I don’t usually have a problem with ants eating my lures, but I do have to contend with Gisborne cockroaches and tree weta. I do have a few suggestions for things to try, though.
To tackle ants, I highly-recommend applying white vinegar to your lures, by either spraying them or dunking them for a second or 2. The coating of acid appears to deter insects until the vinegar evaporates, and the smell might overpower their senses.
I don’t have any problems with invertebrates, but I doubt that they would like vinegar, either.
In addition to repelling insects, the predators here love vinegar, so it’s worth trying it for that reason alone. I’ve sprayed WV on peanut butter, Nutella, BBQ sauce, egg mayo, etc. and a number of meat lures, and it appears to enhance their appeal. I have a small spray bottle that I take with me to apply to fresh lures and give existing lures another dose. I also spray the entrance of DoC tunnels with it and the lure area.
In wet weather, the acidity of vinegar delays the growth of mould, so it can make a big difference, depending on how frequently you’re able to check your traps. With something like peanut butter, I probably get an extra 24-36 hours before it’s colonised by mold.
Don’t spray vinegar on any metal surfaces that aren’t stainless steel, because it will rust them.
Something else to try is Goodnature’s range of lures. I’ve been using them for 5 years now, and I have yet to find insects or invertebrates eating them. I’ve trapped hundreds of predators with the lures, on their own or paired with others, and they’re an easy, cost-effective way to lure a lot of traps. The possum lure also traps rats, BTW.
The blood lure, especially, has been very good in/on my snap-traps. The downside is that the texture of the lures makes them easy for predators to eat, so I’ve been putting a chickpea on top of the lure inside the bait cup of my T-Rex traps. Rodents like chickpeas, but they like the blood lure a lot more, so I’ve trapped dozens of rodents, big and small, attempting to remove the chickpea, which causes enough disturbance to trigger the trap. Placing a chickpea on top of PB, Nutella has also proven effective, because it gets stuck on top. Nibbling on the very hard chickpea is risky, and so is trying to steal it or move it out of the way. I’ve found a number of rats with a chickpea stuck in their mouth.
The gecko hasn’t been seen or heard again. I’ve done intensive trapping on our property, and planted a lot of native plants, so the geckos have enough food that the odds of me trapping one are probably close to zero, but it can’t hurt to ask fellow trappers.
A very good lure to try is tallow, but insects will eat it, unfortunately. It takes the insects and mice here a lot longer to eat than the other lures you use, due to its texture. Once again, a spray of vinegar will help.
Good luck trapping!