Đặc điểm sinh học, sinh thái và biện pháp phòng chống rệp sáp giả paracoccus marginatus william and granara de willink (homoptera pseudococidae) hại cây đu đủ tại hà nội tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURAL SCIENCES DOAN THI LUONG THE BIOLOGICAL AND ECOLOGICAL CHARACTERISTICS AND CONTROL MEASURES OF PSEUDO-MEALYBUG Paracoccus marginatus Williams and Granara de Willink (Homoptera: Pseudococidae) CAUSING DAMAGE ON PAPAYA IN HANOI Specialization : Plant protection Code : 62 01 12 HA NOI - 2019 LIST OF THESIS-RELATED PUBLICATIONS SUMMARY OF AGRICULTURE PhD THESIS This thesis was completed at Vietnam Academy of Agricultural Sciences Scientific Supervisors: Prof Dr Nguyen Hong Son Reviewer 1: Reviewer 2: Reviewer 3: The thesis will be defended at the Academy-level thesis examination Council of Vietnam Academy of Agricultural Sciences At o’clock day month year 201 The copy of this thesis will be found at: National Library of Viet Nam Library of Vietnam Academy of Agricultural Sciences Library of Plant Protection Research Institute Doan Thi Luong, Pham Van Lam, Le Thi Tuyet Nhung, Truong Thi Huong Lan, “Result of identification of The Mealybug , Pseudococcidae (Homoptera) infesting Papaya around the suburb of hanoi”, Journal of Plant Protection (6)/2018, pages 10-14 Doan Thi Luong, Le Thi Tuyet Nhung, Nguyen Hong Son, Pham Van Lam, “Bio-ecological Characteristics of the Papaya Mealybug, Paracoccus marginatus Williams and Granara de Willink (Homoptera: Pseudococcidae) under Laboratory Conditions”, Journal of Plant Protection (6)/2018, pages 3-10 Doan Thi Luong, Khuat Thi Phuong, Ho Thi Thu Giang, Nguyen Hong Sơn, Nguyen Van Liem, “Population dynamic of Paracoccus marginatus Williams and Granara de Willink (Homoptera: Pseudococcidae) on papaya in bub-urban of Hanoi ”, Journal of Agriculture and Rural development (354+355)/ 2019, pages 310-319 intercropped with maize was lower than that on monoculture papaya (19.1 individuals/leaf and 1.32 individuals/fruit compared with 51.3 individuals/leaf and 5.4 individuals/fruit) P marginatus on monoculture papaya appeared earlier with density (256.5 individuals/leaf and 4.7 individuals/fruit) always higher than in papaya rotated with sweet potato (72.1 individuals/leaf and 2.2 individuals/fruit) 1.5 Such cultivation techniques as rotation planting, intercropping and high pressure watering on the leaves all have the effect of limiting density of P marginatus The use of lower toxic chemicals liked Spirotetramat and Pymetrozine (registered for mealybug on fruit trees) is highly effective in the field (86.42% and 83.8%, respectively) Rotenone, Abamectin and Petroleum spray oil (registered to control mealybugs on fruit trees) which can provide 72% control of P marginatus in the field condition, can be used alternately with Spirotetramate and Pymetrozine for substitution of chemical pesticides of toxic group that farmers are using commonly on papaya nowadays but not legally allowed to be used on fruit trees Spraying pesticides at 1st and 2nd instar nymphs of P marginatus with a minimum amount of water of 1000 liters/ha and spraying with pressure compressing pump will bring optimal control II Recommendations Control of P marginatus is real difficulty, so it is advised to apply integrated measures as recommended in conclusion 1.4 and the proper technique of pesticide use in conclusion 1.5 of this thesis for ensure of effectiveness Especially for centralised planting areas, it is advisable to apply appropriate rotation system with crops that are not the favorable hosts for P marginatus such as corn, vegetables and beans to reduce accumulation of pseudo-mealybug density on the field INTRODUCTION Reasonale Papaya is often attacked and damaged by mealybugs, white fly, small spiders, fruit flies, especially damaged by mealybugs Even though, there have been no in-depth studies on insect pests on papaya as well as on mealybugs on papaya in Vietnam up to date A comprehensive understanding of the species composition, biological and ecological characteristics of papaya mealybug will be the scientific basis to propose measures to manage them effectively and environmentally This thesis will focus the research on "Biological, ecological