Insect Vectors of Plant Diseases

Insect vectors of plant diseases: A vector is capable of transmitting various pathogens from one host to another. All insect Vectors acquire the disease causing organisms feeding on the diseased plants and transmit them to healthy plants. Insects having piercing or sucking type of mouthparts, biting or chewing type of mouthparts transmit the diseases.

Post	Insect Vectors of Plant Diseases
Main subject	Entomology

Also read: Insect-pests of Winter Crops Multiple Choice Questions

Why are homopteran insects efficient vectors?

Homopteran insects are very efficient vectors due to the following features:

Making frequent probes into host plants.
Production of winged migratory individuals.
Deposition of progenies on each of the many plants.
They don’t cause the wholesome destruction of cells during feeding.

List of contents
(01). List of insect vectors of plant diseases
(02). Management practices
(03). Multiple Choice Objective Questions
(04). Answer key

(01). List of insect vectors of plant diseases

Viruses.
Phytoplasma.
Bacteria.

1.1: Viruses

Virus can live and multiply only in living cells.
Mosaic, leaf curl, etc., are examples of diseases caused by virus.
About half of the insect vectors are aphids, a third are the leafhoppers.

Types of viruses

Non-persistent viruses.
Semi-persistent viruses.
Persistent viruses.

Non-persistent viruses: The efficiency of transmission of non-persistent virus is mainly affected by modifying the time of feeding and by starving the vectors before and after feeding. Example: Aphids.

Semi-persistent viruses: Semi-persistent viruses are carried in the anterior regions of the gut of a vector. Example: Leafhoppers.

Persistent viruses: These viruses pass through the midgut wall to the salivary glands from where they can infect new host. The incubation or latent period is 10-20 days, and the vectors need not feed on the virus source again and again to retain its ineffective capacity. Such viruses are also known as circulative virus. Transmission is non-mechanical.

Machanism of transmission

Number of forward and backward movements of the inner pair of stylets.
During the forward movements, the fluid flows into them.
During the backward movements, saliva injected.
General, an insect injects by feeding on any part.
Some insects have to inject in phloem.

Virus-vector relationship

Virus-vector relationship is very specific. For example, leaf curl is transmitted by whiteflies. A vector can also acquire and transmit more than one virus to the respective host. For example, the aphid, Pentalonia nigronervosa Coquerel transmits banana bunchy top and cardamom mosaic. More than 60 insects are responsible for transmitting onion yellow dwarf. The most important thing is activity of insect rather than their numbers.

Also read: Major Insect-pests of Rice

List of some important vectors of plant viruses

Vector(s)	Virus(es)	Host(s)
Aphis craccivora Koch	Papaya mosaic and others	Papaya and other
Nilaparvata lugens (Stal)	Grassy stunt	Rice
Brevicoryne brassicaceae	Cauliflower mosaic	Cabbage, cauliflower

1.2: Phytoplasma

Phytoplasma are important insect-transmitted agents.
They cause more than 700 diseases in plants.
The most successful order of insect phytoplasma is the Hemiptera.

Machanism of transmission

Phytoplasma are phloem limited.
Only phloem feeding insects can potentially acquire and transmit the pathogen.
Phloem feeding insects aquire phytoplasma passively during feeding in the plant.
During the latent period, phytoplasma move through and replicate in the vector’s body.
To be transmitted to plants, phytoplasmas must penetrate specific cells of the salivary glands and high levels must accumulate in posterior acinar cells of the salivary gland before they can be transmitted.

Vector-phytoplasma relationship

The interaction between insects and phytoplasmas is complex and variable.
A complex sequence of event is necessary for an insect to aquire and subsequently transmit phytoplasmas to plants.
Polyphagous vectors have the potential to inoculate a wider range of plant species, depending on the resistance to infection of each host plant.

List of some important vectors of phytoplasma

Vector(s)	Mycoplasma(s)	Host(s)
Cestius phycitis	Brinjal little leaf	Brinjal
Euscelis lineolatus	Clover phyllody	Most clovers
Scaphytopius acutus	Aster yellow	Aster, carrot, barley, celery

1.3: Bacteria

Categories of bacterial diseases:

Wilting: Due to invasion of the vascular system.
Necrotic blights, rots and leaf spots.
Over growth, e g., crown gall.

