Answer:
By a factor of 4
Step-by-step explanation:
Consider a simple capacitor instead of the whole story to simplify the problem.
Work done in separating charges = Energy stored in the capacitor (assuming no energy loss happens)
And we know,
Energy stored in the capacitor (E) = VQ/2
and Q=CV
where V= potential difference
Q = charge stored
C = Capacitance
We get, E =

and we know Capacitance (C) = εA/d
A = surface area , ε = permitivity, d = distance between two plates
By the above equation C remains constant for gecko for what ever charge as ε depends only on material.
So you get, E ∝

So charge increased by two gives the energy required to rise by factor of 4