Nghiên cứu đặc điểm sinh vật học, sinh thái học của rệp sáp bột hồng phenacoccus manihoti (matile ferrero, 1977) (homopter pseudococcidaehại sắn và biện pháp quản lý theo hướng tổng hợp tt tiếng anh

MINISTRY OF EDUCATION
MINISTRY OF AGRICULTURE AND
AND TRAINING
RURAL DEVELOPMENT
VIETNAM ACADEMY OF AGRICULTURE SCIENCES
-------------------------------

DO HONG KHANH

RESEARCH 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


The thesis was completed at Vietnam Academy of Agricultural
Sciences (VAAS).

Scientific Supervisor: Prof. Dr. Pham Van Lam

Critic Commentator 1: …………………………………………..

Critic Commentator 2: …………………………………………..

Critic Commentator 3:……………………………………………

The dissertation will be protected at Council for Thesis Assessment
before the Institute of Dissertation Boads meets at Institute level, held
at Viet Nam Academy of Agricutural Sciences
At 8 hours 30’, date….monh…..year 2019

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


INTRODUCTION
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 (MatileFerrero, 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.
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3.2. 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 cassavagrowing 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.
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.
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1.2. 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;...).

3


Study 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.
4


Research 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.
2.1.2. Time of studies
Time of studies from 2014 to 2017.
2.2. Research materials
Cassava varieties, tools, chemicals, equipment for rearing cassava
mealybugs in the laboratory and conducting field experiments.
2.3. Study contents
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.

5


Research 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,
6


λ, 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
7

insect 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 cassavagrowing regions in Vietnam by 2017
No

Provinces

1

Tay Ninh

2

Dong Nai

3
4
5

6
7
8

Long An
Ba Ria-Vung
Tau
Hau Giang
Son La
Thanh Hoa
Nghe An

9

Quang Tri

Districts recorded the
occurrence of P. manihoti
Tan Chau, Tan Bien, Chau
Thanh, Duong Minh Chau, Hoa
Thanh, Go Dau, Ben Cau, Tp.
Tay Ninh
Nhon Trach, Xuan Loc, Long
Khanh, Long Thanh, Đinh
Quan, Tan Phu, Trang Bom and
Vinh Cuu
Đuc Hoa
Son Moc, Chau Đuc, Tan
Thanh, Xuyen Moc and Đat Đo
Chau Thanh

Mai Son
Nhu Xuan
Thanh Ngoc, Thanh My, Thanh
Lam, Thanh Khe and Thanh
Chuong
Huong Hoa, Vinh Linh, Gio
Linh, Hai Lang and Cam Lo

8

Appearance year
2012

2013

2013
2013
2013
2013
2013
2013

2013


10

Gia Lai

11

12
13

Kon Tum
Dak Lak
Phu Yen

14

Binh Duong

15
16

Ninh Thuan
Binh Dinh

Krôngpa, Ayunpa and Phu
Thien
Uban of Kon Tum
Krông Bông
Tuy An, Tay Hoa, Son Hoa,
Đong Xuan, Song Hinh, Phu
Hoa, Song Cau
Tan Uyen, Bac Tan Uyen, Ben
Cat, Bau Bang and Dau Tieng
Ninh Sơn
Vinh Thanh

2013

2014
2014
2014

2014
2014
2015

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

9


first 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

The 1st instar

The 2nd instar
The 3rd instar

Time for developments (days) at experimental conditions
20 C, 62% RH
25oC, 62% RH
30oC, 62% RH
Variat
Average
Variati
Average
Variat
Average
ion
(days)
on
(days)
ion
(days)
(days)
(days)
(days)
13-22 17.92±0.29 a
8-14
9.37±0.25 b
4-9
6.32±0.14 c
a
b
9-18

12.26±0.28
5-9
6.89±0.15
3-9
4.70±0.19 c
a
b
9-18
13.87±0.20
6-10
7.50±0.20
3-9
5.08±0.23 c
o

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

10


(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)
Phase

Egg
Nympha
Pre-oviposition
Life cycle

Developing time (days) at different condition
20oC, 62% RH
25oC, 62% RH
30oC, 62% RH
Variat
Average
Variat
Average
Variat
Average
ion
(days)
ion
(days)
ion
(days)
(days)
(days)
(days)
16-18 17.05±0.08a

