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• Biological Characteristics of the Whitefly Bemisia tabaci(Gennadius) (Homoptera: Aleyrodidae) on Four Cassava Cultivars

  Le Ngoc Anh, Nguyen Duc Khanh, Ho Thi Thu Giang

  Date Received: 05-05-2021 / Date Accepted: 09-12-2021

   Abstract PDF (VIETNAMESE)

  The objectives wereto determine the biological characteristics of the whitefly (Bemisia tabaci) on 4 cassava cultivars under laboratory conditions at 30C and 70% relative humidity. The experiments were carried out using individual rearing method and the following biological characteristics were evaluated: the developmental time of each stage and its lifecycle, fecundity, female adult longevity, sex ratio and mortality rate of the nymphs on KM419, H34, KM98-7and KM94cassava cultivarss. On four cassava varieties, the longest and lowest life cycle of B. tabaciwere recorded on KM98-7(24.50 days) and KM94variety (22.73 days), respectively. The highest and lowest mortality rate were observed on KM98-7and KM94varieties, respectively. Lifetime fecundity of whitefly varied from 33.00 to 40.09 eggs/female, with the highest fecundity (40.09 eggs/female) observed on KM419 variety. Mean adult longevity of females varied from 4.93 to 5.47 days. Results obtained in this study indicated that cassava varieties significantly affected the lifecycle and fecundity of whitefly. Lower development of whitefly was recorded on the KM98-7 variety.

• Whitefly (Bemisia tabaci Gennadius) on Cassava in Vietnam:  Cryptic Species and Transmission Characteristics  of Sri Lankan Cassava Mosaic Virus (Begomovirus stanleyi)

  Tran Van Chien, Nguyen Thanh Sang, Bui Quoc Viet, Nguyen Dan Truong, Vo Trung Kien, Trinh Xuan Hoat, Ha Viet Cuong

  Date Received: 24-11-2025 / Date Accepted: 01-02-2026 / Date Published: 28-02-2026

   Abstract PDF (VIETNAMESE)

  This study aimed to identify the cryptic species of the whitefly (Bemisia tabaci) infesting cassava in Vietnam and to characterize its transmission of Sri Lankan cassava mosaic virus (SLCMV) (Begomovirus stanleyi). The study employed mitochondrial cytochrome c oxidase subunit I (mtCOI) gene sequence analysis of 47 whitefly samples collected from cassava plants in 10 provinces, together with experiments assessing the virus transmission ability of whiteflies. The results showed that all whitefly samples belonged to the cryptic species AsiaII-1. The AsiaII-1 population on cassava in Vietnam and across Asia, mainly in Southeast Asia, exhibited a small effective population size, low genetic diversity, and dominance of haplotype H2. The minimum acquisition access period and inoculation access period for SLCMV were 1 hour and 15 minutes, respectively. Female whiteflies transmitted the virus more efficiently than males; the virus was transmittable through mating between adult whiteflies, whereas whitefly age had no clear effect on transmission efficiency. In conclusion, this study provides a scientific basis for the development of effective management strategies for cassava mosaic disease in Vietnam.

  DOI: https://doi.org/10.31817/tckhnnvn.2026.24.2.06

• Status And Impact of Epidemiological Factors on Cassava Mosaic Disease (Begomovirus stanleyi) in Vietnam

  Tran Van Chien, Le Thi Lan Huong, Nguyen Hoang Trung Anh, Nguyen Minh Trang, Trinh Xuan Hoat, Ha Viet Cuong

  Date Received: 23-04-2025 / Date Accepted: 14-08-2025 / Date Published: 28-08-2025

   Abstract PDF (VIETNAMESE)

  Cassava mosaic disease is the most serious disease affecting cassava worldwide and its is caused by at least 11 viruses belonging to the genus Begomovirus. In Vietnam, cassava mosaic disease was first reported in Tay Ninh province in 2017 and rapidly spread throughout the country. The objectives of this study were to assess the status of cassava mosaic disease in major cassava-growing regions, identify epidemiological factors influencing the disease, and confirm its causal agent. Field surveys conducted in 2022 showed that cassava mosaic disease was present in 10 out of 12 surveyed provinces, with an average disease prevalence of 70.4%. The average disease incidence (DI), disease severity index (DSI), and adult whitefly (Bemisia tabaci) density were 75.4%, 2.80, and 2.51 individuals per plant, respectively. Statistical analyses revealed that: (i) cassava variety determined DI, DSI, and whitefly density; (ii) plant age influenced DSI; (iii) plants propagated from infected cuttings had higher DSI than those infected via whiteflies; (iv) adult whitefly density had a slight effect on DI but no effect on DSI. PCR testing of 507 cassava leaf samples and sequencing of 15 virus isolates confirmed that Sri Lankan cassava mosaic virus (Begomovirus stanleyi) was the sole causal agent of cassava mosaic disease in Vietnam at the time of investigation.

