RESEARCH ON BIOLOGY AND ECOLOGY OF THE CASSAVA MEALYBUG, Phenacoccus manihoti Matile-Ferrero, 1977 Homoptera: Pseudococcidae, ON CACSSAVA AND THEIR INTEGRATED MANAGEMENT Specializatio
Trang 1RESEARCH ON BIOLOGY AND ECOLOGY OF THE
CASSAVA MEALYBUG, Phenacoccus manihoti (Matile-Ferrero,
1977) (Homoptera: Pseudococcidae), ON CACSSAVA AND
THEIR INTEGRATED MANAGEMENT
Specialization: Plant Protection Code: 9.62.01.12
SUMMARY OF THESIS FOR THE DEGREE OF DOCTOR OF AGRICULTURE
Ha Noi - 2019
Trang 2The thesis was completed at Vietnam Academy of Agricultural
This thesis can be referred to at:
1 Vietnam National Library
2 Library of Vietnam Academy of Agricultural Sciences
3 Library of Plant Protection Institute
Trang 3INTRODUCTION
1 Rationale
The Cassava Mealybug, Phenacoccus manihoti (Homoptera:
Pseudococcidae), was firstly detected on cassava in 1960 in Africa It spreads with cassava at speed of 300 km/year and enters 31 out of 35 cassava production countries in this continent by 1987 (Herren,
1990; Neuenschwander et al., 1990) This pest can cause a loss of
84% of cassava productivity (Nwanze, 1982)
In Vietnam, the Cassava Mealybug was firstly found in July 2012
in Tay Ninh province To date, no researches have been conducted
on this pest in Viet Nam while its biology and ecology are scientific basis for defining effective measures for sustainable management is
urgently needed Therefore, the “Research on biology and ecology
of the Cassava Mealybug, Phenacoccus manihoti
(Matile-Ferrero, 1977) (Homoptera: Pseudococcidae), on cassava and their integrated management” is of great significance
2 Purpose and requirements of the thesis
2.1 Purpose
Determine the biological, ecological characteristics of P manihoti
and propose the control measures base on IPM for sustainable development of the cassava industry in Vietnam
2.2 Requirements
Recording the infestation of P manihoti on cassava-growing
provinces/regions in Vietnam Determine biological and ecological characteristics of the Cassava Mealybug in laboratory conditions; Determining the occurrence, annual a population dynamics and environmental factors that related to outbreak of this sucking insect
in cassava-growing areas of Vietnam Find out the feasible control
measures for P manihoti on cassava production
3 Scientific and practical significances of thesis
3.1 Scientific significances
Thesis provides scientific data on invasion, establishment of the Cassava Mealybug populations in cassava-growing areas in Vietnam
Providing new scientific data on biology and ecology of P manihoti
as foundation for control measures in Vietnam
Trang 43.2 Practical significances
Output of thesis as scientific foundation for IPM to control
cassava mealybug populations in cassava
4 Subject and scope of research
4.1 Research subject
The Cassava Mealybug, P manihoti damaging cassava plants
4.2 Scope of research
Thesis’s scientific data covered the invasive status, population
setup, biological and ecological characteristic of P manihoti
including life cycle, annual population density, ovipostion capacity
The effectiveness of on-going IPM on P manihoti –infesting region
in Vietnam (Tay Ninh, Dong Nai, Phu Yen, etc )
5 New contribution of dissertation
- Providing the update reports on invasion of the Cassava Mealybug in cassava-growing areas of Vietnam
- Proving the scientific data on life cycle, ecological characteristic
of P manihoti in Vietnam
- Providing the data on effectivenes of control measures including
using Anagyrus lopezi
6 Thesis structure
This dissertation comprises 156 pages with 36 tables and 31 figures allocated into introduction, main thesis contents (3 chapters), conclusion and proposals The thesis cited 114 references including 30 papers in Vietnamese and 84 papers in English
Chapter 1 LITERATURE REVIEW
1.1 Scientific base of thesis
