SCI 355B: Lecture 13 Insects and Diseases I: Plants, Livestock, Pets, and Humans

Plant Feeding Insects • Phytophagous insects are generally considered to feed on green plants. • They attack roots, stems, leaves, flowers, and fruits, either as larvae or as adults or in both stages. • The most serious plant pests are Hemiptera, Homoptera, Orthoptera, and Lepidoptera. • Hemiptera and Homoptera feed “internally” on plant “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 by the reaction of plants to chemicals produced by 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 to human populations. However, the term is widely used in studies of animal & plant populations. • Vector - an organism which spreads disease from one host to another. Arthropods spread bacterial, viral, fungal and protozoan pathogens by two main mechanisms. Either via their bite, or via their feces or direct contact.

Effects of Plant Feeding: Pathogen Transmission • Insects and mites cause several hundred different and serious plant diseases directly through feeding or transport and inoculate plants with pathogens such as: – – – –

bacteria viruses fungi nematodes

Insects & Plant Pathogens • Insects are the most important vectors of plant viruses • Plant diseases spread by insects can be crucially important to the profitable production of some crops. • Billions of dollars at stake

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Insects & Plant Viruses • Aphids are the most important vectors of plant viruses • Although Insects normally acquire viruses by feeding on already infected plants, some plant viruses can invade the developing eggs or embryos within a 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 the virus to the aphid vector’s mouthparts. • Once inside the insect, some viruses utilize bacteria (already present in the insect) to gain entry into the salivary glands.

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 diseases do not require insects as vectors, relying instead on rain, wind,soil, seed dispersal, or other means of transport and entry to plants. • However, insect vectors do contribute to the spread of some bacterial pathogens of plants.

Insects & Bacteria

• Example: Fire blight, an important bacterial disease of pome fruits, such as pears and apples. • Insects have an important role in spreading the bacterium (Erwinia amylovora)among blossoms while foraging. • “burnt” appearance of affected blossoms and twigs. Flowers turn brown and wilt, discolored oozing patches, form on branches.

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Incidental bacterial transmission • Stewart’s wilt of corn -transmission of the bacterium (Erwinia stewartii) by corn wilt beetle. • Cucurbit wilt (cucumber, melons, squash)beetle transmission of the bacterium (Erwinia tracheiphila) – bacteria enter feeding wounds made by the beetle vectors, but not much is known of how the beetles introduce the bacteria into plants

Insect vector required for bacteria transmission • Some bacterial pathogens require insect vectors for plant-to-plant movement and to enter and infect plants. • e.g.,Pierce’s Disease, Citrus stubborn disease (Spiroplasma citri) and the corn stunt spiroplasma (Spiroplasma kunkelii)

Other examples • aster yellows phytoplasma in lettuce, carrot, celery, and other vegetable crops • X-disease phytoplasma in stone fruits such as peach or cherry. • Lethal yellowing disease of palms has been a major factor in killing coconut palms in Africa and the Caribbean. • pear decline disease

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Insects & Fungi • The fungi are probably the most diverse and important plant pathogens, but most do not require mobile vectors such as insects. • However, some fungi are specialized for transmission by insect vectors.

Insects & Fungi • Dutch elm disease, the best known example of a fungal disease of plants transmitted by an insect vector. • The causal fungus, Ophiostoma ulmi, grows into a spore under the bark and into the woody tissues of elms. • Adult bark beetles, are attracted to distressed elms. • disease fungus grows in beetle brood chambers and produces sticky spores that attach to the body and mouthparts of the adult beetles

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Fiscal Year 2009 - Budget  $95 Billion  Nutrition 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 Plant Diseases in California • Various plant feeding Hemiptera and Homoptera (both with piercing-sucking mouthparts) are the major insect vectors of plant diseases. Causative agents= bacteria and 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 Four Commodities 1.Milk and Cream = $5.22 billion 2. Grapes = $3.2 billion 3. Nursery = $2.4 billion 4. Almonds = $2.3 billion California agriculture is a $31.7 billion industry that generates $100 billion in related economic activity

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Of the top 10 agricultural producing counties nationwide, nine are located in California. Fresno County is the #1 county in the nation with $4.64 billion in agricultural value. Fresno County’s agricultural productivity outpaces 24 of the 50 states.

Homalodisca vitripennis

GWSS host plants Abelia, 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, Cape chestnut, 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, Fishtail palm, 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, Mock orange, 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, Trumpet creeper, 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, Yellow jessamine, 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

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