8-9
8.76±0.17b
5-7
5.89±0.08c
a
b
36-51 44.05±0.46
21-27 23.76±0.28
11-22 16.11±0.34c
a
b
15-20 18.58±0.29
8-15
8.56±0.29
4-9
5,57±0.22c
a
b
71-86 79.68±0.48
36-46 41.08±0.39
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

20oC, 62% RH
Oviposition
period (days)
Rate of eeg
laying
(eggs/female)

25oC, 62% RH

30oC, 62% RH

Variation
(days)
15-41

Average
(days)
28.67±1.00a

Variation
(days)
15-41

Average (days)

Variation

28.89±1.21a

11-21

Average
(days)
17.06±0.52b

309-584

440.13±84.38a

316-618

458.38±23.44a

132-387

252.0±77.6b

Note: Different letter indicated the significance differences by P < 0.05.

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Rate of egg laying of Phenacoccus manihoti female ranged from
132 to 618 eggs. At temperatures of 20oC and 25oC, a female of the
Cassava Mealybugs laid 440.13 - 458.38 eggs/female, 1.8 times
higher than those at 30oC (252.0 eggs/female).
Average daily egg laid per female of the Cassava Mealybug
varied depending on temperature. Average daily egg laid per female
reached the pick at beginning, sharply droped and oviposition period
was the most short at 30oC. At 20oC and 25oC, the pick of average
daily egg laid per female was latter and oviposition period was
longer (Figure 3.13).

Fig. 3.13. Average daily egg laid per female of the Cassava
Mealybug at different temperatures (in Plant Protection Research
Institute, 2015)
Female longevity average of 22.06 - 48.06 days. At 30oC, average
of living time was 44.0 days, whereas at 20oC, this figure extends up
to 107.89 days. Experimental data collected from raising-temperature
treatments (from 20oC to 30oC) showed 2.2 times reduction of female
longevity as well as 2.5 times reduction of living-time (Table 3.9).
Table 3.9. The living-time of Phenacoccus manihoti in laboratory
(in Plant Protection Research Institute, 2015)
Parameters

Female longivirty
(days)
Living time (days)

Experimental temperatures
25oC, 62% RH
Variati
Average
on
(days)
48.06±2.28a
23-50
38.53±1.27 b

20oC, 62% RH
Variation
Average
(days)
36-56

30oC, 62% RH
Variati
Average
on
(days)
15-27
22.06±0.59
c

96-112
107.89±1.51 a
53-80
70.74±1.33 b

37-50
44.0±0.68 c
Note: Different letter indicated the significance differences by P<0.05.

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The lower developmental threshold temperature and number of
generations/year
The lower developmental threshold temperture of the Cassava
Mealybug was 14.8oC, similar to findings of various studies abroad
(CABI, 2005; Iheagwam, 1981; Le Rü and Fabres, 1987; Lema and
Herren, 1985; Nwanze et al., 1979). Based on monthly temperature
in Tay Ninh and Phu Yen in the study years (2014-2017), the
theoretical number of generations per year were calculated and were
11.1-11.7 and 10.7-11.4 respectively in the two provinces.
Life table of the Cassava Mealybug
Survivals at pre-mature of the Cassava Mealybug in laboratory
At the temperature of 25oC and 30oC, the Cassava Mealybug had
very high survival rates at pre-mature stages, and was 94.28% and
94.67%, respectively. At 20oC, the survival rate was considerably
lower, was only 86.96%.
Age specific survival rates (lx), age specific fecundity (mx) of the
Cassava Mealybug at 20ºC and 62% RH
On the 97th day, age specific survival rate (lx) was 100%. From
the 98th day, female adults start to die but age specific survival rate
remains relatively high (81%) until the 108th day from when the
survival rate (lx) drop sharply and on the 119th day, all individuals
die (Figure 3.14).

