Hemiptera: Plant Insect Interactions

Hemiptera

Order composed of true bugs, largest order of hemimetabolous insects

Feeding Ecology

• Most are plant feeding but some are hematophagous and predatory

• Significant pests due to feeding:

• Bedbugs

• Kissing bugs

• Aphids, whiteflies

• Psyllids

• Scales

Plant-Insect Interactions

• Plants are important sources of food and shelter for insects

• Half of all insect species are phytophagous (feeding on plants)

Insect Feeding

• Insect feeding behaviors are primary way insects' impact human society

• Pests and diseases cause up to 40% crop yield losses each year worldwide

• Two types of injury: direct injury and indirect injury

Direct Damage: Plant Feeding

• Feeding on plant tissues reduced leaf surface available for photosynthesis, disrupts plant growth

• Tunneling through plants also distorts growth

Insect Mouthparts

• The mandibulate (chewing) is basic type from which others are derived

Piercing-Sucking Mouthparts: Hemiptera

• Characteristic of Hemiptera is piercing sucking mouthparts

• Majority feed on plant fluids: xylem and phloem

• Cause direct damage by weakening plant

Hemiptera Feeding

• Phloem sap, has high in sugar and nitrogen, low in amino acids

• Large quantities of phloem needed to meet nutritional requirements

• No digestion required (except for hydrolysis of sucrose)

Phloem Feeding Insects

• Phloem feeding Hemiptera typically have gut symbiotic micro-organisms to convert amino acids from sugar

• Aphids house Buchnera which is transferred vertically

• Symbionts recycle glutamate into essential amino acids

Xylem Feeding

• Occasionally feed on Xylem sap

• More dilute: even lower in amino acids

• Feed on xylem when facing dehydration periods to replenish water balance

Phloem Feeding

• Adaptation to dilute diet is filter chamber

• Part of the gut looped back on itself as countercurrent exchanger

• Permits nutrients to be separated from excess water

• Residue mostly water with sugars and amino acids, excreted as honeydew

The Filter Chamber

• Well- developed filter chambers characteristic of insects that feed on xylem and phloem

Honeydew

• Is a rich sugar solution that is the excretory product of phloem feeding Hemiptera

• Utilized by other insects as a carbohydrate food source

• Basis of the ant-aphid mutualism

Ant-Aphid Mutalism

• Aphids and aphids form a symbiotic relationship where bothspecies benefit

• Ants gather and eat the honeydew secreted and in return protect aphids from predators

Indirect Damage

• Hemiptera can damage plant with factors that are secondary to feeding

• Transmission of diseases, fungus to a crop

• May also cause damage to crop aesthetics and reduce marketability

Pest Damage

• Cause immediate injury or disturbance

• Cosmetic damage: injury to aesthetic value

• Damage that detracts from appearance of ornamental plants

• Thrips that feed on rinds of oranges create scars but do not change nutritional value

Indirect Pests

• Honeydew excreted from insects causes injury by facilitating growth of sooty mold

• Sooty mold can significantly reduce photosynthesis on leaves

• Direct injury if it falls on cotton fibers

Vectors of Disease

• Indirectly, insect can vector disease carried in the saliva

• Vector refers to organism that carries pathogen

• Many plant disease are transmitted by Hemiptera and host plants dictate the transmission efficacy

Hemiptera: Psyllids

• Phloem feeders: tend to be very host-specific

• Citrus greening disease associated with bacteria coevolved with vector: Asian citrus psyllid

• Major disease which can reduce citrus quality, flavor, and production, death of trees

• Found in Florida in 1998, and has since spread across the southern US

Hemiptera: Piercing SuckingMouthparts

• Some Hemiptera are predators of other arthropods

• Saliva often contains digestive enzymes to liquefy internal organism

• Many aquatic species are exclusively predatory

Hemiptera: Parasitic

• All triatomine bugs are potential vectors, most significant are those adapted to live among humans

• Vectors of Chagas Disease, caused by Trypanosoma cruzi

• Endemic to Latin America, but present in U.S. and Spain

Hemiptera: Kissing Bugs

• Spread by feeding then defecating near wound

• If infected feces are introduced to the wound (by scratching etc.) infection can occur

• Acute stage of infection lasts a few weeks or months and may have mild symptoms

• Fever

• Aches

• Loss of appetite

Hemiptera: Bed Bugs

• Cimex sp. are obligate ectoparasites which feed on blood of birds and mammals

• Small, flattened bodies allows them to hide easily in bedding

• Robust, resistant to temperature changes and many pesticides

• While bed bugs do not vector disease, are an extreme nuisance and can spread easily