characteristics and control measures to control mealybug Paracoccus marginatus Williams and Granara de Willink (Homoptera: Pseudococidae) damaging papaya in Hanoi" Objective of the research The the reserach aims to determine species composition of mealybugs, biological and ecological characteristics of P marginatus damaging papaya and the effective measures to control of P marginatus, hence, building and proposing protocol to manage P marginatus effectively, economicaly and environmentally in some papaya growing areas in Hanoi Scientific and practical significance 3.1 Scientific significance The thesis provided scientific data on species composition of mealybugs on papaya in Hanoi; providing basic biological and ecological characteristics of P marginatus and the effective control measures to that insect in papaya growing areas of Hanoi 3.2 Practical significance The research findings of the thesis are the scientific basis to develop an effective and environment sound protocol for control of P marginatus New research findings - It is the first time recorded Paracoccus marginatus Williams and Granara de Willink (Homoptera: Pseudococcidae) damaging 24 papaya in Vietnam - Providing new scientific data on biological and ecological characteristics, especially data on life table, population dynamic of Paracoccus marginatus in Hanoi, hence updating systematically scientific data on Paracoccus marginatus on papaya in Hanoi - Providing scientific data on the effectiveness of feasible measures including cultivation, mechanical and chemical measures for effectively and environmentally control of Paracoccus marginatus on papaya in Hanoi The thesis structure The thesis is structured in 151 pages, including introduction, content (3 chapters), conclusions and recommendations with 28 tables of data and 26 figure Reference is made from 107 documents, including 36 Vietnamese and 71 English documents CONCLUSIONS AND RECOMMENDATIONS I Conclusions 1.1 It is the first time recorded P marginatus Williams and Granara de Willink (Homoptera: Pseudococcidae) damaging papaya in Hanoi At least 13 plant species belonging to 11 botanical families in the agricultural ecosystem in the suburbs of Hanoi were recorded as food plants of P marginatus 1.2 Under stable conditions (25°C and 30°C, 80% RH, and a photoperiod of 16L:8D) and Taiwan's papaya leaves using as food, the female of P marginatus has the style of hemimetamorphosis and the male has hypermorphosis Life cycle is 25.56-30.31 days Female of P marginatus can reproduce parthenogenetically (although there are 61.0-61.1% of males in the population) Fecundity is 233.53462.2 eggs/female Females can live from 14.42 to 21.15 days and male adults can only live from 1.77 to 1.88 days 1.3 At a temperature of 25°C, net reproductive rate (Ro), the intrinsic rate of increase (Rm), the finite rate of increase (λ), mean generation time (Tc) ) and the doubling time (DT), respectively, reached 457,87 ♀/♀, 0.188 ♀/♀/day, 1.19 times, 34.71 days and 3.93 days At 30°C, depending on each parameter, its value can be increased or decreased compared to at 25°C and reached 367,79 ♀/♀, 0,197 ♀/♀/day, 1.22 times, 28.17 days and 3.52 days, respectively There are 11 generations/year in green house 1.4 The density of P marginatus on Hong Phi papaya variety (the highest density is 255.0-256.5 individuals/leaf and 6.5-7.3 individuals/fruit) is significantly higher than that on dwarf variety (28.2 individuals/leaf and 0.48-0.52 individuals/fruit) The density on 1–year-old papaya (255.0 -256.5 individuals/leaf and 6.5-7.3 individuals/fruit) is higher than that on 2–year-old papaya (53.1-53.8 individuals/leaves and 14,2-14,5 individuals/fruit) The density on intercropped papaya is higher than that on monocultured papaya (83.5 individuals/leaf and 13.2 individuals/fruit compared to 53.1 individuals/leaf and 4.26 individuals/fruit) The density on papaya 23 pesticides including Spirotetramate, Abamectin, Petroleum spray oil and Pymetrozine with various sprayers such as hand compressing sparyer, hand pre-compressed sprayer and motor compressed sprayer The result showed that when spraying with the conventional hand compressing sprayer the efficacy of insecticides decreased significantly compared