Great Plains Growers Conference And Trade

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St. Joseph, MO

January 12, 2018

Management Of Insect And Mite Vectors Of

Vegetable DiseasesRaymond A. Cloyd

Professor and Extension Specialist in Horticultural

Entomology/Plant Protection

Kansas State University, Manhattan, KS

Phone: 785-532-4750 Email: rcloyd@ksu.edu

• Introduction

•Vector: characteristics

• Insect-pathogen relationships

•Arthropod (insect and mite) vectors

•Vector management

•Questions and discussion

Overview: What To Expect

Arthropod Vectors

Associated With Human

Health

Arthropod Vectors Of Plant Diseases

Insect And Mite Pest Feeding Behaviors• Phloem-Feeders: Aphids, Whiteflies,

Mealybugs, Leafhoppers, and Soft Scales

• Xylem-Feeders: True Bugs, Spittlebugs, and

Leafhoppers

• Chewers: Beetles, Caterpillars, and Sawflies

• Miners: Leafminers

• Chlorophyll-Feeders: Spider Mites

• Mesophyll and Epidermal Fluid-Feeders:

Thrips (Western Flower Thrips)

Vector•An organism such as an insect

or mite (arthropod) pest

capable of transmitting a

pathogen (e.g. fungus,

bacteria, virus, or

phytoplasma) from one host

plant to another.

Many

Insects

Serve As

Vectors

Of

Diseases

Diseases Transmitted/Vectored By Insects

•Fungi

•Bacteria

•Viruses

•Phytoplasmas

Pumpkin Plant Exhibiting Viral Symptoms

Characteristics Of An “Efficient”

Insect Vector• Broad host range: feed on a wide-range of

plants and weeds.

• Highly mobile: can locate new plant hosts and

habitats.

• Structure of mouthparts: insect vectors with

piercing-sucking mouthparts (especially for

viral transmission) have needle-like stylet

bundles with two mandibular and two maxillary

stylets.

Dissemination Of Pathogens By Insect Vectors

•Direct: insect vector directly

introduces the pathogen (e.g.

virus) into the plant during

feeding.

• Indirect: the pathogen is

“released” into the plant as the

insect vector feeds.

Transmission Of Plant Diseases• Direct: associated with the type of feeding

behavior of insects and what occurs during the

feeding process. Insect pests may contain plant

viruses on their stylets or the virus may

accumulate internally.

• Indirect: associated with insect pests either

carrying spores of diseases (e.g. fungi) or creating

wounds that allow entry of diseases (e.g. fungi

and bacteria). Feeding damage may result in

increased plant susceptibility to fungi and/or

bacteria.

Viruses: Occurrence In Insect Vector

And Transmission

1. Persistent (circulative)

Transmission

2. Non-persistent Transmission

3. Propagative (persistent)

Transmission

Viruses: Occurrence In Insect Vector

And Transmission* Persistent (circulative) Transmission: virus particles

accumulate inside the body of the insect vector, and are

introduced into the plant during the feeding process.

Vectors can transmit a virus for several days or weeks;

however, this depends on how long insects feed on

infected plants. The virus does not multiply (replicate) in

insect vector, but has to circulate in order to be

transferred to the plant. The virus enters the salivary

glands via the hemolymph (fluid similar to blood that

circulates inside the body of insects). Replication of the

virus is restricted to phloem tissues in the plant.

Disease Transmission

By Aphid

Viruses: Occurrence In Insect Vector

And Transmission * Non-persistent Transmission: sucking insects

such as aphids carry plant viruses in their

mouthparts or stylets. The virus does not enter

the hemolymph. Insects can transmit a virus

only within a short period of time after

acquisition. The virus attaches to the inside of

the stylet (mouthpart) and foregut, and is

introduced into plants during salivation and

regurgitation.

Aphid

Feeding

In Phloem

Sieve

Tubes

Viruses: Occurrence In Insect Vector

And Transmission

* Propagative (persistent) Transmission: virus must

multiply in the insect vector in order to complete

persistent, propagative transmission to plants.

Transmission of the virus is restricted to phloem

tissues in the plant. In addition, the virus replicates

in plant tissues and in different organs in insect

vectors. Virus particles enter the salivary glands

through the hemolymph or connecting tissues such

as the nervous system or trachea (breathing tubes).

Disease Transmission

By Aphid

Issues Associated With Insect Vector-Pathogen

Interactions

• Insect vector movement is an international issue due

to expanding travel and trade (commerce) of plant

material, resulting in a greater probability of

spreading insect vectors (and subsequently pathogens)

among countries.

• Aggressiveness of new insect vector species are a

concern, particularly exotic species, which appear to

be more aggressive in new habitats. For example,

ambrosia beetles, which are typically considered

secondary insect pests, attack “healthy” trees and

cause plant death.

Insects And Mites That Can Vector Vegetable Diseases

• Aphids

• Whiteflies

• Thrips

• Leafhoppers

• Beetles

• Psyllids

• Spider Mites

Aphids Are Major Vectors Of Many Plant Viruses

Associated With Vegetable Crops

Aphids Are Major Insect

Vectors Of Plant Viruses

Green Peach Aphid (Myzus persicae): Vector

Of Many Plant Viruses

During The

Feeding

Process,

Aphids

Transmit

Viruses

Disease Transmission

By Aphid

Viruses Transmitted By Aphids* Cucumber mosaic virus (CMV; NP)

* Pepper mottle virus (PMV)

* Potato virus Y (PVY; NP)

* Tomato mild mottle virus (TMMV)

* Watermelon mosaic virus (WMV;

NP)

* Lettuce mosaic virus (LMV; NP)

