Umbonia crassicornis generally use a substrate-borne form of communication.
Allowing the parent and nymphs to communicate through chemically triggered vibrations.
The main reason for these vibrational signals is in response to predators like the vespid wasp (one of the nymph's main predators).
It is also seen that vibrations can be used to communicating within the brood.

These signals act as an anti-predator response and alert the mother to the presence of danger, the mother, however, will only respond to the brood if their signaling is synchronized, so the whole group has to work together to alert the mother otherwise she will not respond.
To achieve this, young must respond immediately after hearing the signal from another nymph for their response to be synchronized.
In doing this, the brood is deciding whether a threat is worth risking the mother attacking and possibly being removed from the congregate.
If all the young in the brood decide the threat is worth the risk, then a synchronized signal is created.
If only a few nymphs call about the disturbance then the synchronization won't be achieved and the mother will not respond.
If the mother still can not find the threat after the young have signaled her, she will respond 'asking for help' to find the predator.

Though the nymphs are a good detector of predators, no one nymph can predict if the threat has left or not due to each individual only being able to scan a small area.
The only good predictor that the predator has retreated is the mother.
After they have deterred the threat the mother will send out a signal to her young to tell them they are safe.
Umbonia crassicornis generally use a substrate-borne form of communication. Allowing the parent and nymphs to communicate through chemically triggered vibrations. The main reason for these vibrational signals is in response to predators like the vespid wasp (one of the nymph's main predators). It is also seen that vibrations can be used to communicating within the brood. 
These signals act as an anti-predator response and alert the mother to the presence of danger, the mother, however, will only respond to the brood if their signaling is synchronized, so the whole group has to work together to alert the mother otherwise she will not respond. To achieve this, young must respond immediately after hearing the signal from another nymph for their response to be synchronized. In doing this, the brood is deciding whether a threat is worth risking the mother attacking and possibly being removed from the congregate. If all the young in the brood decide the threat is worth the risk, then a synchronized signal is created. If only a few nymphs call about the disturbance then the synchronization won't be achieved and the mother will not respond. If the mother still can not find the threat after the young have signaled her, she will respond 'asking for help' to find the predator. 
Though the nymphs are a good detector of predators, no one nymph can predict if the threat has left or not due to each individual only being able to scan a small area. The only good predictor that the predator has retreated is the mother. After they have deterred the threat the mother will send out a signal to her young to tell them they are safe.
Umbonia crassicornis