Preference and performance of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae) on strawberry cultivars

Phased gap-free genome assembly of octoploid cultivated strawberry illustrates the genetic and epigenetic divergence among subgenomes

The genetic and epigenetic mechanisms underlying the coexistence and coordination of the four diverged subgenomes (ABCD) in octoploid strawberries (Fragaria × ananassa) remains poorly understood. In this study, we have assembled a haplotype-phased gap-free octoploid genome for the strawberry, which allowed us to uncover the sequence, structure, and epigenetic divergences among the subgenomes. The diploid progenitors of the octoploid strawberry, apart from subgenome A (Fragaria vesca), have been a subject of public controversy. Phylogenomic analyses revealed a close relationship between diploid species Fragaria iinumae and subgenomes B, C, and D. Subgenome A, closely related to F. vesca, retains the highest number of genes, exhibits the lowest content of transposable elements (TEs), experiences the strongest purifying selection, shows the lowest DNA methylation levels, and displays the highest expression level compared to the other three subgenomes. Transcriptome and DNA methylome analyses revealed that subgenome A-biased genes were enriched in fruit development biological processes. In contrast, although subgenomes B, C, and D contain equivalent amounts of repetitive sequences, they exhibit diverged methylation levels, particularly for TEs located near genes. Taken together, our findings provide valuable insights into the evolutionary patterns of subgenome structure, divergence and epigenetic dynamics in octoploid strawberries, which could be utilized in strawberry genetics and breeding research.

A high-throughput KASP assay provides insights into the evolution of multiple resistant mutations in populations of the two-spotted spider mite Tetranychus urticae across China

BACKGROUND

The two-spotted spider mite (TSSM), Tetranychus urticae (Acari: Tetranychidae), is a cosmopolitan phytophagous pest in agriculture and horticulture. It has developed resistance to many acaricides by target-site mutations. Understanding the status and evolution of resistant mutations in the field is essential for resistance management. Here, we applied a high-throughput Kompetitive allele-specific polymerase chain reaction (KASP) method for detecting six mutations conferring resistance to four acaricides of the TSSM. We genotyped 3274 female adults of TSSM from 43 populations collected across China in 2017, 2020, and 2021.

RESULTS

The KASP genotyping of 24 testing individuals showed 99% agreement with Sanger sequencing results. KASP assays showed that most populations had a high frequency of mutations conferring avermectin (G314D and G326E) and pyridaben (H92R) resistance. The frequency of mutation conferring bifenazate (A269V and G126S) and etoxazole (I1017F) resistance was relatively low. Multiple mutations were common in the TSSM, with 70.2% and 24.6% of individuals having 2-6 and 7-10 of 10 possible resistant alleles, respectively. No loci were linked in most populations among the six mutations, indicating the development of multiple resistance is mainly by independent selection. However, G314D and I1017F on the nuclear genome deviated from Hardy-Weinberg equilibrium in most populations, indicating significant selective pressure on TSSM populations by acaricides or fitness cost of the mutations in the absence of acaricide selection.

CONCLUSION

Our study revealed that the high frequency of TSSMs evolved multiple resistant mutations in population and individual levels by independent selection across China, alarming for managing multiple-acaricides resistance. © 2023 Society of Chemical Industry.

Population Dynamics of Heliothrips haemorrhoidalis (Thysanoptera: Thripidae) in Strawberry Cultivars in Southern Brazil

Heliothrips haemorrhoidalis is a polyphagous thrips species that has been reported as a potential pest in strawberry cultivation in Brazil. Since it has only recently emerged as a pest species in production areas, understanding seasonal trends in the species' activity is particularly important for designing management strategies. Therefore, this study aims to investigate the influence of climate factors (temperature and relative humidity) and six strawberry cultivars ('Albion', 'Aromas', 'Camino Real', 'Monterey', 'Portola', and 'San Andreas') on the population dynamics of H. haemorrhoidalis during the 2018-2019 and 2019-2020 growing seasons in southern Brazil. The greatest peak in thrips populations in the cultivars assessed occurred between January and March (summer) in both growing seasons. The relationship between the incidence of H. haemorrhoidalis and temperature was observed to be negative during the autumn, spring, and summer months but positive during winter. Relative humidity levels above 70% had a negative influence on the abundance of insects. Populations of H. haemorrhoidalis varied between the cultivars as follows: 'Aromas' > 'Monterey' > 'San Andreas' > 'Albion' > 'Camino Real' > 'Portola'. Cross-sections of strawberry leaves showed that 'Monterey' had the highest density of nonglandular trichomes/mm2 (7.26), while 'Portola' cultivar, the greatest predominance of glandular trichomes/mm2 (12.67), which may have contributed to the incidence of H. haemorrhoidalis. The demographic information presented on H. haemorrhoidalis in strawberry cultivars provides a starting point to better understand the insect's population dynamics. These results also indicate that climatic conditions are a limiting factor for the development of H. haemorrhoidalis.

