Post on 14-Aug-2020
Great Plains Growers Conference And Trade
Show
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!