to that when sprayed by pre-compressed sprayer (49.70 - 62.87% compared to 68.88 - 81.98%) When spraying by motor sprayer, the pesticide efficacy was not improved even decreased compared to spraying with hand compressing sprayer and pre-compressed sprayer 22 Chapter LITERATURE REVIEW AND SCIENTIFIC BACKGROUND OF THESIS 1.1 Scientific background The diversity of ecological and farming system (intensive, intercropping, rotation, varieties and farming techniques) has a very complex impact on insect community on papaya, including mealybugs Therefore, the determination of mealybug composition, biological and ecological characteristics, population dynamic and control measures against P marginatus are an important scientific basis to develop effective control measures of this most common and important insect pest in Vietnam 1.2 Oversea research findings on Paracoccus marginatus 1.2.1 Research on classification, distribution and damage of Paracoccus marginatus 1.2.1.1 Classification of P marginatus According to Williams and Granara, papaya mealybug P marginatus belongs to the Kingdom Animalia, Phylum Arthropoda, Class Insecta, Subclass Pterygota, Order Homoptera, Suborder Sternorrhyncha, Superfamily Coccoidea, Family Pseudococcidae, Genus Paracoccus, Species P marginatus Williams and Granara de Willink 1.2.1.2 Origin, distribution and invasion of the papaya mealybug Paracoccus marginatus Papaya mealybug, P marginatus native to Mexico, Central America and distributed in tropical Americas, began to invade out of the natural distribution area since 1992 and quickly became an invasive alien species in many islands in the Caribbean, Central America and South America Up to now, it has been recorded in biogeological regions of the world: neotropical, nearctic, oceania/ Australia, oriental/Indo-Mala and Afrotropical (Ben-Dov, 2012; Heu et al., 2007; Meyerdirk et al , 2004; Miller et al., 1999; Muniappan et al., 2006, 2008) 1.2.2 Study on morphological characteristics of Paracoccus marginatus Morphological characteristics of adult, egg and nymph of P marginatus were described in Al-Helal et al (2012), Mani Chellappan et al (2013b), Miller et al (1999), Sharma et al (2013), Tanwar et al (2010), Walker et al (2003), Wu et al (2014), 1.2.3 Study on biological and ecological characteristics of Paracoccus marginatus Details of the biology and ecology of P marginatus can be found in the literature of Amarasekare et al (2008a, 2008b), Hintenou et al (2015), Mani Chellappan et al (2013b), Thangamalar et al (2010) and Walker et al (2006) 1.2.4 Research on control of Paracoccus marginatus Control of P marginatus by integrated pest management measures including phytosanitary, cultivation and manual, biocontrol with using botanical and chemical pesticides (Banu et al., 2010; Galanihe et al., 2010; Krishnan et al., 2016; Mani et al., 2012; Muniappan, 2014; Saengyot amd Burikam, 2011; Seni and Chongtham, 2013; Sharma et al., 2013; Tanwar et al., 2010;…) 1.3 Research on Paracoccus marginatus on papaya in Vietnam 1.3.1 Detection of Paracoccus marginatus in Vietnam P marginatus was firstly recorded in Vietnam on cassava (Le Thi Tuyet Nhung et al., 2014, 2015) So far there has been no publication regarding this species on papaya 1.3.2 Morphological characteristics of Paracoccus marginatus Research results on the species composition of mealybugs (Pseudococcidae) were published by Nguyen Thi Chat (2008), Nguyen Thi Chat et al (2005), Pham Van Lam (2013), Le Thi Tuyet Nhung et al (2018),… but very limitation of their morphological characteristics were described 1.3.3 Biological and ecological characteristics of Paracoccus marginatus So far, there have been no research on biological and ecological characteristics of P marginatus in Vietnam 3.4.2.2 Effect of pesticides to control P marginatus on the field It was shown from small scale trials that, athough the efficacy to control P marginatus by pesticides was significantly lower than that in the Lab Test, all chemicals provided high and stable efficacy (from 80.27% to 87.32%) after days of spraying Of which, Cypermethrin + Chlorpyrifos Ethyl brought the highest efficacy of 87.32%, followed by Carbosulfan (86.5%) Both low toxic pesticides Spirotetramat and Pymetrozine