plant diseases transmitted through vectors

1. ASSIGNMENT ON
INSECT VECTOR TRANSMITTED DISEASES AND THEIR
MANAGEMENT
ENT 623
PESTS OF CROPS AND THEIR MANAGEMENT (1+1)

2. Vector & Insect Vector
• A vector is an agent that carries and transmits infectious pathogen from
one organism to another living organism
• Insect vector- Insects that are responsible for the spread of Plant Diseases,
they transmit below the pathogens which cause plant diseases.
 Virus
 Bacteria
 Fungus
 Phytoplasma

3. 48%
9%
4%
11%
24%
4%
Viral Diseases:An Overview
Bacteria Fungus Nematodes Mycoplasmas Virus Protozoa
53%
23%
13%
11%
Insect Transmitted
Nematode Transmitted
Mechanically Transmitted
Transmitted by Arachanids
Data Source -Diseases:An Emerging Threat to Human,Animal and plant Health: Workshop Summary, 2011

4. Mode of virus transmission

5. Nonpersistent virus transmission
• Is characterized by very short acquisition and inoculation times of seconds to
minutes
• Only transmission of RNA Virus
• Historically, this was referred to as ‘stylet-borne’- it was thought that virus was
merely contaminating the outside of the stylet
Semipersistent virus transmission
• Acquisition can occur within minutes, but the efficiency increases with prolonged
feeding and retention period is of hours to days.
Eg: Caulimoviruses, Closteroviruses
• Transmission of RNA and DNA genomes.

6. Green leafhopper: Nephotettix virescens
(Cicadellidae: Hemiptera)
Rice Tungro Virus, Rice Yellow Dwarf And
Transitory Yellowing Diseases
Symptom
 Both nymphs and adults desap the leaves and cause Yellowing of leaves
from tip to downwards is the typical symptom
 Discoloration begins from leaf tip and extends down to the blade or the
lower leaf portion
 Disease complex is associated with rice (RTBV) (RTSV)
Management
Use resistant varieties like IR 20, IR 50, CR 1009, Co 46
Nursery should not be raised near the lamp posts.
chemical spray
1. Buprofezin 25 SC 800 ml or
2. Imidacloprid 17.8 SL 100 -125 ml
ETL 2 Nos. / hill - Tungro endemic area

7. Brown plant hopper: Nilaparvata lugens
(Delphacidae: Hemiptera)
Vector Of Grassy Stunt, Ragged Stunt And
Wilted Stunt Diseases
Symptoms
 Nymphs and adults congregate at the base of the plant above the water
level and suck the sap from the tillers.
 The affected plant dries up and gives a scorched appearance called
“hopper burn”
 Circular patches of drying and lodging of matured plants are typical
symptoms caused by this pest
ETL: 8-10 Nos./hill or 20 Nos./hill when spider is present at
1 No./hill
 Use resistant varieties like Co 42, Co 46
 Release of natural enemies like wolf spider, Lycosa pseudoannulata
and green mirid bug Cyrtorrhinus lividipennis.
 Avoid close planting and provide 30 cm rogue spacing at every
2.5 m to reduce the pest incidence.
 Avoid use of excessive nitrogenous fertilizers.

8. Bean aphid: Aphis craccivora (Aphididae:
Hemiptera)
Vector of Groundnut rosette assistor virus
(GRAV)
Symptoms
 The affected plants appearance of dense clump or dwarf shoots with tuft
of small leaves forming in a rosette fashion. The plant exhibits chlorosis and
mosaic mottling.
 The infected plants remain stunted and produce flowers, but only a few
of the pegs may develop further to nuts but no seed formation.
 Sometimes honey dew deposited.
Management
 Release predator, Chrysoperla carnea grubs @ 5000 / ha.
 Use entomopathogenic fungus Fusarium pallidoroseum or
Beauveria bassiana to cause epizootics in aphids in the cowpea field
 Spray the infested crop with methyl demeton 25 EC 500 ml or
Imidacloprid 17.8 SL 100 -125 ml in 700 L of water per ha.

