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Go back now that you know how to open the force field. Scan the Hive Code Terminal and use it, enter the code from the Monolith and the force field will drop.Return to Melvin and he'll ask you to get some gold bugs. When he has them, he'll let you inside the throne room. After this, the Hive Main Door will open.
You need only 10 gold bugs, but there are more than 10 inside the Hive. There's one in the room with you and Melvin. Second bug is at the side cavern, there's a crystal you should shoot with Havoc Gloves at close range. Third and fourth are on the path near the force field. Fifth is by the conveyor belt. Near the Main Door, there are some stuff you can disassemble to grab the sixth bug. Seventh is near the Monolith Component up ahead. Eighth and Ninth are close the aid station. Scan the Elevator Generator and the Hive Security Scanner. Tunnel underneath the scanner and step on the red circle to deactivate it. Tenth bug is there. Once you have all 10, return to Melvin. Melvin will head down and you'll need to follow him. Scan the Monoliths along the way to grab the code. Once you're near the Hive Throne Room, there's a Transmogrifier and a new thing to scan, the Hive Egg Machine. Make what you can at the Transmogrifier and prepare for a boss battle. Talk to Melvin to open the throne room door.