The following points highlight the top three modes of transmission in insects. The modes are: 1. Mechanical Transmission 2. Biological Transmission 3. Transovarial Transmission.
Mode # 1. Mechanical Transmission:
This may be indirect. The simplest method is the indirect mechanical transmission where the insects take up the role of passive carriers of diseases. They only pick up the organisms causing disease, from the bodies or the excretions of man or animals and deposit them on food. The commonest carriers are the house flies and roaches.
A step further towards the specialization of transmission may be found in the direct mechanical transmission method. Here, the insect picks up the germs from the body of diseased individual and directly injects them into the blood of other animals through the skin or sores or wounds.
Tsetse flies and certain others transmit the blood diseases namely, Anthrax, Fowl pox and trypanosomes causing some animal Trypanosomiases. The flies that feed on wounds transmit skin or eye diseases ‘oriental sores’, ‘trachoma’, etc. The organisms of all these diseases do not survive for more than a few minutes to a few days in the vectors.
ADVERTISEMENTS:
Organs concerned with transmission:
i. Mouth parts:
a. Biting:
In the insects transmitting diseases, specially in plants, the mouth parts are modified for biting.
ADVERTISEMENTS:
Example: Thrips.
b. Sucking:
In mosquitos, the mouth parts are modified for sucking. Generally, the hypo pharynx and epipharynx undergo modifications. The mandible is lost or rudimentary. In fleas, hypo pharynx, mandible and maxillae are modified to form piercing organs.
Another variety of sucking modification is found in the sponging type, where the organ concerned is popularly known as proboscis.
ADVERTISEMENTS:
Example: House fly.
ii. Legs:
In house flies, legs carry the germs of diseases.
iii. Antennae:
The antennae serve the same purpose in the insects in general.
iv. Body:
In house fly, the body as a whole acts as the carrier.
Mode # 2. Biological Transmission:
When multiplication or cyclical changes or both take place within the body of the insects, it is known as biological transmission. It may be propagative, cyclopropagative, cyclodevelopmental, and transporting.
Mode # 3. Transovarial Transmission:
This means transmission of disease through infected ovary and the egg, often referred to as hereditary transmission. The infection is effected specially by mites and licks. Insect-borne infections are extremely insignificant, although some virus infections may be significant.