showed high potency, respectively 86.42% and 83.8% Biological and botanical pesticides also showed a high potency from 66.83% to 78.01%, of them, Abamectin achieved the highest effect 78.01%, then Petroleum spray oil and Rotenone achieved 72.8% and 72.57%, respectively, at days after spraying Observation from large scale experiments conducted with 05 pesticides including: low-toxic chemicals selected from common registered pesticides to control mealybugs on fruit trees and 03 bio and botanical pesticides also indicated that at 10 days after spraying, the effectiveness of Spirotetramate reached the highest of 84.79% Biological and botanical pesticides have good and prolonged efficacy (67.95% - 76.96%) 3.4.2.3 Efficacy of pesticides against different developmental stages of Paracoccus marginatus Experiments to determine the efficacy of Spirotetramat and Pymetrozine to control P marginatus at different instar indicated that both insecticides are highly effective for control 1st and 2nd instar nymph of Paracoccus marginatus at days after spraying The efficacy is gradually reduced when apply against 3nd instar 3.4.2.4 Efficacy of pesticides applied with different water volume to control Paracoccus marginatus The efficacy pesticides to control P marginatus after days of spraying was highest when spraying at 1000 liters/ha compared to 600 and 800 liters/ha 3.4.2.5 Efficacy of pesticides applied with different sparyers to control Paracoccus marginatus Experiments were conducted to investigate efficacy of 4 21 marginatus is significantly decreased compared to density in plot washing at by compressor spraye rat 1000lit/ha in day only Therefore, this method can be applied to manage P marginatus when the density is low 3.4.2 Chemical application The use of pesticides is a last measure when efforts to apply other measures are not likely to prevent the outbreak of P marginatus According to the list of pesticides allowed to be used in Vietnam, issued together with the Ministry of Agriculture and Rural Development’s Circular No 03/2018 / TT-BNNPTNT dated February 9, 2018, there are currently no pesticides registered to use for control of P marginatus on papaya Meanwhile, in production, farmers have to choose different types of mealybug on other crops, including chemical pesticides belong to toxic group that are not allowed using to control mealybugs in fruit trees This research has focused on assessment of 14 pesticides, including chemical activities (including active ingredients are commonly used by farmers in papaya growing areas and low-toxic active ingredients selected from common registered pesticides to control mealybugs on fruit trees such as Spirotetramat; Pymetrozine), and bio- and botanical pesticides selected from popular registration pesticides to control mealybugs on fruit trees 3.4.2.1 Effect of pesticides to control P marginatus in laboratories - For chemical pesticides: all tested chemicals brough 86-100% efficacy to control P marginatus, the highest is Carbosulfan (100%), followed by Pyridaben+Abamectin (97.33%) Two commonly registered low-toxic chemical pesticides can control 97.33% and 94.67% P marginatus - For bio- and botanical pesticides: Observations indicated that after days of spraying, the pesticides brough a relatively high efficacy of to control P marginatus (70.67% - 81.33%) Among the experiment, two pesticides provided high efficacy over 80% (Abametin and Petroleum spray oil) 1.3.4 Control of Paracoccus marginatus on papaya To date, no researchs on control of P marginatus has been conducted in Vietnam 20 CHAPTER MATERIALS, CONTENTS AND METHODS OF THE STUDY 2.1 Location and time of study - Laboratory, green house of Plant Protection Research Institute - Papaya growing areas in 03 communies of Hanoi: Phung Thuong commune (Phuc Tho district), Dan Phuong commune (Dan Phuong district), Di Nau commune (Thach That district) - Research period: 2015 - 2018 2.2 Research content - Surveying papaya insect pests and determining the main pests of papaya in Hanoi - Determining biological and ecological characteristics of papaya mealybug P marginatus in laboratory - Study on population dynamic and factors affecting the population density of P marginatus on papaya in the