Spider-mite problems and control in Taiwan

A multiplex direct PCR method for the rapid and accurate discrimination of three species of spider mites (Acari: Tetranychidae) in fruit orchards in Beijing

Spider mites (Acari: Tetranychidae) are polyphagous pests of economic importance in agriculture, among which the two-spotted spider mite Tetranychus urticae Koch has spread widely worldwide as an invasive species, posing a serious threat to fruit tree production in China, including Beijing. The hawthorn spider mite, Amphitetranychus viennensis Zacher, is also a worldwide pest of fruit trees and woody ornamental plants. The cassava mite, Tetranychus truncatus Ehara, is mainly found in Asian countries, including China, Korea and Japan, and mainly affects fruit trees and agricultural crops. These three species of spider mites are widespread and serious fruit tree pests in Beijing. Rapid and accurate identification of spider mites is essential for effective pest and plant quarantine in Beijing orchard fields. The identification of spider mite species is difficult due to their limited morphological characteristics. Although the identification of insect and mite species based on PCR and real-time polymerase chain reaction TaqMan is becoming increasingly common, DNA extraction is difficult, expensive and time-consuming due to the minute size of spider mites. Therefore, the objective of this study was to establish a direct multiplex PCR method for the simultaneous identification of three common species of spider mites in orchards, A. viennensis, T. truncatus and T. urticae, to provide technical support for the differentiation of spider mite species and phytosanitary measures in orchards in Beijing. Based on the mitochondrial cytochrome c oxidase subunit I (COI) of the two-spotted spider mite and the cassava mite and the 18S gene sequence of the hawthorn spider mite as the amplification target, three pairs of specific primers were designed, and the primer concentrations were optimized to establish a direct multiplex PCR system for the rapid and accurate discrimination of the three spider mites without the need for DNA extraction and purification. The method showed a high sensitivity of 0.047 ng for T. truncatus and T. urticae DNA and 0.0002 ng for A. viennensis. This method eliminates the DNA extraction and sequencing procedures of spider mite samples, offers a possibility for rapid monitoring of multiple spider mites in an integrated microarray laboratory system, reducing the time and cost of leaf mite identification and quarantine monitoring in the field.

Phylogenetic-Related Divergence in Perceiving Suitable Host Plants among Five Spider Mites Species (Acari: Tetranychidae)

Spider mites belonging to the genus Tetranychus infest many important agricultural crops in both fields and greenhouses worldwide and are diversified in their host plant range. How spider mites perceive their suitable host plants remains not completely clear. Here, through two-host-choice designs (bean vs. tomato, and bean vs. eggplant), we tested the efficacies of the olfactory and gustatory systems of five spider mite species (T. urticae, T. truncatus, T. pueraricola, T. piercei, and T. evansi), which differ in host plant range in sensing their suitable host plant, by Y-tube olfactometer and two-choice disc experiments. We found that spider mites cannot locate their suitable host plants by volatile odours from a long distance, but they can use olfactory sensation in combination with gustatory sensation to select suitable host plants at a short distance. Highly polyphagous species displayed strong sensitivity in sensing suitable host plants rather than the lowered sensitivity we expected. Intriguingly, our principal component analyses (PCAs) showed that the similarity among five spider mite species in the performance of perceiving suitable host plants was highly correlated with their relative phylogenetic relationships, suggesting a close relationship between the chemosensing system and the speciation of spider mites. Our results highlight the necessity of further work on the chemosensing system in relation to host plant range and speciation of spider mites.

Evaluating the Potential of Protected Cultivation for Off-Season Leafy Vegetable Production: Prospects for Crop Productivity and Nutritional Improvement

The effects of different protective structures on horticultural and nutritional yield of amaranth and water spinach were studied in three seasons of 2020–2021 in Taiwan. The number of people that can receive recommended dietary intake of iron and β-Carotene from vegetables grown under different production conditions was also estimated. The yield of white and red amaranths was consistently better (7.68–19.70 t/ha) under pink poly-net house in all the seasons, but the yield of water spinach was consistently better under white poly-net house (16.25–20.88 t/ha). Spider mite (fall & spring) and aphid (winter) infestation was mostly observed on all crops under poly-net houses. Neoxanthin, lutein and β-carotene were almost two-fold higher in red amaranth harvested from poly-net houses than open field. Based on the RDI values, β-Carotene supply to both men and women (14+) was consistently higher in all crops produced under pink ploy-net houses in all seasons, except for white amaranth produced under white poly-net house during winter. Its supply to 64,788 more men and 83,298 more women was estimated for red amaranth harvested from pink poly-net house than other production conditions. α-carotene was 2–3 fold higher in amaranths and water spinach harvested from poly-net houses than open field. The iron content of the amaranths was lower in poly-net houses (234.50–574.04 g/ha) than open field (645.42–881.67 g/ha) in the fall, but its supply from pink poly-net house was comparable with open field in the winter. However, pink poly-net house was the highest iron supplier from water spinach (323.90 g/ha) in the winter, which was estimated to provide iron to 19,450–22,939 more men and women than other production conditions. Both poly-net houses were the sole supplier of iron through amaranths in the spring, with pink poly-net house supplying iron to 2,000–5,000 more men and women. Thus, protected cultivation not only leads to more marketable yields but also results in higher quantities of health promoting nutrients. Hence, pink poly-net house may be considered to produce more nutritious vegetables, especially during the off-season to bridge the gaps in the seasonal variations in vegetable consumption, besides providing better income opportunities to the smallholder farmers.

