Lesko is a somewhat befuddled and misguided scientist whose experiments on ants have proven disastrous for Grayditch. Deep inside Marigold Metro Station, he carries out his research, completely oblivious to the destruction that his fire ants have caused. He has little patience for anything beyond his scientific acumen and dismisses his failures as only temporary obstacles on the road to success. While his motivation is to save the wasteland, his methods are in fact destroying it.
Until the quest Those! is completed, Lesko can be found deep underground in the Marigold Station. He will usually be in his laboratory outside the hatchery, or he might flee a short distance into the hatchery itself.
Lesko will not return to his shack until Those! is fully completed. This means you must also find a home for Bryan (or refuse to do so) and receive the experience points for this quest before Lesko will return to his shack.
Those!: Doctor Lesko requires the player's help to regain control of his experiment. If the player has a high enough Science skill and Intelligence, an additional dialogue option appears when asking Lesko about his experiments. When the Science option is chosen, Lesko reveals that he has been using FEV in his experiments. An additional dialogue option will also appear if the player has chosen the perk Entomologist, which upsets the doctor slightly.
Nectar Collecting for Fun and Profit: After completion of "Those!", Lesko will pay for samples of fire ant nectar. Be aware that entering Doctor Lesko's shack will be considered trespassing, even though you might have to enter it to give him some nectar. Stay there for too long, and both the protectron and Doctor Lesko will become hostile to you.
It is evident that Lesko feels little to no remorse about the lives his experiments have cost. He supports the Lone Wanderer's decision to find Bryan Wilks a new home, but only because he will no longer be pestered by Bryan's questions.
Lesko can sometimes be killed by fire ants if you leave both doors to his office open. Close them after speaking to him to ensure he is not killed before you have completed his quest.
If you don't select the extra payment option during the quest, you cannot obtain Lesko's lab coat. Killing him after completing the quest will net nothing but a loss of Karma. The clothing he has on him is just a normal lab technician outfit.
Be warned if you decide to wait and get the perk later, for example, to use the bonus to Perception or Strength to get 10 in all attributes, if you complete 'Those' when the Doctor has returned to his shack, you are no longer able to get the perk as the speech option is now gone.