study area - Research on IPM measures of P marginatus on papaya 2.3 Materials and tools for research Materials The source of P marginatus used in the study was collected from papaya orchards in Hanoi The Hong Phi - Taiwanese papaya variety was used to feed P marginatus in lab experiments Two varieties (Hong Phi papaya – Taiwan and high yielding dwarf papaya –Thailand) were used in field study Tools and equipments Stereo microscope: Carl Zeizz Stemi 2000-C and microscope: Carl Zeizz Promostar with a maximum magnification of 1000 times Air - controlled insect rearing chamber: DAEYANGETS model GC-101B (RGX-400E brand) with temperature, humidity and light control system Other laboratory equipment: insect-proof plastic boxs, petri boxes, tubes, insect needles, lame, lamen, plastic pots, insect netting cages, green houses, quills, blotting paper, sample containing jars, nylon bags, Chemicals 96% alcohol, KOH, H2SO4, alcohol acid, clove oil, canola glue, some pesticides to control mealybugs, etc 2.4 Research methodology 2.4.1 Method of surveillence the species composition of papaya pests and determining the main pests of papaya in Hanoi 2.4.1.1 Method to survey pests on papaya Following the survey method of the Plant Protection Research Institute (1997) and the National Technical Regulation on methods of survey and detection of plant pests QCVN 01- 38: 2010/ BNNPTNT The interval between two surveys is 14 days on a fixed day of the month 2.4.1.2 Method to identify of papaya pests Follow the method of Watson (2007), and identify their scientific name according to keys of Williams and Willink (1992), Williams and Watson (1988, 1990) Lame specimens after identification have been to verify by Dr Natalia von Ellenrieder (from the Center for Pest Control in California Department of Agriculture and Food) The scientific name of other pests collected on papaya were determined by viẹtnamese taxonomists 2.4.2 Method of studying morphological, biological and ecological characteristics of papaya mealybug P marginatus in laboratory 2.4.2.1 Study on morphological characteristics Observing 30 individuals with a hand-held and stereoscope microscope for the egg/egg sac and the length, width of the egg (mm), egg color, body length and width, number of beard burns 2.4.2.2 Research on biology and ecology characteristics Following the method of Amarasekare et al (2008a) with improvements to suit the experimental conditions P marginatus were individualy raised in air - controlled chamber (model RGX400E) at 25ºC, 30ºC, 80% RH and photoperiod of 16L:8D Observing 3.3.4 Effect of rotation on the density of P marginatus on papaya In Thach That, farmers usually grow monoculture papaya or year old papaya rotated with potatoes, chilli, vegetables, etc Observation showed that in monoculture gardens, P marginatus began to appear on leaves from March 2017 with a low density, an average of 0.8 individuals/leaf Then increased, especially increasing rapidly from mid-April and peaking first time from 29 June 2017 to July 2017 (with 39.3 - 39.8 individuals/leaf, 4.8 - 6.3 individuals/fruit) and second time at 19 October 2017 (with 256.5 individuals/leaf, 4.7 individuals/fruit) When rotation with potato, P marginatus started to appear on papaya leaves later with lower density (0.30 individuals/leaf) and then increased rapidly from the end of April and the get the first peak from 29 June 2017 to July 2017 (with 21.3 - 22.5 individuals/leaf, 2.9 - 3.5 individuals/fruit) and second pick at 19 October 2017 (with 72.1 individuals/leaf, 2.2 individuals/fruit) 3.4 IPM measures of Paracoccus marginatus damage on papaya 3.4.1 Cultivation measures 3.4.1.1 Using tolerant varieties The surveillence indicated that density of P marginatus on the high yielding dwarf variety is significantly lower than that on Hong Phi variety So that, using dwarf papaya variety is advised to limit the density and damage of P marginatus, hence limitation use of pesticides 3.4.1.2 Intercropping It was also found from population dynamic study that when intercropping with maize, the density of P marginatus was much lower than that of monoculture gardens, while the density of P marginatus in intercropping with bananas was higher than that of monoculture papaya