The composition of cassava pests in each geographical growing region is very different The Cassava Mealybug, with highly reproductive capacity, rapid dispersal, are emerging as highly environment-adapting insect pest all over the cassava-growing areas
cassava-In order to control effectively this pest, understanding of biological, ecological, population dynamic as well as factors affecting the
density of the Cassava Mealybug on cassava are necessary for
building up IPM strategy in cassava plant protection
Trang 51.2 The status of cassava-cultivation in the world and Vietnam
Cassava is cultivated mostly at tropical and subtropical areas with more than 100 countries in Asia, Africa and America Cassava considered as the fifth food crop (252.20 million tons) after corn,
rice, wheat and potatoes (Nguyen Van Bo et al., 2013)
In Vietnam, cassava is one of the importance food crops after rice and corn The cassava-growing areas in the period of 2011-2015, reached 551.1 - 566.5 thousand ha, cassava productivity 176.4 - 188.4 quintals/ha
1.3 Research on the Cassava Mealybug in the world
1.3.1 Species composition of cassava insect pests
Cassava production is attacked by many insect pests, at South America nearly 200 species of arthropods are recorded (Bellotti, 1990) including 17 common pests on cassava (Bellotti and Schoonhove, 1999)
1.3.2 Research on the Cassava Mealybug
Species composition of mealybugs damaging cassava
According to Williams Granata de Willink (1992), 19 species of mealybugs (Pseudococcidae) have been discovered on cassava in the world The main Cassava Mealybugs have been studied in biology, ecology and measure of control
Taxonomy, origin, distribution, damage of the Cassava Mealybug
Cassava Mealybug, P manihoti belongs to the family of
Pseudococcidae (Homoptera) It originated in the tropics of the
Americas (Gutierrez et al., 1988; Löhn et al., 1990; )
In the 1970s, P manihoti accidentally introduced into western
Africa, then spread to most cassava growing countries in Africa By
2008, it entered Asia (FAO-IPM, 2013; Herren, 1990; Parsa et al.,
2012, Winotai et al., 2010)
P manihoti is the most dangerous pest on cassava Cassava root
yield could be reduced by 58-84% when severely damaged by
Cassava Mealybug (Bellotti et al., 1999; Nwanze, 1982; Sartiami et al., 2015; )
Trang 6Study on morphology of the Cassava Mealybug
The morphological characteristics of P manihoti at each development phases of life cycle have been described in Parsa et al
(2012) and some other authors
Research on biology of the Cassava Mealybug
Biological characteristics of P manihoti have been recoreded in publication of Barilli et al (2014), Le Rü and Fabres (1987), Nwanze (1978) and Parsa et al., (2012)
Study on ecological characteristics of the Cassava Mealybugs
The effects of food crops, climate, natural enemies on P manihoti populations have been refered in some publication of Barilli et al., (2014), Essien et al., (2013),
Study on control measures of the Cassava Mealybug
The cultivation, mechanical and biological methods to control P manihoti have been mentioned in many publications (Bennett and
Greathead, 1978; Emehute and Egwuatu, 1990; Nwanze, 1978; )
1.4 Study on the Cassava Mealybug, P manihoti, in Vietnam
1.4.1 Species composition of cassava insect pests
No cassava pests have been listed via some crops surveys of pests and diseases Six species of cassava pests were recorded in studies of
Nguyen Thi Chat et al., (2005), Pham Van Lam (2013), Plant
Protection Research Institute (1976, 1999a, 1999b),
1.4.2 Study on the Cassava Mealybug, P manihoti
Species composition of mealybugs on cassava in Vietnam
On cassava in Vietnam, two species of mealybug were identified
as Ferrisia virgata, Phenacoccus manihoti (Pham Van Lam, 2013)
Invasion and damage of the Cassava Mealybug in Vietnam
The Cassava Mealybug, P manihoti was first discovered in Tay