Figure 3.14. Age specific survival rate (lx), age specific fecundity
(mx) of the Pink Cassava Mealybug at 20ºC and 62% RH
In the above testing conditions, females started to lay eggs from
the 81st day. They had the best age specific fecundity (mx) between
the 85th and 89th day (mx = 18.5 – 22.06). After that, their age
13


specific fecundity (mx) declined and from the 113th day their age
specific fecundity dropped sharply. From the 119th day, they stopped
laying eggs. Their fecundity (mx) was 523.57 eggs.
Age specific survival rates (lx) and age specific fecundity (mx) of
pink malybug at temperature of 25ºC and humidity of 62%
Age specific survival rate (lx) was 100% until the 40th day. From
the 41st day, females started to die but their age specific survival rate
(lx) remained high. From the 68th day, age specific survival rate (lx)
dropped a lot. On the 78th day, all females die (Figure 3.15).

Figure 3.15. Age specific survival rate (lx), age specific fecundity
(mx) of the Cassava Pink Mealybug at 25ºC and 62% RH
In the above testing conditions, females started to lay eggs from
the 41st day. They had the best age specific fecundity (mx) on the 44th
day (mx = 24.07). After that, their age specific fecundity (mx)
declined gradually and from the 53th day their age specific fecundity
dropped sharply. From the 78th day, they stopped laying eggs. Their
fecundity (mx) was 545.98 egg, higher than that at 20ºC.
Age specific survival rates (lx), age specific fecundity (mx) of the
Cassava Mealybug at 30ºC and 62% RH
Age specific survival rate (lx) was 100% until the 37th day. From
the 38th day, females started to die but their age specific survival rate

(lx) remained high. From the 41st day, age specific survival rate (lx)
dropped a lot. On the 48th day, all females die (Figure 3.16).
In the above testing conditions, females started to lay eggs from
the 27th day when they had the best (mx). After that, their age specific
fecundity (mx) declined gradually but remained high (20.25 - 26.79).
14


From the 37th day their age specific fecundity (mx) dropped sharply.
From the 48th day, they stopped laying eggs. Their fecundity (mx)
was 308.06 eggs, higher than that at 20ºC and 25ºC.

Figure 3.16. Age specific survival rate (lx), age specific fecundity
(mx) of the Cassava Mealybug at 30ºC and 62% RH
The fecundity (mx) of females in this research is higher than the
fecundity indicated in foreign researches (Barilli et al., 2014; Essien
et al., 2013; Leuschner, 1978;…).
In other words, the increase of temperature from 20oC to 30oC
leads to a considerable reduction of the period in which females have
high age specific survival rate. The fecundity (mx) of females is the
highest at the temperature of 25oC and the lowest at 30oC.
Population growth paramanters of the Cassava Mealybug
The increase of temperature from 20oC to 30oC results in a rise of
intrinsic rate of increase (rm) and finite rate of increase (λ), but also
results in shorter period of a generation when delivering off-springs
(Tc) and shorter period to double the number of individuals in a
population (DT). The net increase rate (Ro) of a generation increases
when the temperature rises from 20oC to 25oC, but reduces
remarkably when the temperature rises to 30oC (Table 3.15). The
variability of these indicators is similar to the variability of the

corresponding indicators in the research by Le Rü and Fabres (1987).
In this research, values of live table parameters Ro, rm, λ are
considerably lower while Tc, DT values are obviously higher than
some foreign researches (Barilli et al., 2014; Iheagwam, 1981; Le Ru
and Fabres, 1987;…).
15


Table 3.15. Population growth parameters of the Cassava
Mealybug at various constant temperatures (in Plant Protection
Research Institute, 2015)
Testing
temperature (ºC)
20
25
30

Ro
455.57
476.29
290.66

Values of parameters
rm
λ
Tc
0.065
1.07
94.45
0.110

1.12
56.13
0.164
1.18
34.58

DT
10.70
6.31
4.23

Note: Humidity 62%, 16L:8D, feed: leaves of cassava KM 98-7

Host plants of the Cassava Mealybug Phenacoccus manihoti
The research does not detect the presence of the Cassava
Mealybug on on jackfruit, pineapple, goat weed and rubber plants
around cassava fields. It is found on rubber plants in Thailand.
3.3. Seasonal population dynamic and factors affecting the density
of the Cassava Mealybug P. manihoti on cassava in some cassava
growing areas in Vietnam
3.3.1. Seasonal population dynamic of the Cassava mealybug
Seasonal population dynamic in Phu Yen province
The survey in Dong Xuan district (2015) and Son Hoa district
(2016) shows that the Cassava Mealybug appear and damage all
growth stages of cassava plants, but cause the most damage in
formation and development stages of bulb (Figure 3.18, Figure 3.19).