Thus, to limit the damage of P marginatus, farmers should not be recommended to intercrop bananas in papaya garden as it has been practicing in some localities 3.4.1.3 Watering on the leaves with a high pressure pump When washing the leaves with water at 2000 or 3000 liters/ha by high pressure pump during consecutive days, the density of P 19 3.3.2 Population dynamic of Paracoccus marginatus on papaya at different ages The regular observation on 1-year-old papaya indicated P marginatus appears on leaves from early March and on fruits from early May, forming two peaks of density in late June to early July and mid-October Where as, P marginatus occures year-round on 2year-old papaya, but only forming two peaks (in late June and midOctober to early November) on the leaf The density at the first peak is many times higher than that at the second peak The density of P marginatus in the one-year-old papaya garden is always higher than that on the two-year-old papaya 3.3.3 Population dynamic of Paracoccus marginatus in monoculture and intercropped gardens When intercropping with banana in Phuc Tho district, the P marginatus population is low during January to March but higher than that in the monoculture garden of papaya (from January to May) Then the density began to increase from the beginning of April (earlier than monoculture garden) and formed two peaks on June 29, 2017 (with 49.1 individuals/leaf, 6.22 individuals/fruit) and on Nov 2017 (with 83.4 individuals/leaf, 13.2 individuals/fruit), markedly higher than density in the monoculture garden (peaked on 29 June 2017 at 16.2 individuals/leaf, 1.6 individuals/fruit, and on Nov 2017 at 53.1 individuals/leaf, 4.26 individuals/fruit) When applying maize intercropped in papaya garden at Thach That, P marginatus population during the period from January to mid-May was low, averaging of 2.2 - 5.5 individuals/leaf, 0.1 - 1.3 individuals/fruit After that, the density began to increase, forming two peaks: pick from June 22 to June 29 2017 (with 8.7 - 9.5 individuals/leaf, 0.8 - 1.96 individuals/fruit), and pick at November 2017 (with 19.1 individuals/leaf, 1.32 individuals/fruit), significantly lower than the density in monoculture orchard (peak from June 22 to 29 2017 at 16.1 - 16.2 individuals/leaf, 8.7 - 9.5 individuals/fruit, and peak on November 2017 at 51.3 individuals/leaf, 5.4 individuals/fruit) the life cycle; population development criteria such as net reproductive rate (Ro), the intrinsic rate of increase (Rm), the finite rate of increase (λ), mean generation time (Tc) and doubling time (DT), and adjusted with formular of Birch (1948) and Kakde et al (2014) 2.4.3 Method of studying on population dynamic and factors affecting the population densities of Paracoccus marginatus Carried out on two papaya varieties: Hong Phi (Taiwan) and high yielding dwarf (Thailan) at various conditions suchs as: plant age (1 year and years old); planting mode (monoculture, intercroping and rotating with potato) Observation was followed survey method of Plant Protection Research Institute (1997) 2.4.4 Method for research on IPM measures of Paracoccus marginatus on papaya 2.4.4.1 Research on cultivation measures The research was conducted with control measures including (i) using resistant papaya varieties (Hong Phi and high yielding dwarf papaya); (ii) intercropping with bananas and maize and (iii) rotating with potatoes The effectiveness of eah control measure was based on the survey of P Marginatus population dynamic on the field as described in section 2.4.3 2.4.4.2 Research methods on effective of manual measures Proceed with a high-pressure watering technique to wash away P marginatus on papaya leaves through large scale experiment on the field, no replicates and 300 m2/plot The experiment was conducted in Di Nau (Thach That, Ha Noi) on years old papaya orchard Treatments included different watering regimes with categories: (i) volumes of 1000, 2000 and 3000 liters/ha; (ii) two sprayers: high-pressure nozzles and compressors sprayer; and (iii) one time watering and times within days, and non-watering as checking plot Water was sprayed evenly on the under and upper surfaces of the leaves at 15.00-18.00 pm Surveying the density of mealybugs