Reference genes for gene expression studies by RT-qPCR in Brevipalpus yothersi (Acari: Tenuipalpidae), the mite vector of citrus leprosis virus.

Quantitative reverse transcription PCR (RT-qPCR) is a high-throughput method to analyze the transcriptional expression of genes. Currently, no reference genes have been described for evaluating gene expression in Brevipalpus yothersi, the false spider mite, a polyphagous that act as vector of the citrus leprosis virus C (CiLV-C), an important citrus disease. This study aimed to identify the most stable reference genes in B. yothersi. The RT-qPCR expression data for selected genes were evaluated from three conditions: different developmental stages, plant hosts and acquisition of CiLV-C. To analyze the stability of the candidate reference genes we used ΔCq method, GeNorm, NormFinder, BestKeeper and RefFinder. Ubiq and GAPDH are best suited for normalizing gene expression data in viruliferous and non-viruliferous mites. Ubiq, EF1α and GAPDH are the most stable for different developmental stages. RPL13 and RPL32 are the best reference genes for approaches to B. yothersi in different host plants. Considering all the experimental conditions, Ubiq, EF1α, and GAPDH were the most stable genes. Here we developed an accurate and comprehensive RT-qPCR strategy for use in B. yothersi gene expression analysis. These results will improve the understanding of the biology of the false spider mites and their role as virus vectors.

Interaction of spirodiclofen with insecticides for the control of Brevipalpus yothersi in citrus.

BACKGROUND: The mite Brevipalpus yothersi (Acari: Tenuipalpidae) is of great importance in citriculture because it is a vector of the disease citrus leprosis. The frequency of application of a combination of pesticides has increased because of an increase in the occurrence of economically important pests of citrus. However, the combined effect of acaricide and other insecticides targeting B. yothersi is unknown. The objective of this study was to evaluate the effect of a combination of spirodiclofen and other insecticides on the control of B. yothersi. RESULTS: Analysis using spirodiclofen alone resulted in 97.22% efficiency in the control of B. yothersi on day 7 after application. A combination of spirodiclofen with either phosmet or imidacloprid resulted in 55% and 59% efficiency, respectively. A reduction in the efficiency of mite control by up to 42% was observed when the mites were exposed to a combination of acaricide with other insecticides. CONCLUSIONS: Application of a combination of spirodiclofen with phosmet or imidacloprid compromises the efficiency of acaricide in the control of B. yothersi. © 2018 Society of Chemical Industry.

Infestation dynamics of Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) in citrus orchards as affected by edaphic and climatic variables.

Brevipalpus phoenicis (Geijskes) is a cosmopolitan and polyphagous mite that transmits important phytoviruses, such as coffee ringspot virus, passion fruit green spot virus and Citrus leprosis virus C. To characterise the dynamics of the probability and the rate of B. phoenicis infestation in response to edaphic and climatic factors, monthly inspections were performed in nine orchards in a citrus region of the State of Bahia, Brazil, for 35 months. Three fruits per plant were examined using a magnifying glass (10×) on 21 plants distributed along a "W"-shaped path in each orchard. Meteorological data were collected from a conventional station. To determine the correlations among the climatic variables, the data were analysed using Spearman correlations. Variables were selected by principal component analysis, and those that contributed the most to differentiate the groups were evaluated via a Mann-Whitney test. Using the quantile-quantile method, the limit values for the following climatic variables were determined: temperature (24.5 °C), photoperiod (12 h), relative humidity (83%), evapotranspiration (71 mm) and rainy days (14 days). The combination of longer days, higher temperatures, lower relative humidity levels and lower evapotranspiration increased the probability of B. phoenicis infestation, whereas successive rain events decreased that risk. Infestation rates were negatively affected by relative humidity levels above 83% and were positively affected by a decreasing available soil-water fraction and increasing insolation and photoperiod.