Vectors: It is an organism which helps in spreading an infection from one host to another and it does not cause disease itself. Example: mosquito (Anopheles mosquitoes), act as a vector to spread out the malaria disease through transferring the pathogens from infected host to others.

Gregarious pest:  A pest which move with other pests collectively and attacks on crop field are known as gregarious pest and live their life. Example, Locusts attack on crop field in group together with pests.