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SCI 355B: Lecture 13

Insects and Diseases I: Plants,Livestock, Pets, and Humans

Plant Feeding Insects

• Phytophagous insects are generallyconsidered to feed on green plants.

• They attack roots, stems, leaves, flowers, andfruits, either as larvae or as adults or in bothstages.

• The most serious plant pests are Hemiptera,Homoptera, Orthoptera, and Lepidoptera.

• Hemiptera and Homoptera feed “internally” onplant “juices”.

Effects of Plant Feeding• The feeding of insects can cause:

– yellowing (chlorosis)– silvering– bronzing– necrosis of foliage– wilting– malformation– death

• Phytotoxemia -plant symptoms of caused bythe reaction of plants to chemicals producedby insect feeding (usually in the saliva).

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Vector• Epidemiology - "the study of what is upon

the people", suggesting that it applies only tohuman populations. However, the term iswidely used in studies of animal & plantpopulations.

• Vector - an organism which spreads diseasefrom one host to another. Arthropods spreadbacterial, viral, fungal and protozoanpathogens by two main mechanisms. Eithervia their bite, or via their feces or directcontact.

Effects of Plant Feeding:Pathogen Transmission

• Insects and mites cause several hundreddifferent and serious plant diseases directlythrough feeding or transport and inoculateplants with pathogens such as:– bacteria– viruses– fungi– nematodes

Insects & Plant Pathogens

• Insects are the most important vectorsof plant viruses

• Plant diseases spread by insects canbe crucially important to the profitableproduction of some crops.

• Billions of dollars at stake

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Insects & Plant Viruses

• Aphids are the most important vectorsof plant viruses

• Although Insects normally acquireviruses by feeding on already infectedplants, some plant viruses can invadethe developing eggs or embryos withina female vector insect.

Insects Becoming Infected

• Many viruses produce a small “helper”protein that is thought to act as a“bridge” to aid the attachment of thevirus to the aphid vector’s mouthparts.

• Once inside the insect, some virusesutilize bacteria (already present in theinsect) to gain entry into the salivaryglands.

Insects & Plant Viruses

• potato virus Y (aphid)• potato leaf roll virus (aphid)• Lettuce necrotic yellows virus (aphid)• rice tungro disease (leafhopper)• maize chlorotic dwarf virus (leafhopper)• rice dwarf virus (leafhopper)• Tomato spotted virus (thrips)

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Insects & Bacteria

• Unlike viruses, most bacterial diseasesdo not require insects as vectors,relying instead on rain, wind,soil, seeddispersal, or other means of transportand entry to plants.

• However, insect vectors do contribute tothe spread of some bacterial pathogensof plants.

Insects & Bacteria

• Example: Fire blight, an important bacterialdisease of pome fruits, such as pears andapples.

• Insects have an important role in spreadingthe bacterium (Erwinia amylovora)amongblossoms while foraging.

• “burnt” appearance of affected blossoms andtwigs. Flowers turn brown and wilt,discolored oozing patches, form on branches.

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Incidental bacterialtransmission

• Stewart’s wilt of corn -transmission of thebacterium (Erwinia stewartii) by corn wiltbeetle.

• Cucurbit wilt (cucumber, melons, squash)-beetle transmission of the bacterium (Erwiniatracheiphila)– bacteria enter feeding wounds made by the beetle

vectors, but not much is known of how the beetlesintroduce the bacteria into plants

Insect vector required forbacteria transmission

• Some bacterial pathogens requireinsect vectors for plant-to-plantmovement and to enter and infectplants.

• e.g.,Pierce’s Disease, Citrus stubborndisease (Spiroplasma citri) and the cornstunt spiroplasma (Spiroplasmakunkelii)

Other examples

• aster yellows phytoplasma in lettuce, carrot,celery, and other vegetable crops

• X-disease phytoplasma in stone fruits such aspeach or cherry.

• Lethal yellowing disease of palms has been amajor factor in killing coconut palms in Africaand the Caribbean.

• pear decline disease

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Insects & Fungi

• The fungi are probably the most diverseand important plant pathogens, butmost do not require mobile vectors suchas insects.

• However, some fungi are specialized fortransmission by insect vectors.

Insects & Fungi

• Dutch elm disease, the best known exampleof a fungal disease of plants transmitted byan insect vector.

• The causal fungus, Ophiostoma ulmi, growsinto a spore under the bark and into thewoody tissues of elms.

• Adult bark beetles, are attracted to distressedelms.

• disease fungus grows in beetle broodchambers and produces sticky spores thatattach to the body and mouthparts of theadult beetles

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Fiscal Year 2009 - Budget

$95 BillionNutrition Assistance = 63%Farm and Commodity Programs =

15%Conservation and Forestry = 11%Research, Inspection and

Administration = 6%Rural Development = 3% International = 2%

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Major “recent” Insect PlantDiseases in California

• Various plant feeding Hemiptera andHomoptera (both with piercing-suckingmouthparts) are the major insect vectors ofplant diseases. Causative agents= bacteriaand viruses.– PD (Pierce’s Disease)*– HLB (Huanglongbing)-citrus greening– CVC (citrus variegated chlorosis)*– CTV (severe stem-pitting citrus tristeza)*

– *all can be transmitted by sharpshooters

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Insect Transmitted Diseases• Disease:Citrus greening, also known as

huanglongbing.• Insect Vector: Asian Citrus Psyllid,

Diaphorina citri• Causative Agent: phloem-inhabiting

bacterium Candidatus asiaticus• Symptoms: reduces production, destroys the

economic value of fruit, and can kill trees.

