Answer
0.41
Work Step by Step
The bug moves in simple harmonic motion. The maximum KE is proportional to the square of the amplitude. The amplitude is half of the peak to peak motion.
$$\frac{KE_f}{KE_i}=\frac{0.5kA_f^2}{0.5kA_i^2}=(\frac{2.25cm}{3.5cm})^2=0.41$$
The KE changed by a factor of about 0.41.