Whiteflies

Whiteflies Vector Many Viruses

* Geminiviruses

* Closteroviruses

* Begomoviruses

* Potyviruses

RNA Viruses Transmitted By Whiteflies

* Cucumber vein yellowing

virus (CYYV)

* Cucurbit yellow stunting

disorder virus (CYSDV)

* Tomato chlorosis virus

(ToCV)

Additional Viruses Transmitted By Whiteflies

* Tomato leaf curl virus (ToLCV; P)

* Tomato yellow leaf curl virus

(ToYLCV; P)

* Lettuce infectious yellows virus

(LIYV)

* Potato yellow vein virus (PYVV)

* Tomato chlorosis virus (ToCV)

Western Flower Thrips Adults: Vector Tomato Spotted Wilt

Virus (TSWV) And Impatiens Necrotic Spot Virus (INSV)

Western Flower Thrips

Life Cycle

* Egg

* Larvae (n=2)

* Pupae (n=2)

* Adult

Life Cycle May Be

Completed In 18 To 24

Days Depending On

Temperature

Thrips Feeding Behavior: Piercing-Sucking

Impatiens Necrotic Spot Virus

Tomato Spotted Wilt Virus Symptoms On Tomato Leaves

Tomato Spotted Wilt Virus Symptoms On Tomato Fruit

Leafhoppers: Certain Species Are

Vectors Of Diseases

Diseases Transmitted By Leafhoppers

* Beet curly top virus (BCTV)

* Aster yellows

(phytoplasma)

* Pierce’s disease, Xylella

fastidiosa (bacteria)

Aster Yellows

On Echinacea

Aster Yellows: Vectored

By The Aster

Leafhopper (And Other

Leafhopper Species)

Striped Cucumber Beetle And Spotted

Cucumber Beetle Adult: Both Vector

Bacterial Wilt Of Cucumber

Bacterial Wilt Of Cucumber: Vectored By Striped

Cucumber Beetle And Spotted Cucumber Beetle

Certain

Flea

Beetle

Adults

Can

Transmit

Diseases

Flea Beetle Transmission Of Fungus

May Occur Four Ways1. Spores (conidia) of fungus are present on

the body of flea beetle adults.

2. Feeding by flea beetle adults provides sites

for spores to enter the plant.

3. Spores of fungus are present in the feces of

adult flea beetles.

4. Mouthparts of flea beetle adults are

contaminated with spores of fungus.

Potato/Tomato Psyllid

(Bactericera cockerelli) and Asian

Citrus Psyllid (Diaphorina citri)

Potato/Tomato

Psyllid Vectors Zebra

Chip Bacterial

Disease (Candidatus

Liberibacter

solanacearum) Of

Potatoes

Leafminer Female Puncture Wounds May Predispose

Plants To Infection By Fungal Pathogens

Twospotted

Spider Mite

(Tetranychus

urticae) Can

Transmit

Diseases

Vector

Management

Weed Management

Importance Of Weed Management• Control weeds in and around crops and

greenhouse areas as weeds host insect pests and the viruses they spread.

• Many broadleaf weeds are susceptible to and serve as a refuge for insect (and mite) pests such as aphids and leafhoppers. Weeds may also serve as over-wintering sites for certain insect and/or mite pests.

• Weeds may harbor certain viruses vectored by insect pests.

Many Weeds Serve As Reservoirs For Insect Pests

That Vector Diseases

Vector Management• Primarily involves “controlling” insect or mite

vector with insecticides or miticides since it is

“easier” and less expensive, in general, to deal with

the insect or mite vector than the pathogen. It is

important to minimize spread of disease to other

plants. Furthermore, mortality must be “high” since

any insect or mite vectors that survive could

continually spread the pathogen.

• Due to association with pathogen, insect or mite

vector thresholds are extremely low (sometimes

zero).

Insecticides And Insect Vectors1. Insecticides are more effective against insect vectors associated with persistent

transmission due to the long feeding probes. However, insecticides are less

effective against insect vectors affiliated with non-persistent transmission

because acquisition and inoculation occur very rapidly (e.g. seconds). Insecticide

may not kill individuals fast enough before acquisition and inoculation.

2. Insecticides must kill a high percentage (>90%) of insect vectors to prevent

spread of viruses from plant to plant between application intervals.

3. Frequent applications are required to protect new plant growth from insect

vectors, and thorough coverage of all plants parts is essential in order to kill as

many insect vectors as possible.

4. For non-persistently transmitted viruses, insecticides must kill insect vectors

rapidly, repel insect vectors, or modify insect vectors behavior to prevent

probing. For instance, pyrethroid insecticides kill insects quickly, repel insects,

and may reduce probing time.

5. However, applying insecticides “too frequently” may lead to resistance

developing in insect vector populations.

When Applying Insecticides Or Miticides It Is Important To

Obtain Thorough Coverage Of Leaf Undersides—Why?

The Life Stages (Eggs, Larvae,

Nymphs, Pupae, And Adults) Of

Insect And Mite Pests Are Typically

Located On Leaf Undersides

Barrier: Row Covers Protect Cucumbers

From Beetle Vectors

Using Reflective Mulch Inside Hoop House To Reduce Incidence Of Aphid

And Thrips Populations; Thus Mitigating Potential For Viral Transmission

Summary* Insect pests with sucking or chewing

mouthparts can directly or indirectly

transmit diseases (e.g. viruses, fungi, and

bacteria) to vegetable crops in greenhouses

and outdoors.

* Weed removal and timely applications of

insecticides (and miticides) may alleviate

problems with insect (and mite) pests

transmitting diseases.

Thank You For Your

Attention!

I Hope You All

Learned Something!