According to some estimate it is evaluate that the total population of insect around the world can imagine by this comparison that the mass of 40 tons of insects is equal to one human.
Conservative estimate suggests that there are 2 million species of insects, but this estimated figure can extend to 30 million because scientist believe that there are more insect species that have not been described then there are those insect species which have been already described.
According to some scientist there are 99% among the total insect population are innocuous and inoffensive but only 1% of these are consider as a pest because this 1% challenge human beings for food, feed and shelter.
Insect as a Carrier
The term carrier is used to describe an individual that is infected by a disease agent and can disseminate that disease agent but shows no sign of clinical disease. So, the carrier has no symptoms of a disease but still passes it on to someone else. Insect play major role as a carrier of pathogen for example House fly (M. Domesticae).
Insect as Vector
A vector is “an insect or any living carrier that transports an infectious agent from an infected individual or its wastes to a susceptible individual or its food or most immediate surroundings” These are main diseases which are transmitted by vector cotton leaf curl virus (White-Fly), Yellow Fever (flea), Dengue (Mosquitos) and many other.
In Crops
In many cases insect severs as a carrier and vector of plant diseases if they are not available then there is no transmission of disease in plants. It is estimated that 30-40% of the losses and damage caused by plant diseases is due to the direct or indirect effects of transmission of plant pathogen. Plant diseases appears in various symptoms, usually spots of various shapes and sizes on leaves, shoots, and fruit; as cankers on stems; as blights, wilts, and necrosis of shoots, branches and entire plants; as, malformations, discolorations, galls, and root rots, etc.
Regardless of their appearance, plant diseases interfere with one or more of the physiological functions of the plant (absorption and translocation of water and nutrients from the soil, photosynthesis, etc.) and thus the productivity and quality reduced ultimately under the stress of microbes. Almost all plant pathogenic viruses, many fungi, bacteria, protozoa also nematodes are transmitted with the assistance of insect generally carried internally which are associated with their internal mechanism.
There are many other pathogens which are being transported externally on their body parts like legs, antennae, mouth parts, etc. On the contrary, the insects that transmit the other pathogens listed below internally are very specialized and specific for the pathogen they transmit and belong to a certain species or genus of insects.
Insect as a Vector and Carrier of Different Plant Diseases
Major order of insect which cause crop losses by transmitting lethal pathogen these are Hemiptera, Thysanoptera, Diptera, Coleoptera and Hymenoptera.
In order hemiptera (True Bugs) members of following families serves as a vector and carrier of following diseases.
- Piesmatidae Ash-gray leaf bugs are vectors of the sugar beet savoy virus, beet rosette disease and beet leafcurl virus.
- Aphidoidae Aphids act as vector over 150 different kinds of plants viruses like tomato spotted wilt, tobacco mosaic, pea wilt, cabbage black ringspot, cucumber virus etc.
- Cicadellidae Leafhopper also transfer 80 types of known plant PATHOGENS these are viruses, spiroplasmas and mycoplasma like organisms (MLOs). Here are some major diseases phony peach, dwarf disease of rice, beet curly top, blueberry stunt etc.
- Fulogoroidae Planthopper it also plays role in transmitting about 20 types of plant diseases like rice stripe, sugarcane Fiji disease, tillering disease, and maize mosaic virus.
- Aleyrodidae Whitefly took part in transferring yellow mosaic disease in almost 20 kinds of plant species comprising cotton leaf curl virus, leaf curl virus in potato, tobacco, tomato, and same as other plant.
- Membracidae Treehoppers members of this family play major role in pathogen transmission of eggplant (Solanaceae)
- Pseudococcidae Mealybugs also known as a Vectors of different plant viruses like cocoa mottle leaf virus and cacoa swollen virus.
- Psyllidae Psyllids are the vectors of mycoplasma-like organisms responsible for pear decline and greening disease of citrus.
In order Thysanoptera (Thrips) members of following families serves as a vector and carrier of following diseases.
- Thripidae Flower thrips are suspected of transmitting bacterial, fungal, and viral pathogens. Tomato spotted wilt virus, for example, is spread by onion thrips ( tabaci) and tobacco thrips (F. fusca).
In order Diptera (Flies) members of following families serves as a vector and carrier of following diseases.
