Water Repellent EditThis version of Repellent is crafted by surrounding standard Repellent with Hydrofuge in a Crafting Table. Its sole use at this time is to craft Water Striders, by surrounding a pair of Reinforced Exoskeleton Boots.
Insect Repellent EditA rather specific item with quite a useful function, Insect Repellent is crafted using 5 Iron Ingots, a Wooden Button and a (fluid ounce?) of Repellent. Once crafted, you will receive 9 cans of Insect Repellent.
How is this useful? It does what it says on the can (sorry, couldn't resist!). Right-click on a block whilst holding a can of Insect Repellent to spray that block, coating the top with Insect Repellent. This acts as a hard barrier to any arthropod that attempts to step through it.
However, unlike bug spray in reality, this literally just repels; it will not harm any arthropods, only prevent their passage.