Jessie caught Wurmple in the episode All in a Day's Wurmple, as did May. Several episodes later, in Which Wurmple's Which?, both Wurmple were temporarily switched, but were returned to their proper trainers by the episode's end. In the episode A Corphish Out of Water, Jessie's Wurmple evolved into Cascoon while May's evolved into Silcoon; Jessie believed hers was a Silcoon as well. Four episodes later, in Seeing is Believing, Jessie's Cascoon evolved into Dustox, while May's Silcoon evolved into Beautifly. While Jessie was at first disappointed that she did not have a Beautifly, she soon came to adore her new Dustox (in the Japanese version, she called it Dokucale-chan on more than one occasion). In the English dub, Jessie has called it Dustox-Dear and when she throws its Poké Ball she has also called it "my dear Dustox".
Dustox was Jessie's primary Contest Pokémon. It was used in the episodes Come What May and Disguise Da Limit. Jessie attempted to enter it in the Rubello Town Contest in A Fan with a Plan, but Jessie did not have a previously obtained Ribbon needed for entry.
Dustox was also Jessie's secondary battling Pokémon. It was usually used alongside Seviper, but it had also been used alone. It appeared to be fairly powerful, but as Team Rocket are the villains, it was usually defeated.
In the episode That's Just Swellow, James used Dustox as his Pokémon in a PokéRinger competition. Dustox defeated May's Beautifly in the competition, but it eventually succumbed to a last-minute defeat when Ash's Taillow evolved into a Swellow.
Using Dustox, Jessie was finally able to win a ribbon in the Solaceon Town Contest in Team Shocker!. Ever since, Dustox has been wearing Jessie's hair-ribbons that she wore in that contest, and is probably still wearing it, to remember Jessie by (see below).
In Crossing Paths, Jessie tearfully told Dustox to go with the others, but, since it was loyal, Jessie had to shatter Dustox's Poké Ball to let it go. Dustox then went to live with other Dustox and start a family.