Best lens for nikon d5100 for insect photography?

What is the best lens to use with nikon d5100 to photograph insects

There's many macro lens but I prefer this one for beginner Nikon 18-105mm f/3.5-5.6 AF-S DX VR ED Nikkor Lens for Nikon Digital SLR Camera it's great for portrait too

I think it might be best for you to buy a set of extension tubes and use that instead of a different lens.

Now for the real answer…

You want a true macro lens with 1:1 reproduction. For insects, you want some distance between you and the bug.

The best lens for this for your camera is the Nikkor micro (Nikon macro) 105 mm AF-S lens.

Ein MM's recommendation is NOT a macro lens - which is what you need.

I recommend the Sigma 50mm f2.8 or the 105mm f2.8 - both are true (1:1) macro lenses.

I have the Siggy 50mm on a D300 - these are typical shots with it;

It also makes a great portrait lens.

A 50mm f/1.4 mounted on a bellows or you could get one of those 40mm f/2.8 Micro lenses.