Shot more cos digital is FREE !!!
I not that skillful so always use tripod, live-view and MF. Shoot only still insects practically all the time. If there's lots of activity in an area (like ants), then compose for a specific spot and use remote, pray n wait for subject to come into area of interest (focus) then fire off.
Bro for mi I uses AF macro mode when i am using LX3 with raynox 202/505. Now even i use it on my Fz30 with 250....
100mm on 1.6 crop is 160mm
The main issue is actually the working distance.
I'll use a Tamron 90 vs Tamron 180 for example here.
Tamron 90, MFD = 29cm to image plane (based on a lens length of 9.7cm, you'd have about 19.3cm of working distance) Note one more important detail, this lens is not IF, so it does extend out when focusing to MFD, your working distance should be much shorter than this.
Tamron 180, MFD = 47cm to image plane (based on a lens length of 17.8cm, you'd have about 29.2cm of working distance)
Thus, most insect shooters tend to avoid wearing white, insect repellant and not to talk too loudly or stomp on the ground too much.
Usually for me, I manual focus the lens to nearest focusing distance and move my camera front and back to obtain the best focused shot
PS : its not easy when very near coz the handshake is magnified with near subjects....