Eriophyoid mites are commonly associated to palm trees, although few of them have been reported causing economic damage to those plants. One exception is Retracrus johnstoni Keifer, a pest of Bactris gasipaes Kunth, plant used for palm heart production. R. jonhstoni is frequently found in large numbers on Arecaceae in southeast Brazil. The biology of this mite was studied under laboratory condition. Sections of leaves of the palm tree Syagrus romanzoffiana (Cham.) Glassman, with ca. 15 leaflets, were kept alive by maintaining their bases in distilled water. Ca. 20 field collected adults of R. johnstoni were transferred onto each leaflet for oviposition. After 24h, mites were removed, leaving only one egg laid. Once a day, the eggs and the subsequent stages were examined to determine the life cycle, oviposition rate and survivorship. Each immature stage of R. johnstoni lasted ca. seven days, corresponding to ca. 20.5 days for immature development. The sex ratio was ca. two females per male. Total fecundity was slightly over five eggs per female. Immature and adult mites secreted a layer of white material, which covered their bodies. Spermatophores of R. johnstoni resemble those of other species in the same superfamily, and consist of a head of ca. 6 x 6 µm onto a base ca. 6 µm long. Leaflets show dark spots on the lower surface and yellowish spots on the corresponding regions of the upper surface. Leaf spots become progressively larger and coalescent, and the leaf dies and falls prematurely.
Biology; Eriophyoidea; Arecaceae