Acarofauna present in organic strawberry fields and associated weed species in southern Brazil

The presence of weeds in the margins of strawberry crops can enhance populations of predatory mites as a measure to support conservation biological control. The aims of this study were (i) to assess the composition of the acarofauna associated with strawberries and the accompanying herbaceous plants in an organic farming system, and (ii) to evaluate the possible relationships between phytophagous and predatory mites occurring in this system. Strawberry leaves and whole plants of weeds were sampled biweekly from August 2014 to February 2015 in Lapa (Paraná, Brazil). In total, 23 weed species belonging to 10 families were identified; 3768 mite individuals (from 15 families and 4 suborders) were recovered, 77% on strawberries and 23% on weeds. Abundance of predatory mites on weeds was greater than on strawberry cultivars. On strawberries, the most abundant family was Tetranychidae (84%) followed by Phytoseiidae (11.6%). In total, 16 predatory mite species from the Phytoseiidae family were identified, 13 of them occurring on strawberry leaflets. Typholodromalus aripo, Neoseiulus californicus and Typhlodromips mangleae were the most abundant mite species on strawberry leaves. On weeds, most individuals were predatory mites (59%), whereas phytophagous mites represented 17.2%. The most abundant family was Phytoseiidae (36.4%). On weeds, the phytoseiid mite T. aripo was the most abundant species, representing 34.7%. Besides being found on strawberry leaflets, T. aripo was associated with 15 weed species. Among the weeds, Bidens pilosa showed the highest values of the Shannon index (1.97), Margalef index (3.04), and Pielou's evenness index (0.95). This study emphasizes the importance of surrounding weeds as a shelter for beneficial mitefauna in strawberry fields, likely contributing to enhance conservation biological control.

Performance of Tetranychus urticae (Acari: Tetranychidae) on three hop cultivars (Humulus lupulus)

Tetranychus urticae Koch (Acari: Tetranychidae) is a major pest species in numerous crops including hop (Humulus lupulus L.). Substantial T. urticae infestation was observed to occur in this recently introduced crop in Brazil. The adoption of less suitable cultivars to the pest species is highly desirable for integrated pest management. We used free-choice trials and two-sex life table analysis to determine the preference and population growth of T. urticae under laboratory conditions using three of hop cultivars currently expanding in Brazil (Mantiqueira, Victoria, and Yakima Gold). We also estimated the density of non-glandular trichomes and lupulin glands found on the abaxial leaf surface of these cultivars and correlated them with performance parameters of T. urticae. Mantiqueira appeared to be the least preferred by adult females for attractiveness and oviposition suggesting existence of antixenosis on this cultivar. Female immature stages developed slower on Yakima Gold and Mantiqueira, but no difference was observed between the latter and Victoria. Fecundity and longevity were significantly lower on Mantiqueira than on Victoria and Yakima Gold. No significant differences were observed among cultivars for intrinsic rate of increase (r), finite rate of increase (λ), and net rate of reproduction (R₀), suggesting the absence of antibiosis. Although, lupilin gland densities were higher on Mantiqueira and Yakima Gold than on Victoria, no significant correlations were observed between these defensive traits and performance parameters of T. urticae. However, 30-day population simulations of T. urticae suggest that Yakima Gold is the least susceptible, Mantiqueira is moderately susceptible, and Victoria is highly susceptible.

Catch me if you can: the influence of refuge / trap design, previous feeding experience, and semiochemical lures on vine weevil (Coleoptera: Curculionidae) monitoring success

BACKGROUND

Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is one of the most economically important pest species of berry and ornamental crops globally. Monitoring this nocturnal pest can be difficult and time consuming and the efficacy of current tools is uncertain. Without effective monitoring tools, implementation of integrated pest management strategies is challenging. This study tests the relative efficacy of a range of vine weevil monitoring tools. Whether host-plant volatiles and weevil feeding experience influence vine weevil capture is also tested.