Acaricides of Natural Origin. Part 2. Review of the Literature (2002–2006)

Acari are responsible for millions of dollars worth of damage each year as a result of infestations of animals, plants and man. They directly affect our health and prosperity as animal and plant parasites, vectors of disease, and producers of allergens. The indiscriminate use of pesticides has quickly induced resistance in many parasites. At present, the control of acarid parasitic diseases in agriculture, human and veterinary medicine is mainly based on the use of drugs; and for this reason the lack of effective drugs often prevents the control of some parasitic diseases, making them more serious and important. The use of commercial drugs involves many problems, besides the drug-resistance shown by the most important parasites. Environmental damage and the toxicity of many synthetic drugs, represent the main problems that strongly limit drug use. In addition, drug residues in plant and animal food products are important reasons for further economic losses for farmers and must be regarded as potentially hazardous to man and the environment. Plant-derived compounds are generally more easily degradable and could show a smaller negative environmental impact with respect to synthetic drugs. For these reasons, the evaluation of the antiacarid activity of plant extracts is increasingly being investigated in order to obtain new leads, as demonstrated by recent studies that have evaluated and confirmed the effectiveness of many plant compounds on bacteria, fungi, protozoa, helminths and arthropods. This review will be limited to the class Arachnida, sub-class Acaridi, particularly to their control in agriculture, veterinary and human medicine using natural methods.

Encapsulation of Satureja hortensis L. (Lamiaceae) in chitosan/TPP nanoparticles with enhanced acaricide activity against Tetranychus urticae Koch (Acari: Tetranychidae)

The objective of this study was the fabrication of encapsulated Satureja hortensis essential oil (S.EO) in chitosan/tripolyphosphate nanoparticles (CS/TPP-NPs) via ionic gelation technique and investigation of its acaricidal effect. A high encapsulation efficiency of 96.17% was obtained, which shows successful encapsulation of EOs in CS-TPP nanoparticles. Transmission electron microscopy (TEM) analysis proved the formation of spherical S. hortensis EO-loaded chitosan nanoparticles (S.EO@NPs). Fourier-transform infrared spectroscopy (FTIR) analysis demonstrated the presence of encapsulated S.EO in CS/TPP nanoparticles. The average size of nanoparticles was found to be 192.1 ± 11 nm using dynamic light scattering (DLS) technique. Moreover, durability and fumigant acaricide activity of S.EO@NPs against Tetranychus urticae Koch were investigated. The obtained results demonstrated that there were considerable differences between pure S. hortensis EO and S.EO@NPs in their ovicidal, adulticidal, and persistence activities against T. urticae. The LC₅₀ values of pure EO and as-prepared S.EO@NPs against adult mite were 4.95, 46.98 µL/L after 24 h exposure and 2.02, 31.30 µL/L after 72 h exposure, respectively. Fumigation exposure for 24 and 72 h showed that the sensitivity of adults T. urticae were more than the eggs of T. urticae. The LC₅₀ values of fumigant toxicity of pure S.EO and S.EO@NPs against eggs of T. urticae were measured after 24 and 72 h. The experimental results for 24 h treatment showed 6.71 and 211.66 µL/L air LC₅₀ values for pure S.EO and S.EO@NPs, respectively. In the case of 72 h exposure, The LC₅₀ values of pure S.EO and S.EO@NPs were 4.15 and 107.38 µL/L air, respectively. A sustained release of S.EO from S.EO@NPs was observed during 25 days of the study, indicating the persistence acaricide activity for a long time. The as-prepared S.EO@NPs and pure S.EO illustrated 67% and 2% mortality at 18th day exposure, respectively. The notable increasing of the residual fumigant toxicity may be related to the slow and sustainable release of the active ingredient of EO. Based on this study, the S.EO@NPs showed significantly residual adulticidal activity against adults of T. urticae. S.EO@NPs would be recommended as an alternative for pure EOs and other common acaricides.