9. Leaf hopper: Orosius albicinctus (Cicadallidae:
Hemiptera)
Act as vector for Phyllody – Phytoplasma
Symptoms
 The symptoms starts with vein clearing of leaves .The disease manifests itself
mostly during flowering stage, when the floral parts are transformed into green
leafy structures, which grow profusely.
 The flower is rendered sterile. The veins of phylloid structure are thick and
prominent.
 The plant is stunted with reduced internodes and abnormal branching

10. Red gram sterility mite: Aceria cajani
(Eriophyidae : Acari) NON-INSECT
Vector for pigeon pea sterility mosaic disease
Symptoms
 Leaves show typical mosaic mottling symptoms. Yellow patches intermingle with
green colour of leaf. The green portions exhibit puckering symptom.
 In severe cases, leaves become smaller and cluster near tip because of shortened
internodes and stimulation of auxillary buds.
 The plants are generally stunted and do not produce pod (Cause Sterility)
Management
 Spray dicofol 18.5 EC 1.0 L or wettable sulphur 40 WP 3.0 kg
 Avoid synthetic pyrethroids as they cause resurgence after repeated spray.

11. Whitefly: Bemisia tabaci (Aleyrodidae:
Hemiptera)
Yellow mosaic of Blackgram, Greengram, Cowpea
and Soybean, Leaf curl in cotton and tobacco
In Blackgram, Greengram, Cowpea and Soybean
1) Initially small yellow patches or spots appear on green lamina of young leaves.
Soon it develops into a characteristics bright yellow mosaic or golden yellow
mosaic symptom.
2) Yellow discoloration slowly increases and leaves turn completely yellow.
In cotton
1) Nymphs and adults suck the sap from the under surface of leaves.
2) The leaves of curled plants are twisted, puckered and thickened with
abnormally prominent veins
3) Severe infestation results in premature defoliation, development of sooty
mould, shedding of buds and bolls and poor boll
In tobacco
1) The leaves of curled plants are twisted, puckered and thickened with
abnormally prominent veins. The plants show stunted growth and the yields are
reduced

12. Whitefly: Bemisia tabaci (Aleyrodidae:
Hemiptera)
Yellow vein Mosaic of Bhendi &Topioca Mosaic
Symptoms
 Clearing of small veins, Yellow area extend into the interveinal portions
 Leaf become chlorotic, Veins thickened,Plants stunted
 Few small malformed fruits.
Management
Resistant Varieties like Arka Anamika, Arka Abhay, Parbhani Kranti
Border cropping – pearl millet / sorghum/ maize
Symptoms
 Infected leaves exhibit chlorotic areas and distortion in leaflets.
 Leaves are reduced in size, misshapen and twisted with bright yellow
areas separated by normal green tissue.
 Tubers show longitudinal splitting.
Management
 Use of resistant varieties like Co 2
 Propagation trough Meristem tip culture, produces virus free plants

13. Whitefly: Bemisia tabaci (Aleyrodidae: Hemiptera) Chilli Leaf curl, Tobacco leaf curl virus (TLCV)
Symptoms
 Lower and upper curling of leaves accompanied by
puckering and blistering of interveinal areas and
thickening and swelling of veins are the main
symptoms.
 Internodes are shortened and plants are stunted.
 Fruiting is stopped and if formed they are small and
deformed

14.  Use the available plant-resistant species and extract seeds only from virus-free plants.
 Raise at least two rows of a barrier crop such as maize, sorghum or pearl millet
around your fields.
 Control whitefly population and protect particularly seedlings from them by
establishing nylon nets over the nursery plants.
 Monitor regularly to detect early infections by looking for symptoms of curled
leaves and stunted growth.
 Position a number of sticky yellow traps or sheets in your field that attracts
whiteflies.
 Ensure a weed-free field and surroundings.
 Collect and destroy early infested plants by burning them.
 Plough deep and burn all plant debris after harvest.
 Encourage beneficial insects by growing mixed cropping.
 Avoid synthetic pyrethroids as they cause resurgence after repeated spray.
Preventive Measures for whiteflies

15. Thrips: Scirtothrips dorsalis, Frankliniella
schultzei (Thripidae: Thysanoptera)
Groundnut bud necrosis virus (GBNV- Tospo virus)
(or) Peanut spotted wilt (or) groundnut ring mosaic
Symptoms
1) Ring spot, mottling and rugosity of leaves.
2) Leaflets size reduced and distorted Necrotic spots on stem and leaf.
3) Bud necrosis Pods wrinkled with black lesions on testa
Management
 Adopt plant spacing of 15x15 cm.
 Spray the crop with 10 per cent AVP at 500 lit/ha, ten and twenty days
after sowing.- AVP (Anti Viral Principle) extracted from sorghum or
coconut leaves