RESULTS

Monitoring tool efficacy differed overall between the six monitoring tool designs tested and ranged from catches of 0.4% to 26.7% under semi-field conditions. Previous feeding experience influenced vine weevil behavior. In yew conditioned populations, 39% of the weevils responded to and were retained in the trap baited with yew foliage while 37% of weevils from Euonymus fortunei conditioned populations responded to and were retained in the trap baited with E. forunei foliage. A simple synthetic lure consisting of (Z)-2-pentenol + methyl eugenol also increased vine weevil catches compared with an unbaited trap.

CONCLUSION

Demonstrating differences in the efficacy of different monitoring tool designs is an important first step for developing improved methods for monitoring vine weevil populations within crops. This study presents the first direct comparison of vine weevil monitoring tool designs and indicates that trap efficacy can be improved by baiting with host-plant material or a synthetic lure based on host-plant volatiles. © 2019 Society of Chemical Industry.

Transcriptomic and proteomic response of Manihot esculenta to Tetranychus urticae infestation at different densities

Tetranychus urticae (Acari: Tetranychidae) is an extremely serious cassava (Manihot esculenta) pest. Building a genomic resource to investigate the molecular mechanisms of cassava responses to T. urticae is vital for characterizing cassava resistance to mites. Based on the tolerance of cassava varieties to mite infestation (focusing on mite development rate, fecundity and physiology), cassava variety SC8 was selected to analyze transcriptomic and proteomic changes after 5 days of T. urticae feeding. Transcriptomic analysis revealed 698 and 2140 genes with significant expression changes under low and high mite infestation, respectively. More defense-related genes were found in the enrichment pathways at high mite density than at low density. In addition, iTRAQ-labeled proteomic analysis revealed 191 proteins with significant expression changes under low mite infestation. Differentially expressed genes and proteins were mainly found in the following defense-related pathways: flavonoid biosynthesis, phenylpropanoid biosynthesis, and glutathione metabolism under low-density mite feeding and plant hormone signal transduction and plant-pathogen interaction pathways under high-density mite feeding. The plant hormone signal transduction network, involving ethylene, jasmonic acid, and salicylic acid transduction pathways, was explored in relation to the M. esculenta response to T. urticae. Correlation analysis of the transcriptome and proteome generated a Pearson correlation coefficients of R = 0.2953 (P < 0.01), which might have been due to post-transcriptional or post-translational regulation resulting in many genes being inconsistently expressed at both the transcript and protein levels. In summary, the M. esculenta transcriptome and proteome changed in response to T. urticae, providing insight into the general activation of plant defense pathways in response to mite infestation.

Peanut cultivars display susceptibility by triggering outbreaks of Tetranychus ogmophallos (Acari: Tetranychidae)

The peanut red spider mite, Tetranychus ogmophallos Ferreira and Flechtmann (Acari: Tetranychidae), is an important pest of peanut in Brazil and is considered a quarantine pest in other countries. This study investigates the development, reproduction, survival and life table parameters of T. ogmophallos on five peanut cultivars-three with high levels of oleic acid [high oleic] and recently released: Granoleico, IAC OL 3 and IAC 503; and two regular and previously used by farmers: Runner IAC 886, IAC Tatu ST 3-and two breeding lines (L. 8008 and L. 322) in the growth chamber. There were differences between the developmental times of all immature stages, the oviposition period, fecundity and adult longevity of T. ogmophallos reared on the peanut cultivars and breeding lines. The longest duration of the immature stage and lowest fecundity occurred on cultivars Granoleico and Runner IAC 886, and breeding line L. 322, which also displayed the lowest intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R₀) and the shortest mean generation time (T). The highest fitness occurred on the IAC Tatu ST, IAC OL 3, IAC 503 and L. 8008. Our study shows that peanut cultivars belonging to the group with high oleic trait and recently released (IAC OL 3 and IAC 503) are susceptible to T. ogmophallos, except Granoleico, which is resistant. The regular and previously used cultivar Runner IAC 886 and breeding line L. 322 are resistant to the peanut red spider mite.