A new species of Diadiplosis, D. abacaxii sp. nov. (Diptera: Cecidomyiidae) is described and illustrated based on specimens collected in association with the pineapple scale insect pest Dysmicoccus brevipes (Coccoidea: Pseudococcidae) on Ananas comosus (L.) Merr. var. comosus (Bromeliaceae) in Espírito Santo, Brazil.