16. Thrips: Frankliniella schultzei, Scirtothrips
dorsalis (Thripidae: Thysanoptera)
Spotted / Bronzy wilt –Tomato spotted wilt virus
(TSWV)
Symptoms
 Thickening of veins, with concentric rings
 Bronzing of leaves
 On fruits, Pale red or yellow areas with circular marking
 Shape affected with no seeds
 Lycopene content is reduced
Management
 Avoid transplanting young plants during wet &
warm month
 Aluminium surfaced plastic mulch

17. Brown leafhopper: Cestius phycitis, Hishimonas
phycitis (Cicadellidae, Hemiptera)
Vector for Little leaf - Phytoplasma
Symptoms
 Reduction in size of leaves, petiole
 Leaves become sessile, thin, soft and pale green
 Growth of axillary buds stimulated
 Shortening of internodes – gives bushy appearance
 Floral parts modified into green structures
 No fruits formed – plants sterile
 If fruits formed, mummified and cling on plants,
Management
 Res. Var. like Arka sheel, Pusa Purple Cluster
 Tolerant var. Black Beauty, Brinjal Round, Surati
 Avoid Susceptible – Pusa Purple Long

18. Green peach aphid: Myzus persicae (Aphididae:
Hemiptera)
Mosaic of crucifers, cucumbers, tomato, potato
& Yellow dwarf of onion, Potato leaf roll virus
Symptoms
In of crucifers, cucumbers
 Leaves show clear mosaic symptoms.
 Affected leaves are puckered and deformed.
 Internodes are shortened.
 Leaves attain only half the size of normal leaves.
 Flowers are dwarfed and few in number. Fruits are small with
yellowish green mottling
 Incase of Cauliflower and cabbage production of small and poor
quality curds &heads
In Potato
 Tip and margins of leaves roll upwards
 Midrib takes the shape of spoon and later into funnel
 Leaflets brittle ,become yellow and then brown

19. Banana aphid: Pentalonia nigronervosa
(Aphididae: Hemiptera)
Bunchy Top/Curly Top /Cabbage Top/Strangle
Disease - Banana Bunchy Top Virus (BBTV)
Symptoms
 Green streaks range from a series of dark green dots to a continuous dark
greenline (Morse code)
 In badly attacked plants, leaves are small, erect and bunched together at the apex or
crowded at the top (Bunchy top)
 The petiole, mid rib and lamina become more brittle and can easily be snapped
when bent or crushed
 Plants show marked stunting .
Management
 Propagation trough Meristem tip culture, produces virus free plants
 Scymnus craccivora , Chilomenes sexmaculatus, Chrysoperla carnea.
 Use entomopathogens, Beauveria bassiana

20. Cardamom aphid: Pentalonia nigronervosa f.
caladii (Aphididae: Hemiptera)
Vector of the mosaic or 'Katte' virus of
cardamom
Symptoms
 Spindle shaped chlorotic flecks appear on the youngest leaves in an
infected clump; these flecks progress into light green, discontinuous stripes
which run parallel to the vein.
 Mosaic symptoms are also frequently mixed. As the virus is systemic, the
disease spreads throughout the clump
 After an year reduction in leaf size and stature of the plant is visible.
 The affected clumps produce slender tillers and shorter panicles.
Management
1. Removal of Colocasia and other hosts in the vicinity of cardamom
plantation is recommended.

21. Aphid: Toxoptera citricidus, T. aurantii
(Aphididae: Hemiptera)
Tristeza / Quick decline / Stem pitting disease -
Citrus Tristeza Virus
Symptoms
• Leaves of acid lime exhibit large number of vein flecks (elongated
translucent areas).
• Die-back symptom is commonly associated.
• Characteristic pits or depressions on wood (stem pitting) can be
clearly seen on the stem after removal of bark.
Management
 Release of coccinellid predator, Menochilus sexmaculatus @ 50 per tree
 Lime is highly susceptible

