Auto focus would explain why your backgrounds are sharp but some parts of the insects are a little on the soft side. AF auto selects the best target for focusing which can be different from your intended subject.

I virtually always use manual focus, even when not using a tripod. It can take a fraction longer to manually focus but I am sure that the parts which I want to be sharp are correctly focused.

My camera settings average around 1/160 to 1/200 and an aperture of F11 to F14 when using flash and sometimes a little faster on the shutter when not flashing.