Figure 3.18. Seasonal population dynamic of the Cassava Mealybug
in Dong Xuan district (Phu Yen province, 2015)

Figure 3.19. Seasonal population dynamic of the Cassava Mealybug
in Son Hoa district (Phu Yen province, 2015)
16


3.3.2. Factors affecting the density of P. manihoti on cassava
Climate factors
In Dong Xuan and Son Hoa districts of Phu Yen province, the
Cassava Mealybug infested with high density in sunny, hot and dry
conditions (low humidity, the lowest rainfall in the years)
Cultivation factors
The research in Tay Ninh province shows that the Cassava
Mealybug infested during the whole year on cassava plants. Its
density and the percentage of plant tops affected in the monoculture
fields (one crop cycle of cassava/year) were always higher than those
recorded in the polyculture fields (2 crop cycles/year) (Figure 3.22).
Figure 3.22. Seasonal population dynamic of the Cassava
Mealybug in Tay Ninh province in 2013-2015
3.4. Measures trending sustainable integrated management to
control the Cassava Mealybug, P. manihoti, in the reaserch area
3.4.1. Quarantine measures
The research findings confirm that cassava cuttings infested with
the Cassava Mealybug are the main pathway (Section 3.1.2.2).
Therefore, quarantine is an effective way to prevent the continuing

spread of the Cassava Mealybug.
3.4.2. Cultivation and manual measures
Use of pest-free cuttings
To ban the cuttings infested with the Casava Mealybug for
propagation purpose is of great importance to prevent the increasing

spread of the Casava Mealybug. Infested cuttings can be treated by
soaking in detergent solution or pesticides.

17


Manual measures
In Dong Xuan district and Song Hinh district (Phu Yen province),
affected plants tops were cut and destroyed. Before the test, the
percentage of infested plant tops in all experiments were relatively
high (46.6-53.3% in Dong Xuan district, 31.2-42.1% in Song Hinh
district) and their infestation was at grade 3. However, on the 28 th
day after cutting the plant tops, the percentage of infested plant tops
in the top-removing experiment was very low (only 13.4% in Dong
Xuan and 27.1% in Song Hinh) and their infestation was at grade 1.
Whereas, the control (no top cutting) had high or very high
percentage of infested plant tops (80% in Dong Xuan and 60.1% in
Song Hinh), at grade 3. These figures show that the top-removing
measure in Dong Xuan is more effective than that in Song Hinh. The
bulb yield in the top-removing experiments was higher than the
control without top-removing (was 26.4 tons/ha and 21.0 tons/ha,
respectively, in Dong Xuan; was 25.3 tons/ha and 18.8 tons/ha,
respectively, in Song Hinh).
3.4.3. Combination of chemical measure and manual measure
The removal and destruction of affected plant tops are not always
highly effective in preventing the Cassava Mealybug. In order to
raise the effectiveness of this measure, chemical pesticides are also
applied. This experiment was conducted in Dong Xuan and Song
Hinh district (Phu Yen province).
Before experiments, the percentage of infested plant tops was

relatively high in all experiments, namely 46.6-66.6% in Dong Xuan
and 31.2-38.4% in Song Hinh, at grade 3. However, on the 28th day
after treatment, treatment 1 (removal and destruction of affected
plant tops, combined with a spray of Actara 25WG) had the
percentage of infested plant tops of only 6.7% in Dong Xuan and
22.5% in Song Hinh, grade 1; treatment 2 (a spray of Actara 25WG)
had the percentage of infested plant tops of 60% and 28.3% in Dong
Xuan and Song Hinh, respectively. Whereas, the control treatment
(no removal and destruction of affected plant tops, no pesticides) had
the highest percentage of infested plant tops, 80% in Dong Xuan and
60.1% in Song Hinh, both at grade 3. The yield harvested in
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treatment 1 and treatment 2 are higher that obtained in the control.
3.4.4. Conservation and utilization of natural enemies
Conservation and enhancement of natural enemies
Species composition of natural enemies on cassava plants in the
study area
In implementing the research, 6 natural enemies were found in the
Cassava Mealybug populations in in the study provinces (Tay Ninh
and Phu Yen) (Table 3.27).
Table 3.27. List of natural enemies on cassva in Tay Ninh and
Phu Yen in 2014 -2015
No
1
2
3
4
5

6

Common
name
Six spotted
ladybird
Red lady beetle
Lady beetle
Green
Lacewing
Parasitoid
Parasitoid

Scientific name

Order, family

Menochilus sexmaculata
(Fabricius)
Micraspis discolor
(Fabricius)
Nephus sp.
Plesiochrysa ramburi
(Schneider)
Anagyrus lopezi (De Santis)
Acerophagus sp.