before and after watering days Adjusting the efficacy by the Henderson-Tilton formula 18 2.4.4.3 Research methods on pesticides use The study was conducted with the following contents - Surveying the efficacy of pesticides currently used by farmers and alternative bio & botanical pesticides to control P marginatus through Lab tests and small/large scale experiments on the field - Determining effective techniques to use pesticides such as suitable dosage, application timing, water volume and spraying tools Adjusting the efficacy by the Abbot formula for Lab tests and Henderson-Tilton formula for field trials 2.5 Data statistix methods Field data were statistixed with Excel and statistical Window software CHAPTER FINDINGS AND DISCUSSION 3.1 Species composition of papaya pests and main pests damaged papaya in Ha Noi 3.1.1 Species composition of insect and mite pests damaging papaya Have been species belonging to different families of insect and mite orders collected and identified, similar to the number of insects/ mites found on the papaya in Vietnam until 2013 (Pham Van Lam, 2013) However, the majority of insect species (6 species) in this study did not coincide with those recorded on papaya before 2013 3.1.2 Identifying the scientific names of pests collected on papaya It was showed by using the taxonomy keys of Williams (2004), Williams and Watson (1988) that the characteristics of the mealybug species collected on papaya in Hanoi belonging to genus of Paracoccus Ezzat & Mc Connell Folloing the identification key of Williams and Willink (1992), the mophology characteristics observed on Lam sampled, are coincided with characteristics of P marginatus Williams and Granara de Willink species (Figure 3.1) After identification, specimen of mealybug species was sent to the Pest Identification Center of the California Department of Agriculture and Food for re8 3.3 The population dynamic and factors affecting the density of Paracoccus marginatus on papaya in the study area 3.3.1 Population dynamic of Paracoccus marginatus on papaya The survey showed that on high yielding dwarf papaya variety, the density of P marginatus was always much lower and more stable than that in Hong Phi variety at both study sites Density of P marginatus on leaf is always significantly higher than that on fruit The density of P marginatus is highest at the end of October and early November when the temperature is not so lower and little heavy rain occured The density of P marginatus is lowest in August when prolong and strong rainy comes (Figure 3.13; 3.14; 3.15 and 3.16) This is similar with the research results of Walker et al (2003) According to these authors, the heavy rainfall severely reduced the population density of P marginatus Figure 3.13 Population dynamic of P marginatus on leaves of various papaya varieties at Phuc Tho (Ha Noi) in 2017 Figure 3.14 Population dynamic of P marginatus on leaves of various papaya varieties at Thach That (Ha Noi) in 2017 Figure 3.15 Population dynamic of P marginatus on fruits of various papaya varieties at Phuc Tho (Ha Noi) in 2017 Figure 3.16 Population dynamic of P marginatus on fruits of various papaya varieties at Thach That (Ha Noi) in 2017 17 26 days age, then starting to reduce with laying time The last fecundity day of female adult is 41 days age (Figure 3.12) Hình 3.12 Age specific survival rate (lx), age specific fecundity (mx) of P marginatus at 30oC and 80% RH Rearing at a temperature of 25°C, 80%RH, a photoperiod of 16L:8D with papaya leaves as food, the population growth parameters of P marginatus including Ro, Rm, λ, Tc and DT reached 457.87 ♀/♀, 0.188 ♀/♀/day, 1.19 times, 34.71 days and 3.93 days, respectively When rearing at 30°C with the same humidity and food, depending on each parameter, its value reached at 367.79 ♀/♀, 0.197 ♀/♀/day, 22 times, 28.17 days and 3.52 days, respectively (Table 3.16) Table 3.16 Population growth parameters of P marginatus at various constant temperatures (in Plant Protection Research Institute) Testing Giá trị thông số bảng sống conditions Ro rm λ Tc DT 25ºC, 80%RH 457,87 0,188 1,19 34,71 3,93 30ºC, 80%RH 367,79 0,197 1,22 28,17 3,52 3.2.2.8 The number of generations per year of Paracoccus marginatus Observation with