Tetranychus urticae (Acari: Tetranychidae) transmits Acidovorax citrulli, causal agent of bacterial fruit blotch of watermelon

The two-spotted spider mite (TSSM) Tetranychus urticae is one of the most important pests of cucurbit plants. If TSSM can act as vector for Acidovorax citrulli (Acc), causal agent of bacterial fruit blotch (BFB), then the movement of mites from infected to healthy plants may represent a potential source of inocula for BFB outbreaks. To confirm the association between Acc and TSSM, we generated a green fluorescent protein-tagged mutant strain (Acc02rf) by transposon mutagenesis and demonstrated that TSSM can transmit Acc from infected to non-infected watermelon plants. Challenge with 10 TSSMs carrying Acc02rf population densities of 1.3 × 10(3) CFU each on freshly grown individual watermelon plants caused disease transmission to 53 %. Incubation periods ranged 7-9 days. Bacteria recovered from symptoms typical of those associated with leaf necrosis were characterized and identified as Acc. To our knowledge, this is the first report showing that TSSM can be a vector of Acc. The results reported here support that the strong association of TSSM with Acc is of particular importance in controlling BFB.

Molecular Effects of Irradiation (Cobalt-60) on the Control of Panonychus citri (Acari: Tetranychidae)

The effective dose of irradiation to control pest mites in quarantine has been studied extensively, but the molecular mechanisms underlying the effects of the irradiation on mites are largely unknown. In this study, exposure to 400 Gy of γ rays had significant (p < 0.05) effects on the adult survival, fecundity and egg viability of Panonychus citri. The irradiation caused the degradation of the DNA of P. citri adults and damaged the plasma membrane system of the egg, which led to condensed nucleoli and gathered yolk. Additionally, the transcriptomes and gene expression profiles between irradiated and non-irradiated mites were compared, and three digital gene expression libraries were assembled and analyzed. The differentially expressed genes were putatively involved in apoptosis, cell death and the cell cycle. Finally, the expression profiles of some related genes were studied using quantitative real-time PCR. Our study provides valuable information on the changes in the transcriptome of irradiated P. citri, which will facilitate a better understanding of the molecular mechanisms that cause the sterility induced by irradiation.

Suspension of Egg Hatching Caused by High Humidity and Submergence in Spider Mites

We tested the effects of high humidity and submergence on egg hatching of spider mites. In both the high humidity and submergence treatments, many Tetranychus and Panonychus eggs did not hatch until after the hatching peak of the lower humidity or unsubmerged controls. However, after humidity decreased or water was drained, many eggs hatched within 1-3 h. This was observed regardless of when high humidity or submergence treatments were implemented: either immediately after oviposition or immediately before hatching was due. Normal eyespot formation was observed in most eggs in the high humidity and submergence treatments, which indicates that spider mite embryos develop even when eggs are underwater. Therefore, delays in hatching are not caused by delayed embryonic development. A delay in hatching was always observed in Panonychus citri (McGregor) but was more variable in Tetranychus urticae Koch and Tetranychus kanzawai Kishida. The high humidity and submergence treatments affected but did not suppress larval development in these species. In contrast, many Oligonychus eggs died following the high humidity treatments. In Tetranychus and Panonychus spider mites, suspension of egg hatching may mitigate the adverse effects of rainfall.

The red spider mite, Oligonychus coffeae (Acari: Tetranychidae): its status, biology, ecology and management in tea plantations

Oligonychus coffeae Nietner (Acari: Tetranychidae), the red spider mite (RSM), is a major pest of tea (Camellia sinensis) in most tea-producing countries. Nymphs and adults of RSM lacerate cells, producing minute characteristic reddish brown marks on the upper surface of mature leaves, which turn red in severe cases of infestation, resulting in crop loss. The pest is present on tea all the year round, although numbers vary depending on season. Their number increases as the weather warms up and decreases markedly once rains set in. Under optimal conditions there may be 22 overlapping generations in a year. Parthenogenesis is known to occur; consequently, all mite stages can be found at a given time. Their infestation is mainly confined to the upper surface of the mature leaves and could readily be identified by the bronzing of the leaf. There are several naturally occurring insect predators, such as coccinellid and staphylinid larvae, lacewing larvae, and mite predators, most importantly species of the families Phytoseiidae and Stigmaeidae. Integrated management has been adopted to control this mite pest, involving cultural, mechanical, physical, biological and chemical methods. This review collates the most important works carried out on biology, ecology and management of O. coffeae. Also the scope of future studies for better management of this regular mite pest of tea is discussed.

Insect pests of tea and their management

Globally, 1031 species of arthropods are associated with the intensively managed tea Camellia sinensis (L.) O. Kuntze monoculture. All parts of the plant, leaf, stem, root, flower, and seed, are fed upon by at least one pest species, resulting in an 11%-55% loss in yield if left unchecked. There has been heavy use of organosynthetic pesticides since the 1950s to defend the plant against these pests, leading to rapid conversion of innocuous species into pests, development of resistance, and undesirable pesticide residues in made tea. As a result of importer and consumer concerns, pesticide residues have become a major problem for the tea industry. Integrated pest management (IPM) may help to overcome the overuse of pesticides and subsequent residues. We review the advances made in our understanding of the biology and ecology of major insect and mite pests of tea, host plant resistance, cultural practices, biocontrol measures, and need-based application of botanicals and safer pesticides to understand the present status of IPM and to identify future challenges to improvement.