Ninh province in July 2012 on an area of 169 ha By 2013, 10
provinces have recorded infested by the Cassava Mealybug on
cassava with a total infected area of 1,350.037 ha (Plant Protection Department, 2013)
Study on morphological characteristics of CM
No publication on morphological characteristics of the Cassava Mealybug have been issueded yet
Trang 7Research on biological characteristics of the Cassava Mealybug
Some studies on the biological characteristics of the Cassava Mealybug were conducted at Hue University (Tran Dang Hoa,
Nguyen Thi Giang, 2014; Hoang Huu Tinh et al., 2018a, 2018b)
Study on ecological characteristics of the Cassava Mealybug
Ecological characteristics of the Cassava Mealybug were done at Hue University (Tran Dang Hoa, Nguyen Thi Giang, 2014; Hoang
Huu Tinh et al., 2018a, 2018b)
Study on measures to suppress the Cassava Mealybug
The Plant Protection Department has instructed some control measures to suppress the Cassava Mealybugs An initial study of
parasitic wasp Anagyrus lopezi was conducted (Hoang Huu Tinh et al., 2017)
Chapter 2 RESEARCH MATERIAL, CONTENT AND METHODOLOGY
2.1 Location and time of studies
2.1.1 Location
Laboratories at Provincial Plant Protection Sub Departments, Regional Plant Protection Center and Plant Protection Research Institute
Some main cassava-growing areas in Vietnam
Determine species composition of insect pests on cassava and the
invasive situation of Phenacoccus manihoti in Vietnam
Research on morphological, biological and ecological
characteristics of the Cassava Mealybugs, Phenacoccus manihoti, in
the laboratory
Trang 8Research on seasonal population dynamic and factors affecting
the density of the Cassava Mealybug on cassava in some cassava
growing area in Vietnam
Research measures trending sustainable IPM to control the
Cassava Mealybug, Phenacoccus manihoti
2.4 Methods
2.4.1 Determine species composition of pest of cassava and the invasive situation of P manihoti in Vietnam
Method of survey on species composition of pest of cassava
Base on the method of insect pest survey as described in publication of Plant Protection Research Institute (1997)
Methods to determine the invasive situation of the CM
According to the method of Plant Protection Research Institute (1997) and instruction described in QCVN 01-38: 2010/BNNPTNT issued by Ministry of Agriculture and Rural Development
Sample of P manihoti were handled according to Watson (2007) Identification of P manihoti followed by Williams (2004)
2.4.2 Methods of laboratory research on morphological, biological and ecological characteristics of the Cassava Mealybug
Maintained the Cassava Mealybug population in laboratory
Pumpkin (from the garden does not spray pesticides) at the beginning of ripening stage and cassava (KM 98-7 variety) is grown
in a plastic cup (25cm high, 15cm diameter) covered with net,
without pesticides used as food to feed P manihoti
P manihoti used in this study was collected in August-September
2015 in Quang Tri and Tay Ninh provinces
Study morphological characteristics
Description of shape, color, external structure, measurement of length/width and photograph of egg, nymphs, adult of the Cassava Mealybug under a microscope (number of samples observed for each phase/stage of development n = 30)
Research on biological and ecological characteristics of CM
P manihoti was kept in an ecological cabinet (RGX-400E brand)
at 20oC, 25oC, 30oC, 62% RH, 16L:8D Monitor time for each
development phases, life cycle, etc Life table parameters (rm, Ro, Tc,
Trang 9λ, DT) of P manihoti are calculated according to Birch (1948) and Kakde at el., (2014) The lower developmental threshold temperature
was determined according to Blunk (1923) and Sanderson (1917)
2.4.3 Research on seasonal population dynamic and factors affecting the density of the Cassava Mealybug on cassava in some cassava growing area in Vietnam
