A Bugs Life Codes -

Level select:
Go to the ant hill from the main screen. Then, hold C-Up + C-Down + C-Left + C-Right + Z and press R. An arrow pointing to the right will appear at the bottom of the screen to confirm correct code entry. Scroll the screen in that direction to access any level.

Invincibility:
Hold Z + R + L when the level description appears at the start of a level. Note: The invincibility only lasts for the current level.

Unlimited lives:
Return to training level and find the letters to spell "FLIK" to gain a bonus life. Repeat this to obtain as many lives as needed before resuming the regular game.