Coleoptera, Coccinellidae
Coleoptera, Coccinellidae
Coleoptera, Coccinellidae

Neuroptera, Chrysopidae
Hymenoptera, Encyrtidae
Hymenoptera, Encyrtidae

Most (5 out of 6 species) of the recorded natural enemies are
native to the investigated areas and are polyphagous and not specific
on the Cassava Mealybug. Only wasp Anagyrus lopezi is specific and
not native. This species has entered Vietnam together with the
Casava Mealybug, except for some areas in Tay Ninh (Phan
commune, Duong Minh Chau district; Thanh Dien, An Binh, Ninh
Dien and Hao Duoc communes, Chau Thanh district; Binh Minh
commune in Tay Ninh city) where the wasp Anagyrus lopezi was
imported from Thailand.
Role of wasp A. lopezi in keeping down population of CM in nature
During March-May 2014, a survey for the rate of parasitism of
wasp Anagyrus lopezi was conducted in Tay Ninh, Dong Nai and Ba
Ria-Vung Tau. The survey sites were not released A. lopezi by the
IPM-FAO program.
The survey shows that the Cassava Mealybug in cassava fields in
Tay Ninh was parasited by Anagyrus lopezi at high rate (47.3% on
average). In the surveyed fields in Dong Nai, Ba Ria-Vung Tau, the
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Cassava Mealybug was parasited by Anagyrus lopezi at considerably
lower rate (9.3% and 22.8%, respectively) (Figure 3.24).
In Phu Yen province, wasp Anagyrus lopezi was found on the
Cassava Mealybug in February-July 2016 in Dong Xuan district,
where 10-90% of the samples were parasited. In the cassava fields in
Phu Hoa district, a monitoring was conducted between February and

September 2016 and recorded the rate of parasitism of A. lopezi on
the Cassava Mealybug samples collected between 15 April and 10
June 2016. Especially, the highest rate of parasitism of A. lopezi on
the Cassava Mealybug was recorded on 13 May 2016 (10-40%). In
summary, wasp A. lopezi has a certain role in keeping down
population of the Cassava Mealybug. And, therefore, this useful role
must be protected and enhanced.

Figure 3.24. The rate of parasitism of wasp A. lopezi on the Cassava
Mealybug and the rate of cassava plant tops infested with the
Cassava Mealybug in some Southeastern provinces (3 - 5/2014)
Preliminary results of releasing wasp A. lopezi to suppress the
Cassava Mealybug
In 2014, wasps A. lopezi were released in Phan commune (Duong
Minh Chau district), Thanh Dien and An Binh communes (Chau
Thanh district) in Tay Ninh. Before releasing wasp A. lopezi, the rate
of parasitism on the Cassava Mealybugs in the experiment fields was
very low (only 7.2 - 9.4%). On the 60th day after the wasp release,
this rate reached the peak (83.1 - 92.5% on average) while the
control fields (no wasps were released) had the lowest rate of
parasitism of the Cassava Mealybugs, was 7.2-12.4% (Fig. 3.25).

20


Figure 3.25. The rate of parasitism on the Cassava Mealybug in
the A. lopezi-released fields (Tay Ninh, 2014)

Figure 3.26. The rate of parasitism on the Cassava Mealybug in
the A. lopezi-released fields (Tay Ninh, 2015)

