the 5' flap were 550-, 712-, 329-, and 252-bp in length, respectively. In single-target and multiplex reactions, specific amplification was achieved using both the unmodified and 5' flap-modified primers. Sequencing and phylogenetic analysis confirmed primer-target amplification specificity. Using these primer sets in single-target or multiplex PCR allows for quick discrimination and specific identification of B. tabaci complex members and T. vaporariorum, and the addition of 5'A/T-rich overhang sequences increases the sensitivity and amplification of some primer sets.