22. Shoot psyllid: Diaphorina citri (Psyllidae:
Hemiptera)
Vector For Citrus Greening, Fastidious
Vascular Bacteria (Phloem Inhabiting Bacteria)
Symptoms
 Leaves may be completely yellow or yellow with green veins and
small green dots
 Fruits are small, with aborted seeds and drop prematurely.
Management
 Spray tetracycline 500 ppm to inhibit multiplication of pathogen.
 Prune the affected trees and dried shoots.
 Conserve natural enemies like parasitois Tetrastichus radiates and predators
like Coccinella septumpunctata, C.rependa, Chilomenes sexmaculata, Chilocorus
nigritus, Brumus suturalis, Chrysoperla carnea.
 Spray any of the insecticides viz., NSKE 5 %, neem oil 10 L, dimethoate 30 EC
3.0 L

23. S.No Vector Disease & Causal agent Cro
1 Green leaf hopper
Nephotetix virescence
Rice Tungro Virus, Rice Yellow Dwarf And
Transitory Yellowing Diseases
Rice
2 Brown plant hopper
Nilaparvata lugens
Vector of Grassy Stunt, Ragged Stunt And Wilted
Stunt Diseases
Rice
3 Bean aphid
Aphis craccivora
Groundnut rosette assistor virus (GRAV) Groundnut
4 Leaf hopper
Orosius albicinctus
Phyllody – Phytoplasma Gingelly
5 Red gram sterility mite
Aceria cajani (NON-
INSECT)
Pigeon Pea Sterility Mosaic Disease Redgram
6 Whitefly: Bemisia tabaci Yellow Mosaic Virus Blackgram,
Greengram, Cowpea
and Soybean
Leaf curl Virus Cotton , Chilli and
Tobacco
Yellow Vein Mosaic Virus Bhendi &Topioca

24. 7 Thrips
Scirtothrips dorsalis,
Frankliniella schultzei
Groundnut Bud Necrosis Virus (GBNV- Tospo virus)
(or) Peanut Spotted Wilt (or) Groundnut Ring Mosaic
Groundnut
Frankliniella schultzei,
Scirtothrips dorsalis
Spotted / Bronzy wilt –Tomato spotted wilt virus
(TSWV)
Tomato
8 Brown leafhopper
Cestius phycitis
Little leaf - Phytoplasma brinjal
9 Green peach aphid:
Myzus persicae
Mosaic Virus Crucifers, Cucumbers,
Tomato, Potato
10 Banana aphid
Pentalonia nigronervosa
Bunchy Top/Curly Top /Cabbage Top/Strangle Disease
- Banana Bunchy Top Virus (BBTV)
Banana
Pentalonia nigronervosa
f. caladii
'Katte' virus disease Cardamom
11 Aphid
Toxoptera citricidus, T.
aurantii
Tristeza / Quick decline / Stem pitting disease - Citrus
Tristeza Virus
Citrus
12 Shoot psyllid
Diaphorina citri
Citrus Greening, Fastidious Vascular Bacteria (Phloem
Inhabiting Bacteria)
Citrus

25. IPM for Vector Control
• Control measures are not known for majority of viral diseases.
• Hence, mechanical, cultural methods are mostly recommended.
• The infected plants should be uprooted and burnt or buried to avoid further infection.
• Avoid monoculturing of a crop.
• Use seeds from healthy plants of previous season
• Growing nursery in protected structures
• Removal of infected seedlings and weed hosts from nursery as soon as seen
• Treatment of seedlings with proper systemic fungicides to control vector

26. Cont,
• Use of yellow sticky traps just above the plants to control insect vectors
• Use light traps to check the some of homopteran insects.
• Destroying previous year susceptible crops, particularly solanaceous weeds and
volunteer plants
• Good weed control in the crop that may be alternative host to virus and vectors
• Transplanting dates should be adjusted to avoid peak season of the vector population
• Use of reflective (silver colour) plastic mulch
• Use of live mulches, border crops or hedges which are more attractive to the vectors
than main crop

27. References
• Arjunan.G. Karthikeyan, G, Dinakaran ,D. Raguchander,T. 1999 Diseases of Horticultural Crops, AE
Publications, Coimbatore.
• Muthukrishnan,N., N.Ganapathy, R.Nalini and R.Rajendran.2005. Pest Management in Horticultural
Crops. New Madura Publishers, Madurai. 325p. {ISBN: 81-902832-0-0}
• David, B.V. and V.V. Ramamurthy. 2011. Elements of Economic Entomology, Namrutha Publications,
Chennai. 386 p. {ISBN: 978-81-921477-0-3}