P marginatus rearing in green house of Plant Protection Research Institute from May 2015 to May 2016 (17,2-31.3oC and 75-84% RH), indicated that the fastest individual of P marginatus can complete nearly 11 generations a year The 11th generation has completed only in 3rd instar nymph of female sex The shortest living time of one generation was 22.88 days in June when temperature was 31.3oC and humidity was 75% The longest was 46.5-46.67 days in mid December to early March of the next year when rearing at 17.217.4oC and 78-79% RH 16 identification Dr Natalia von Ellenrieder of this Centre also asserts that the mealybug species collected on papaya in Ha Noi was P marginatus Williams and Granara de Willink Its English name is “papaya mealybug” Figure 3.1 Lam specimen of P marginatus collected in Hanoi 3.2 Morphological, biological and ecological characteristics of papaya mealybug, Paracoccus marginatus 3.2.1 Morphological characteristics of Paracoccus marginatus Egg Egg is yellow green, oval shaped about 0.2mm long They are laid in an egg-sac The surface of the egg-sac is covered with a layer of white wax The egg-sac is gradually exposed at the real of the female body and the length of the egg-sac can be times the length of the female body (Figure 3.2) a Egg sac b Egg Figure 3.2 Egg and egg sac of P marginatus Nymph: newly hatched nymph (first instar nymph) is an ovalshaped body, yellowish green, indistinguishable by sex The size is quite small, the body is only 0.5 ± 0.01 mm long and the widest part of the body is only 0.21 ± 0.01 mm (Figure 3.3) Figure 3.3 The 1st instar nymph of P marginatus instar nymph of P marginatus is quite a clear distinction in color and shape of female sex and male sex 2nd instar nymph of female sex is indistinguishable by shape and color from that of 1st instar nymph (Figure 3.4b) The body of a 2nd instar nymph of female sex has a length of 0.84 ± 0.021 mm and the width is 0.43 ± 0.01 mm The 2nd instar nymph of male sex gradually changes from yellowish-green to a pale pink, then gradually darkens to a deep red with the body length of 1.2 ± 0.05 mm and the width of 0.61 ± 0.02 mm (Figure 4a) nd male sex is 89.41-93.02% and at nymph stage in female sex is 89.4196.77% The survival rate at pre-pupa and pupa stages, respectively, are 87.5-95.83% and 85.71-93.48% The survival rate of whole stage (from egg to male) rearing at a temperature of 25°C was significantly higher than that at 30°C, and reached 76.79% and 62.5%, respectively The survival rate at whole stage from egg to female is equivalent at two experimental temperatures, reached 81.83% at 25°C and 81.08% at 30°C This result is similar to studies of Amarasekare et al (2008a, 2008b) 3.2.2.7 Live table of Paracoccus marginatus Rearing at 25ºC, 80%RH, photoperiod of 16L:8D and feeding with papaya leaf, the age specific survival rates (lx) of P marginatus adult is 100% at 34 days age From 35 days age, lx is starting to reduce and sharply decrease from 35 days age After 60 days age, all female adult are died (Figure 3.11) In the above conditions, female adult of P marginatus starts laying egg at 25 days old The highest age specific fecundity (mx) is 40.0 at 30 days age, then starting to reduce At 52 days age, all female adults stops fecundity (Figure 3.11) a 2nd instar nymph of male sex b 2nd instar nymph of female sex nd Figure 3.4 The instar nymph of P marginatus 3rd instar nymph is only found with the female sex Its shape and color is not different from 1st and 2nd instar nymph of female sex (Figure 3.5) Figure 3.5 The 3nd instar nymph of P marginatus 10 Figure 3.11 Age specific survival rate (lx), age specific fecundity (mx) of P marginatus at 25oC and 80%RH Rearing at 30ºC, 80%RH, photoperiod of 16L:8D and feeding with papaya leaf, the age specific survival rates (lx) of P marginatus adult is 100% at 27 days age and then starting to reduce After 44 days age, all female adult are died (Figure 3.12) In the above conditions, female adult of P marginatus starts laying egg at 22 days old The highest age specific fecundity (mx) is 39.267 at 15 The living time of each growing stage and whole life cycle of both male and female of P marginatus are significantly different when rearing at 25oC and 30oC, at P