Bleargh! I hate that room!
Step 1:
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×Enter from the east, and lure as many roaches into the corridor as possible. Kill them. (By going back and forth hitting the orb.)
Step 2:
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×Get as many roaches as you can into the bottom left boundary - be careful not to trap any of them behind it so you can't get to them
Step 3:
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×Hit the orb to the left of the one which operates the corridor. Run back and forth between the inside of the two closed boundary areas to try and arrange the roaches in the top boundary. - I hate this bit, it's just awkward.
Have fun!