- Tephritidae Apple maggots, Rhagoletis pomonella(family Tephritidae), are vectors of Pseudomonas melophthora, the pathogen of bacterial rot in apples.
- Anthomyiidae Cabbage maggots, Delia radicum(family Anthomyiidae) spread the fungal pathogen of blackleg (Phoma lingam).
- Agromyzidae Leafminer flies, (family Agromyzidae) in the genus Liriomyza are capable of transmitting tobacco mosaic virus and sowbane mosaic virus.
In order Coleoptera (Beetles) members of following families serves as a vector and carrier of following diseases.
- Chrysomelidae Leaf beetles (family Chrysomelidae) spread more than 35 plant viruses including broad bean mottle, turnip yellow mosaic, southern bean mosaic, and rice yellow mottle. Potato flea beetles (Epitrix cucumeris) spread the pathogen of potato scab (Actinomyces scabies) when the larvae enter a tuber. Corn flea beetles (Chaetocnema pulicaria) and corn rootworms (Diabrotica) are responsible for spread of Bacterium stewarti, the bacterial pathogen of Stewart’s disease in corn.
- Scolytidae Bark beetles (family Scolytidae) are vectors of fungal pathogens in trees. The elm bark beetle (Scolytus multistriatus) infects elms with Ceratocystis ulmi, the pathogen of Dutch elm disease. A similar blue stain fungus (Ceratocystis ips) is spread among pine trees by the pine engraver (Ips pini) and other bark beetles. The pathogen for chestnut blight (Endothia parasitica) is also spread by the Scolytidae.
- Curculionidae Plum curculio, Conotrachelus nenuphar(family Curculionidae), inoculate fruits of peach cherry and plum with Sclerotinia fructicola, the fungal pathogen of brown rot.
In order Hymenoptera (Bees and wasp) members of following families serves as a vector and carrier of following diseases.
- Apidae Honey bees, Apis mellifera(family Apidae), and other pollinating insects spread the bacterial pathogen of fire blight (Erwinia amylovora) as they travel from tree to tree collecting nectar.
- Formicidae Ants, (family Formicidae) and bees spread the pathogen for mummy berry, a blueberry fungus, from stem lesions to fruit as they forage for food.
Insect as a vector and Carrier of Diseases in Human and Animal
There is many insect having medical importance by causing injuries, diseases and also can direct and indirect causes of illness, pain and suffering via stinging, biting, wound or through allergic reactions. There are many household insect pests which are cause annoyance like housefly, ants, cockroach and many are dangerouse for livestocks and other wild animal like tsetse fly, fleas, etc.
The insects are hematophagy which are feed on human and animal blood as well as on body tissues along with transmit deadliest parasite and pathogen. There are some major insects order comprises those insects have medical importance like Diptera (Mosquito, House Fly, Tsetse Fly), Hemiptera (Bed-Bug), Phthiraptera (louses), Siphonaptera (Flae) and Blattodea (Cockroaches).
1-Order Diptera
The following members of this order serves as a vector and carrier of diseases. Bot flies/ warble flies’ larvae serve as endoparasites of human including other mammals. Louse fly’s adult serve as ectoparasites of birds and mammals as a blood feeder. Mosquitoes may also spread yellow fever, malaria, filariasis, encephalitis and other diseases. House flies are cosmopolitan insect pest cause dysentery, cholera and yaws by their mouthparts and feet.
2- Order Hemiptera
The members of the following order serve as vector and carrier of following disease like Bedbug causes chagas disease. Assassin bug is also a blood sucker insect spread chagas disease.
3- Order Phthiraptera
Louse borne diseases are quite common in humans and animals these are following like relapsing fever, transmit epidemic typhus and trench fever, and other diseases like borrelia recurrentis, rickettsia, prowazekii, and bartonella quintana.
4- Order Siphonaptera
This order comprises cat fleas, dog fleas and human fleas and spread murine typhus and bubonic plague.
5- Order Blattodea
This order comprises cockroaches one of the most unhygienic insect of household along with that the vector of many dangerous diseases caused by various pathogens these followings like Typhoid cause by Salmonella Typhi, Polio which cause by Poliomyelitis and dysentery.
Talha Javed, Habel Parwaiz and Tahwar Ali Syed
University of Agriculture, Faisalabad, Pakistan