The effectiveness of Tripzell 20 SC (Fipronil) was evaluated in the reduction populations of Solenopsis sp ants in pineapple plantation in Matas Farm – HODA, located in the Caribbean of Costa Rica. Ants are important because by their symbiosis with Dysmicoccus brevipes (cochinilla) develop phytosanitary problems in fruit at the harvest time of pineapple. The treatment consisted in the application of Tripzell 20 SC at a dose of 0.375 mL per liter of water in mix with Quizalofob and Diuron. The manual application was focused at borders of plantation and fallows with terrestrial equipment, comparing the effect of the application before and after of use Fipronil. The evaluation did at 45 and 60 days after the application (daa), by sampling on traps with placed every 10 linear meters. With an evaluation scale where 0 = no ants, 1 = less than 20 ants, 2 = between 20 and 50 ants and 3 = more than 50 ants per trap, the degree of ants infestation of the treated area was determined. The application of Tripzell 20 SC significantly reduced the populations of ants, going from indexes of 2,3 on fallow edges to 0,6 at 45 dda and 1.0 to 60 daa, while on plantation borders, the reduction algo was significant: 1.0 to 0,0 at 45 daa and 0,6 at 60 daa.