Is the yellow ladybug poisonous

No, yellow ladybugs are not poisonous.

Specifically, the Asian ladybug beetle (Harmonia axyridis) is one of the insects in question (Coccinellidae family) whose background coloring can be orange, red or yellow. Such bright colors serve to warn potential predators of a distasteful meal. A predator famished enough to go ahead and eat a yellow ladybug would suffer an upset digestion but would not die unless some other complicating factor - such as severe dehydration or pesticide exposure - is involved.