The Hivemind

The Hivemind refers to the Rada's shared consciousness, which is a naturally occurring psychic phenomenon that occurs in each live Rada, host created or biologically born. It appears as a psychic link thats range is planet wide, each Rada capable of feeling each others presence in it and able to converse at computer speeds mentally without having to move their lips, the conversations carried by thought and intent to deliver it. These mental signatures are capable of addressing each other individually and one cannot hear a conversation he hasn't been invited to, but can ask permission to join the call which often is permitted although not always. 
This mental link does not simply allow conversation, for it also allows the sharing of feelings, memories and even genetic traits which are somehow transported through this link which their bodies can then replicate, allowing for much faster evolution than otherwise possible in nature. The Hivemind allows for nearly limitless potential in what it can accomplish and thus it is a dangerous and beneficial tool for the Rada. Not only are they much closer and intimate as a people than other races as they literally know what each other is thinking and feeling, so they have context many other races lack, thus making arguments usually short lived as understanding and comprehension beats anger with sheer facts and logic. 
However it is not all roses and sunshine either, as malicious Rada can cause ill effects with the Hivemind. With enough influence over it, it can be wielded as a dangerous weapon, doing such things as Mind Control, or erasing or altering memories, it can be used to fake communications and sometimes even someone's elses feelings can be made yours. Although doing any of the ill effects isn't easy as all Rada are psionic, it is still a danger that shows that every power and every method, no matter how anticing or beneficial, has its darker side. 
However the fear of being mentally dominated is not eternal and without choice, for powerful Rada are capable of severing a Rada from the Hivemind as well, this is however permanent so those who want out, must contend with the fact that they are forever removed from the community. 
The Hivemind itself of course also enables the other psionic and psychic abilities of the Rada, including such things as empath, telekinesis, telepathy, mind reading, mind control, and all other powers of the mind, depending on the Rada and their ferocity or lack there of, some of these abilities are all available or none of them are. Although more psychically capable Rada are more common, only the truly powerful are capable of controlling non-rada, although they exist. 
To this day, no species outside of the Rada has been capable of interacting or manipulating the Hivemind as it is such a secular connection that it does not accept and even pushes away other wavelenghts, not allowing in even other psychic entities, although such individuals may still interact with the Rada themselves.

Source

The source of the Hivemind is the original Rada Parasite using a host brain as a radio tower to broadcast a signal with what we could call Broadcast organ which sends out a psychic network that any other signals are able to join and of course each form their own upon coming online, thus the more Rada there are, the more pronounced the effects. 
Another large source of it, is the Great Worm who even further enhances this psychic signal.

Discovery

Much like most of Rada discovery, Bashi realized its utility long time ago on Yaku homeworld when he was creating monsters for the Yaku to fight to accept him.

Related Deity/Higher Power

Igsim

Applied Restriction

Obviously, the Rada cannot utilize the Hivemind effectively if they are the lone Rada on the planet as there is no one to share with or speak to. The only other way to hamper is to sever the Rada from it, disallowing them all the benefits that it gives.