According to the method of Plant Protection Research Institute (1997) and instruction described in QCVN 01-38: 2010/BNNPTNT issued by Ministry of Agriculture and Rural Development
2.4.4 Research on measures trending sustainable IPM to control
the Cassava Mealybug, Phenacoccus manihoti
Manual control measures
Compare the level of P manihoti infestation, cassava yield
between control (no treatment) and manual-applying treatments
which mainly rely on removing P manihoti- infesting shoot
Evaluate the effectiveness of chemical combined with manual control
Compare the level of P manihoti infestation, cassava yield
between chemical spraying and combination of manual and chemical treatments
Research on application of Anagyrus lopezi
Compare the rate parasitism of wasp A lopezi on P manihoti in
wasps-releasing regions and control (non- wasp releasing regions)
2.5 Data analysis
Experimental data are processed by Excel software and statistical software of Statistix window, IRRISTAT
CHAPTER 3 RESEARCH RESULTS AND DISCUSSION
3.1 Cassava pests, invasion and hamful status of the Cassava
Mealybug, Phenacoccus manihoti, in Vietnam
3.1.1 Species composition of cassava pests in Vietnam
10 species of insects and miters were recorded on cassava in the study areas The Cassava Mealybug, Papaya Mealybug and Two Spotted Red Mites were highlighted as key pests In this study, 4
Trang 10insect species have added into the list of cassava pests of Viet Nam
which including termite Coptotermes sp., whitefly Aleurodicus disperses, common armyworm Spodoptera litura and cotton bollworm Helicoverpa armigera Base on updated information, the
12 species have been recorded in the list of cassava pests in Vietnam
3.1.2 The invasion status of the Cassava Mealybug (P manihoti)
in Vietnam
Invasive progress of the Cassava Mealybug in Vietnam
The Cassava Mealybug was first discovered in Vietnam in 2012
By 2017, it has appeared in 53 cassava growing districts of 16 provinces especially Tay Ninh, Dong Nai and Phu Yen provinces have many invaded-districts (7-8 districts) (Table 3.3)
Table 3.3 Occurrence of the Pink Cassava Mealybug at
cassava-growing regions in Vietnam by 2017
occurrence of P manihoti
Appearance year
Thanh, Duong Minh Chau, Hoa Thanh, Go Dau, Ben Cau, Tp
Tay Ninh
2012
2 Dong Nai Nhon Trach, Xuan Loc, Long
Khanh, Long Thanh, Đinh Quan, Tan Phu, Trang Bom and Vinh Cuu
Lam, Thanh Khe and Thanh Chuong
2013
9 Quang Tri Huong Hoa, Vinh Linh, Gio
Linh, Hai Lang and Cam Lo
2013
Trang 1110 Gia Lai Krôngpa, Ayunpa and Phu
Thien
2013
Đong Xuan, Song Hinh, Phu Hoa, Song Cau
2014
14 Binh Duong Tan Uyen, Bac Tan Uyen, Ben
Cat, Bau Bang and Dau Tieng
2014
Infesting route of cassava mealybugs in Vietnam
Cassava cuttings recorded as main pathway for the Cassava Mealybug The mealybug infesting cassava in provinces of Thanh Hoa, Nghe An, Quang Tri, Tay Ninh, …etc mostly take infesting cuttings from non-quota import channels from Cambodia and Laos
3.1.3 Damage of the Cassava Mealybug, P manihoti, in Vietnam
With mildly-infected of P manihoti, the cassava plants become
stunted, low dwarf, leaf deforms, shortening in stem and shoot, no young leaves can generate and reduction in yield of cassava roots In heavy-infested plant, leaves become yellow, dry, fall, whole tree dead easly
3.2 The morphological, biological, ecological characteristics of the
Cassava Mealybug, P Manihoti, in laboratory
3.2.1 The morphology
Adult females of the Cassava Mealybug are ovoid, rose-pink and dusted with white, powdery wax Body segments bear very short lateral and caudal white wax filaments The last segment has longest wax filaments and fully-developing adult female reached 2.2mm in length and 0.89mm in width
Eggs are oval shape with length of 0.45mm and breadth of 0.18mm, golden yellow and enclosed in woolly ovisacs located at the posterior end of the adult females