In 2015, the pilot release of wasp A. lopezi was implemented in
such communes as Ninh Dien, Hao Duoc (Chau Thanh district) and
Binh Minh (Tay Ninh city). The rate of parasitism on the Cassava
Mealybug in the A. lopezi-released fields was similar to the rate
recorded in 2014. Before the wasps were released, the rate of
parasitism was 12.1 - 43.5%. After the wasps were released, the rate
of parasitism rose gradually and reached the peak on the 60th day
(84.5 - 92%). The fields where no wasps were released had lower
rate of parasitism, only 12.1 - 18.2% (Figure 3.26).
3.4.5. Proposed practices to control the Cassava Mealybug
Phenacoccus manihoti in Vietnam
* Quarantine measure
To prevent the transport of affected cassava cuttings from
Cambodia and Laos to Vietnam and from affected areas to nonaffected areas in Vietnam.
* Manual and cultivation measures
21


- To destroy completely remains of affected cassava plants, the
plants and weed in cassava fields, which are shelters of the Cassava
Mealybug.
- To use cassava cuttings free from the Cassava Mealybug, use no
cassava cuttings from the infested areas.
- To ensure watering, especially during dry seasons.
- To check regularly cassava fields, eliminate weed and plants
which are supplementary feed and shelters for the Cassava
Mealybug. Once the Cassava Mealybugs are detected, all the
plants/parts of plants affected must be removed and destroyed.
- To have rotational farming of cassava and other crops which are
not supplementary feed for the Cassava Mealybug, if possible, in

order to mitigate the ocurrence of this pest.
* Biological measure
- To protect and enhance natural enemies available in cassava
fields, especially wasp A. lopezi. To apply no chemical insecticides
in the areas where wasps A. lopezi have been released.
- To organize mass-production and release of A. lopezi in cassava
fields in order to keep down population of the Cassava Mealybug.
* Chemical measure in combination with top-removing measure
To use chemical pesticides in combination with removal and
destruction of affected cassava plant tops. To apply pesticides in
accordance with Four-Right principle.
CONCLUSION AND RECOMMENDATION
1. Conclusion
1.1. Ten harmful insects have been recorded on cassava in
Vietnam, in this study of with the addition of 4 species (Coptotermes
sp., Aleurodicus dispersus, Spodoptera litura, Helicoverpa
armigera). Among them, the Cassava Mealybug, Papaya Mealybug
and Two Spotted Red Mites are major pests of cassava. Particularly,
the Cassava Mealybug is an invasive pest which spread and damaged
cassava in 53 districts of 16 provinces in Vietnam in 2017.

22


1.2. At constant conditions (20oC, 25oC, 30oC; 62% RH and
16L:8D) and leaves of cassava KM 98-7 as food, female nymphal
has 3 instar. The average life cyle of the Cassava Mealybug is 27.5779.68 days. The Cassava Mealybug reproduces by parthenogenesis.
The fecundity of females is 252.0-458.38 eggs/female. Females can
live for 22.06-48.06 days. The temperature increase from 20oC to
30oC shortens the time period of a generation, female longevity,

Living time, oviposition, and reduces fecundity of females. The lower
developmental threshold temperatures of egg, nymph, preoviposition and whole life cycle were 14.7oC, 14.5oC, 15.7oC and
14.8oC. Theoritically, the Cassava Mealybug can complete about
11.1-11.7 and 10.7-11.4 generations per year in Tay Ninh and Phu
Yen, respectively.
1.3. Under laboratory conditions, the Cassava Mealybug had
higher survival rate of all development stages (ranged from 93.48100%). When temperature increased from 20oC to 30oC resulted in
the intrinsic rate of natural increase (rm) and finite rate of increase
(λ), but shortened the mean generation time (Tc) and doubling time
(DT). The net reproductive rate (Ro) increased when temperature
increased from 20oC to 25oC, but decreased rather signigicantly
when the temperature is raised to 30oC. Obtained results show that
the values of Ro, rm, λ (were 290.66-476.29, 0.065-0.164, 1.07-1.18,
respectively) were significantly lower, but the values of Tc, DT (were
34.58-94.45, 4.23-10.7, respectively) were higher those documented.
1.4. Although the Cassava Mealybug have spread to 16 provinces
in Vietnam, they have caused more damages in Tay Ninh, Dong Nai
and Phu Yen. It occurs during the whole year but more at period
when has high temperature (35oC - 40oC) and dry weather.
1.5. To plant cassava cuttings free from the Cassava Mealybug,
remove and destroy the affected plant tops can prevent the Cassava
Mealybug. Wasps Anagyrus lopezi can keep down population of the
Cassava Mealybug on cassava in Vietnam. This wasp species can
23