Pollination Biology of Theobroma and Herrania (Sterculiaceae) — III. Steam-Distilled Floral Oils of Theobroma Species as Attractants to Flying Insects in a Costa Rican Cocoa Plantation

Steam-distilled floral oils (essences) from several species of Theobroma (Sterculiaceae) (T. cacao Linneaus, T. simiarum Donn. Smith, T. mammosum Cuatr. & Leon, and T. speciosum Willd.) were tested using McPhail traps, in an abandoned Costa Rican cocoa plantation to determine their levels of attraction for flying insects. In each of the three bioassays (two successive dry seasons and one intervening rainy season), the traps were inoculated with floral scents at 1, 10, and 100 ppm, while controls were inoculated with a 10% solution of chloroform solvent in distilled water. Of a total of 223 Diptera captured in all three bioassays, only 5% were found in the controls, indicating attraction to the floral oil. About 72% of all Diptera captured were Cecidomyiidae, of which three species, Mycodiplosis ligulata Gagne, Aphodiplosis triangularis (Felt.) and Ledomyia sp., comprised 59% of the total. Eighty-eight per cent of all midges captured were females. Only 7% of the total were known cocoa-pollinating midges of Ceratopogonidae, and all of these were females. Sixteen per cent were Phoridae, known pollinators of the allied genus Herrania in Costa Rica. Although the chemical composition of floral oils varies greatly among the species of Theobroma, no discernible differences were found in the attraction of midges to floral oils tested. While floral fragrances in Theobroma species may represent a generalized adaptation for dipteran pollination, small numbers of several species of Trigona bees (Hymenoptera: Apidae: Meliponinae) were also attracted to the floral oils.