*** This has to be done all at one time not different infestation at different times which is really easy, also on your own properties on colon estates*****
Just as mention in the other solution.
Geenfeilds, no computers and moved HQ.
Set your HQ on upper colon estates.
Then buy a different area and build the lumber yard. *Dont build the Lumber yard on the colon estates*
Build 3 lvl one houses on colon estates.
***** Dont move in tenants, leave the houses vacant****
This will cause a cockroach infestation
***** now fast forward the time to max****
then watch the cockroachs go to house to house infesting one another. You should get the achievement at this time.
Let me know if something needs to be improve in a comment before giving me a thumbs down and I will fix it and give you credit. Thank you, happy achievement hunting.