Great Plains Growers Conference And Trade Show St. Joseph, MO January 12, 2018 Management Of Insect And Mite Vectors Of Vegetable Diseases Raymond A. Cloyd Professor and Extension Specialist in Horticultural Entomology/Plant Protection Kansas State University, Manhattan, KS Phone: 785-532-4750 Email: rcloyd@ksu.edu
Overview: What To Expect Introduction Vector: characteristics Insect-pathogen relationships Arthropod (insect and mite) vectors Vector management Questions and discussion
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 Ways 1. 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 Vectors 1. 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!