Nymphs in pink covered with powdery wax Body length and breadth measurements are, respectively, 0.52mm and 0.25mm for
Trang 12first instars/crawlers; 0.86mm and 0.41mm for second instars; 1.27mm and 0.51mm for third instars
3.2.2 The biological and ecological characteristics
Habitat
The Cassava Mealybug mainly lives on the underside of cassava leaves (60% of individuals) while others (30%) located in growing shoot of plant
The first nymphal instar of mealybug move actively where as later instars (the second and third) rarely dispersed from their location The adult lays eggs at the growing parts, the lower surface
of young cassava leaves, sometime in petioles at cassava shoot
Developing time and life cycle
Nymphs of the Cassava Mealybug develop throughout 3 instars The first instar takes longest time from 6.32 to 17.92 days The second instar is the shortest, from 4.70 to 12.26 days and the third instar take 5.08 to 13.87 days Time for each instar of nymphas at different temperatures were shown in Table 3.5 with significant
confidence (P <0.05)
Table 3.5 Developing time of P manihoti nymphs in laboratory
(in Plant Protection Research Institute, 2015) Nymphal
instar
Time for developments (days) at experimental conditions
Variat ion (days)
Average (days)
Variati
on (days)
Average (days)
Variat ion (days)
Average (days) The 1st instar 13-22 17.92±0.29 a 8-14 9.37±0.25 b 4-9 6.32±0.14 cThe 2nd instar 9-18 12.26±0.28 a 5-9 6.89±0.15 b 3-9 4.70±0.19 cThe 3rd instar 9-18 13.87±0.20 a 6-10 7.50±0.20 b 3-9 5.08±0.23 c
Note: n=30; letters in same column showed the significance difference of P<0,05
Nymphs of the Cassava Mealybug take longest time for development (16.11 - 44.05 days) in compared to other phases In comparison with pre-oviposition, duration of egg is shorter at 20oC, but is similarly at 25oC, 30oC Duration of egg and pre-oviposition were, respectively, 17.05 and 18.58 days at 25oC, 8.76 and 8.56 days
at 25oC, and 5.89 and 5.57 days at 30oC The life cycle of the Cassava Mealybug in this study lasts from 27.57 days to 79.68 days Developmental time of phases, life cycle of CM in the experiment
Trang 13(respectively) are different at a statistically significant level with a confidence level of P <0.05 (Table 3.6)
Table 3.6 Duration of immature stages and life cycle of P
manihoti in laboratory (in Plant Protection Research Institute, 2015)
Variat ion (days)
Average (days)
Variat ion (days)
Average (days)
Variat ion (days)
Average (days)
Pre-oviposition 15-20 18.58±0.29a 8-15 8.56±0.29b 4-9 5,57±0.22cLife cycle 71-86 79.68±0.48a 36-46 41.08±0.39b 20-35 27.57±0.45c
Note: n=30; different letters shown the significant diffirence of P<0.05
In our study, at 25oC, time for development of eggs, nymphs, time for development from egg to adult of the Cassava Mealybug were (respectively) shorter than those at the same temperature in publication of Dang Hoa, Nguyen Thi Giang (2014) But at 25oC in this study, duration of egg, nymphs, pre-oviposition, life cycle of the Cassava Mealybug were (respectively) significant longer than those
in research of Barilli et al., (2014) At 30oC, our data on duration of
egg, nymphs, life cycle was similar to that of Essien et al., (2013) but
slightly longer than those in pulicaton of Le Rü and Fabres (1987)
Rate of egg laying and longevity of the Cassava Mealybug
At 20oC and 25oC, female of the Cassava Mealybug has a similar oviposition period, with average of 28.67 and 28.89 days At 30oC, this figure is shortened to 17.06 days (Table 3.7)
Table 3.7 Rate of egg laying of P manihoti in different
temperature condition (in Plant Protection Research Institute, 2015)
Parameters Parameter value at different experimental condition
Variation
(days)
Average (days)
Variation (days)
Average (days) Variation Average
(days) Oviposition