The Ultra-Bitter Spray is a very useful spray in Pikmin 2 which can petrify almost any enemy, including bosses for a short period of time. During this time the enemies can be attacked, usually inflicting plenty of damage except in a few rare cases with some of the bosses. If Olimar defeats a petrified enemy before it can revert back to its normal state, it will leave behind a drop of nectar or perhaps a dose of Ultra-Spicy Spray or Ultra-Bitter Spray. In order to get more Ultra-Bitter Sprays, seek out plants in the overworld that bear purple berries and have Pikmin harvest them and bring the berries back to your rocket. Ten purple berries make one dose of Ultra-Bitter Spray. Purple berries are decidedly rare, but the best place to find them is Perplexing Pool. Another option is to look for Doodlebug in certain caverns. If you flip over a doodlebug three times, it will leave behind two Ultra-Bitter Spray doses along with nectar. Doodlebugs are also rare, and the best place to find them is Frontier Cavern. A trio of them live among the Bulborbs on the first sub-level.
Patrolling enemies like Spotty Bulbear and Gatling Groinks are harder than most because they are much more difficult to trick or ambush and have lots of power and stamina. This spray helps very much in defeating them, as well as Fiery Bulblaxes. Another good use is when Olimar is completely surrounded by many enemies and is about to be obligated. Olimar must fire off a bitter spray and run out of there as fast as he can.