Machanism of transmission

Pathogenic bacteria apparently cannot enter plants directly through unbroken cuticle but get in through insect or other wounds.
The fact that the plant pathogenic bacteria are unable to penetrate plant tissue without a court of entry has led to realisation of significance of the role of insects in transmission.
Insects contributes through feeding and oviposition wounds, as a mechanical carrier of the organism on its body and in some cases, by virtue of a mutualistic relationship between the organism and the insect.

List of some major vectors of bacterial diseases of crop plants

Vector(s)	Disease(s)	Host(s)
Bees, wasps, flies, ants and aphids	Fire blight	Apple, pear, quince
Diaphorina citri	Citrus canker	Citrus
Hylemya cilicrura	Potato blackleg	Potato

1.4: Fungi

More than 8,000 species are known to cause plant diseases.
Mechanical transmission is common.
Examples: Aphids, leafhoppers, mealy bugs, whiteflies, etc.

List of some principal vectors of fungal diseases of crop plants

Vector(s)	Disease(s)	Host(s)
Melanoplus differentialis	Cotton wilt	Cotton
Several species of insects visiting flowers	Ergot of bajra	Bajra
Scolytus multistriatus	Dutch elm disease	Elm

(02). Management practices

Use of healthy seeds.
Cultural control.
Resistant varieties.
Biopesticides.
Chemical controls.

Use of healthy seeds: Use of certified seeds. Heat treatment of seeds. Test the seeds by indexing.

Cultural control: Intercropping, for example, the incidence of yellow vein mosaic of okra is reduced by intercropping with soybean. Plant spacing such as close spacing reduces the incidence of French bean crinkle stunt disease. Removal of weeds and alternate hosts of viruses and vectors helps to reduce the incidence of diseases.

Resistant varieties: Resistant varieties are available against virus-borne diseases in many crop plants.

Biopesticides and chemical control: Control of insects by using parasitoids, predators, microbials and plant extracts is an eco-friendly approach. Use noval insecticides to control the harmful insects.

(03). MCQ on Insect Vectors of Plant Diseases: Multiple Choice Objective Questions

Also read: Entomology Multiple Choice Questions and Answers

Question 01. How can a vector transmit disease among the plant?

(a). Acquiring the disease causing organism by feeding on plants.
(b). Acquiring the disease causing organism by contact with plants.
(c). Both a and b.
(d). None of the above.

Question 02. Insects from the following order are responsible for the maximum plant disease transmission?

(a). Hemiptera.
(b). Thysanoptera.
(c). Coleoptera.
(d). Orthoptera.

Question 03. Why is a homopteran an effective vector?

Explanation: Because it doesn’t’ cause the wholesome destruction of cells during feeding.

Choose right answer:

(a). Viruses require living cells for their subsistence and multiplication.
(b). Viruses require dead cells for their subsistence and multiplication.
(c). Either a or b.
(d). All of the above.

Question 04. Of which virus is Acryrthosiphon pisum a vector?

(a). Pea mosaic.
(b). Soybean mosaic.
(c). Bean mosaic.
(d). All of the above.

Question 05. Which is not a host plant of Schizaphis graminum?

(a). Maize.
(b). Sorghum.
(c). Turnip.
(d). Sugarcane.

MCQ

Question 06. Which one is responsible for transmitting Hoja blanca in rice plant?

(a). Sogatodes orizicolus.
(b). Nephotettix virescens.
(c). Stenchaetothrips biformis.
(d). Brevennia rehi.

Question 07. Consider about brinjal little leaf?

It is caused by mycoplasma.
Causing agent belongs to orthoptera.
It is one of the rare disease of brinjal.

(a). Only 1 is true.
(b). Only 2 is true.
(c). 1 and 2 are true.
(d). All are true.

Question 08. Which is not a vector of any bacterial disease?

(a). Flea beetle.
(b). Seedcorn maggot.
(c). Slug.
(d). All are known for transmitting bacterial diseases.

Question 09. Which one of the following disease is transmitted by more than 40 pests especially flies, beetle and aphids?

(a). Dutch elm disease.
(b). Cotton wilt.
(c). Ergot of cereals.
(d). Ergot of bajra.

Question 10. Which is an ideal intercrop to reduce the incidence of tomato leaf curl disease?

(a). Okra.
(b). Chili.
(c). Coriander.
(d). Brinjal.

(04). Answer key

1.	c	6.	a
2.	a	7.	a
3.	a	8.	d
4.	d	9.	c
5.	c	10.	c

Insect Vectors of Plant Diseases