  DOI: https://doi.org/10.31817/tckhnnvn.2025.23.8.02

• Parasitism of the Parasitoid Encarsia sp.(Hymenoptera: Aphelinidae) on whitefliesBemisia tabaci(Gennadius) (Hemiptera: Aleyrodidae)

  Pham Thi Hieu, Tran Thi Thu Phuong, Pham Hai Chi

  Date Received: 29-08-2023 / Date Accepted: 07-03-2024 / Date Published: 12-06-2025

   Abstract PDF (VIETNAMESE)

  This study aimed to investigate the parasitism rate of Encarsia sp.on B. tabacias well as the impact of host age, host density and parasitoid density on its parasitism. The survey on natural Encarsiaparasitism was conducted on the eggplant fields at Gia Lam, Hanoi at 7 days interval. The results showed that Encarsia sp.had the highest parasitism rate (58.57%) in the middle of June and declined afterward. The parasitoid and whiteflies were mass rearing in the laboratory and recorded for the parasitism rate in 24 hours with different host age (1st-4thinstar nymphs), host densities (5-80 nymphs(3rd-4thinstar)/ leave) and parasitoid densities (1-4 females/ 50 nymphs (3rd-4thinstar). Encarsia sp. reached the highest parasitised percentage at 3rdinstar nymph and lowest at 1stinstar nymph. As the host density increased the parasitism rate decreased, but the emerge rate increased, however. Nevertheless, parasitism increased with increased parasitoid density, but the average parasitism per female decreased. At densities of 1-2 female parasitoids the emerge rate was higher than at 3-4 female parasitoids.Overall, Encarsia sp. had high parasitism rate on the field and host age, host and parasitoid density influenced its parasitism.

  DOI: https://doi.org/10.31817/tckhnnvn.2024.22.3.

• Parasitism of the Parasitoid Encarsia sp.(Hymenoptera: Aphelinidae) on whitefliesBemisia tabaci(Gennadius) (Hemiptera: Aleyrodidae)

  Pham Thi Hieu, Tran Thi Thu Phuong, Pham Hai Chi

  Date Received: 29-08-2023 / Date Accepted: 07-03-2024 / Date Published: 12-06-2025

   Abstract PDF (VIETNAMESE)

  This study aimed to investigate the parasitism rate of Encarsia sp.on B. tabacias well as the impact of host age, host density and parasitoid density on its parasitism. The survey on natural Encarsiaparasitism was conducted on the eggplant fields at Gia Lam, Hanoi at 7 days interval. The results showed that Encarsia sp.had the highest parasitism rate (58.57%) in the middle of June and declined afterward. The parasitoid and whiteflies were mass rearing in the laboratory and recorded for the parasitism rate in 24 hours with different host age (1st-4thinstar nymphs), host densities (5-80 nymphs(3rd-4thinstar)/ leave) and parasitoid densities (1-4 females/ 50 nymphs (3rd-4thinstar). Encarsia sp. reached the highest parasitised percentage at 3rdinstar nymph and lowest at 1stinstar nymph. As the host density increased the parasitism rate decreased, but the emerge rate increased, however. Nevertheless, parasitism increased with increased parasitoid density, but the average parasitism per female decreased. At densities of 1-2 female parasitoids the emerge rate was higher than at 3-4 female parasitoids.Overall, Encarsia sp. had high parasitism rate on the field and host age, host and parasitoid density influenced its parasitism.

  DOI: https://doi.org/10.31817/tckhnnvn.2024.22.3.

• Identification of Transmission Manners of Sri Lankan cassava mosaic virus (SLCMV) causing Cassava Mosaic Disease in Vietnam

  Trinh Xuan Hoat, Nguyen Chi Hieu, Ngo Quang Huy, Nguyen Duc Huy

  Date Received: 30-09-2020 / Date Accepted: 05-01-2021

   Abstract PDF (VIETNAMESE)

  ThisstudywasconductedtodeterminethetransmissionmannersofSriLankancassavamosaicvirus(SLCMV)causing cassavamosaicdisease(CMD).Thepupaofwhitefly (Bemisia tabaci) was collectedfromthefieldand and lettodeveloptoadultsonthedisease-freecassava plantsin the pots.Thedisease-freeadultwhiteflieswereisolatedinacagefortwo months toobtain anon-viruliferouscolonyofwhitefliesfor the inoculation experiment.Thenumberofwhitefliesintroducedindisease-freecassavawas 5,10and20andthefeedingperiod(inoculation)ondisease-freecassavawas2,6,12and24hrs.Thiswasreplicatedforthreetimesand 10 plant/replication.To identify the transmission manner via cuttings, cuttings from symptomatic and asymptomatic plants of KM94,HL-S11and KM419planted in Dong Nai province were grown in insect resistant cages and caculate the number of diseased plants. The results indicated that viruliferousB.tabaciadultstransmittedSLCMVwithvariousdegreesofefficiencydependingonthenumberofadultsusedtotransmitandfeeding duration. The disease incidence ranged from 25.0-90.0%. Symptoms started from the top leaves. The latent period ranged from 20 to 25 days.After20-30daysofplantingtheCMD-infectedKM94,HL-S11andKM419varieties,itbegantoshowtypicalsymptomsofCMDwithleafcurl,wrinkling,mosaicandinconsistentwithdiseaserateof100%;meanwhile,inthecontroltreatmentthatusinghealthycuttingsfromthesamevarietiesshowednosymptoms.AllthetestedplantsweresubjectedtoPCRanalysisusingprimerpairSLCMV-A-F1/SLCMV-A-R2,directsequencingandDNAanalysis.TheallsymptomaticplantswerepositivewithSLCMV.ThestudyhasprovidedessentialinformationonthetransmissionofSLCMVviaeitherplantingmaterialsorthewhiteflyvectorthatwillhelptounderstandthespreadofSLCMVinthefieldandfacilitatethepredictionofvirusepidemicsinVietNam.