Harmful Insects

Harmful Insects

Various insects cause considerable harm to human as vectors of pathogens, as pests of crops, vegetables and stored grains.

Common are mosquito, housefly, bed bugs, head and body lice etc.

Mosquito (gnats)

Belongs to order Diptera. 3 genera are Anopheles : vector of malaria parasite; Culex - vector filaria worm and dengue. Aedes - vector for virus of yellow fever, dengue fever.

Female is sanguivorous (sucks blood), while male is herbivorous.

Antenna in male is bushy (plumose type) while in female is in hairy (pilose type).

Mouth parts piercing and sucking type with total 9 parts; labium is dorsally open tube-like forming main part of proboscis.

Mandible and maxilla as long stylets are the piercing organs (absent in male)

Labrum long blade-like form list over the open part of labium.

Hypopharynx long double edged sword like forms salivarium.

Maxilla is represented by only galea (endopodite).

One pair of maxillary palp (exopodite) remain outside the proboscis.

Wing only one pair, the second pair is highly reduced small, blade-like called balancer (or haltere).

Aedeagus (or penis) in male as modified sclerites of 9th and 10th abdominal segments is specialized for copulation while flying.

Life cycle

Eggs are laid in water and also in damp places

Blood meal is urgently required for the female after copulation, hence becomes attacking

Development is indirect, takes about 3-6 days, larva and pupa stages (holometabolous) are well developed.

Larva (wriggler)

Aquatic, herbivorous and moves by contraction of body muscles.

Antenna and compound eye are well developed. Mouth parts biting and chewing type, well developed bristles (as tuft) help in floating.

Pupa (tumbler) is comma shaped, very active but non-feeding stage.

Body is divided as cephalothorax and abdomen with respiratory trumpets and tracheal gills.

Imaginal disc are formed as the buds of adult (imago) structure.

Control of Mosquites

Destruction of breeding ground, physical killing, cleanliness etc.

Chemical control is the major means to control mosquito

As repellant :

Fumigation : Fumes of castor, oil cakes, sunflower straw is used in villages; fumes of mosquito coil or mats are also used.

Mosquito ointment (odomos) is also effective repellant

As killer (poison) :DDT, DDD, BHC, pyrethrin, kerosene, petroleum oil, paraffin, carbon pthalate, diethyl pthalate are effective to kill the mosquito at both larval and adult stages.

Layer of petroleum oil on the water surface is effective in following way :

• Oils reduces surface tension hence larva cannot remain suspended along the water surface, and cannot breathe.
• Oil enters into spiracles and blocks the entire tracheal tube causing suffocation.

Biological Control

It is scientific method suitable for environment and ecology; other organism or animals are used to control the mosquito e.g.:

• Dragon fly : Its adult feeds upon adult mosquito and the nymphs (naiads) feeds upon the larva.
• Fishes : stickle back (minnow), Gambusia, Channa, Anabas and some cat fishes, feed upon the larvae.
• Wall lizards in houses feed upon mosquito to a large extent
• Recently genetically engineered bacteria have been produced in Singapore, the mosquito larvae dies when feeds upon these bacteria.

Other Harmful Insects

Blood sucking ectoparasites

• Bed bug - Cimex,  carrier of typhoid, cholera, T.B, and other diseases
• Rat flea - Xenopsylla, carrier of plague virus and bacteria
• Body and head Louse - Pediculus humanis, carrier of various disease.
• Sand fly - Phlebotomus argentipes, vector of Leishmania donovani causing Kala-azar.
• Tse-tse fly - Glossina palpalis, vector of Trypanosoma gambiense causing sleeping sickness.