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Insect Transmitted Diseases

• Disease: Pierces’ Disease• Insect Vector: Glassy-winged

sharpshooter, Homalodisca vitripennis• Causative Agent: Xyllela fastidiosa, a

bacterium• Symptoms: chlorosis, death

California’s Top FourCommodities

1.Milk and Cream = $5.22 billion2. Grapes = $3.2 billion3. Nursery = $2.4 billion4. Almonds = $2.3 billion

California agriculture is a $31.7 billion industrythat generates $100 billion in related economic

activity

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Of the top 10 agriculturalproducing counties nationwide,nine are located in California.

Fresno County is the #1county in the nation with $4.64billion in agricultural value.

Fresno County’s agriculturalproductivity outpaces 24 of the50 states.

Homalodisca vitripennisHomalodisca vitripennis

GWSS host plantsAbelia, Acacia, Agapanthus, Albizzia, Alder, Aleurites, Amaranth, Ananas, Annona (cherimoya), Apple, Aptenia,Aralia ivy, Arborvitae, Arecastrum, Arizona rosewood, Ash, Asparagus, Aspidistra, Avocado, Azalea, Baccharis,Barberry, Basket plant, Bauhinia, Beard-tongue, Bignonia, Birch, Bird of paradise, Blackberry, Boneset, Bottle tree,Bottlebrush, Bougainvillea, Boxwood, Brunfelsia, Buckthorn, Bugleweed, Cactus, Calla lily, Camellia, Canna, Capechestnut, Carob, Castanospermum, Catawba, Ceratostigma, Champak, Chinaberry, Chinquapin, Chitalpa,Chokecherry, Christmas cactus, Chrysanthemum, Cinnamomum, Citrus, Clytostoma, Cocculus, Cocklebur Cocos,Coffee, Coneflower, Coprosma, Coral tree, Cotoneaster, Cotton, Cottonwood, Crape myrtle, Crassula, Cupaniopsis,Cycad, Date palm, Daylily, Dianthus, Dietes, Dodonaea, Dogwood, Elaeagnus Elaeocarpus, Elderberry, Elm,Ensete, Eriobotrya, Escallonia, Eucalyptus, Eugenia, Euonymus, Euryops, Evening primrose, Feijoa, Fig, Fishtailpalm, Flax lily, Fleabane, Floss-silk tree, Fringe tree, Frogfruit, Gardenia, Gazania, Geijera, Gingko, Gladiolus,Golden-bells, Golden-rain tree, Goldenrod, Grape ivy, Grape, Green ebony, Grewia spp, Guava, Hardenbergia,Hibiscus, Holly, Hollyhock, Honey myrtle, Honeysuckle, Hymenosporum, Itea, Ivy, Japanese aralia, Jasmine, Jojoba,Kaffir plum, Kumquat, Lambsquarter, Laurel, Leadwort, Lettuce, Lilac, Lippia , Locust, Loropetalum, Lychee,Macadamia, Magnolia, Mallow, Mandevilla, Mango, Manzanita, Maytenus, Metrosideros, Milkweed, Milkwort, Mockorange, Morning Glory, Mountain ash, Mountain mahogany, Mulberry, Myoporum, Myrsine, Myrtle, Nandina, Oak,Oleander, Olive, Orange jessamine, Osmanthus, Osteospermum, Palo verde, Pandorea, Papaya, Passion fruit,Pear, Pelargonium, Pepper, chile, Periwinkle, Persimmon, Philodendron, Phlox, Photinia, Pincushion, Pine,Pistachio, Pittosporum, Podocarpus, Pokeweed, Polygonum, Pomegranate, Portulacaria , Powderpuff, Privet,Protea, Prunus, Pyracantha/Firethorn, Ragweed, Raphiolepis, Redbud, Redroot, Rock rose, Rose, Sapium,Sassafras, Schinus, Seaforthia, Senna, Sentry palm, Serviceberry, Shrub verbena, Snapdragon, Solanum, Sonchus,Sorghum, Speedwell, Spider flower Spiderwort, Spurge, St. Bernard's lily, St. John’s-wort, Staghorn fern, Statice ,Strawberry tree, Sumac, Sunflower, Sweet box, Sweet gum, Sword fern, Sycamore, Syzygium, Tecomaria,Ternstroemia, Texas Ranger, Ti, Tipu Tree, Toyon, Trachelospermum, Transvaal, Tree tobacco, Tristania, Trumpetcreeper, Trumpet tree, Tulbaghia, Tulip tree, Tupelo, Tupidanthus, Umbrella tree, Umbrella wort, Viburnum, Vigna,Violet, Walnut, Washington palm, Wild bergamot, Willow myrtle, Willow, Wisteria, Woodbine, Xylosma, Yellowjessamine, Yucca, Zea…

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Diseases Vectored by Sharpshooters

Xylella fastidiosa Pierce’s Disease Almond Leaf Scorch Oleander Leaf Scorch Alfalfa Dwarf Phony Peach Disease Plum Leaf Scorch Liquidamber Leaf Scorch Olive Leaf Scorch Citrus Variegated Chlorosis

Photo by:Fundecitrus

Grape Industry in California 861,000 acres wine/table/raisin Crop production value of $3.2 billion Associated economic impact in CA

$51.8 billion Associated economic impact in the

USA $125.3 billion and 875,000 jobs