Floral biology and flower visitors of cocoa (Theobroma cacao L.) in the upper Magdalena Valley, Colombia

Abstract

Cocoa (Theobroma cacao L.) is an important crop, but yield is generally low. Improving yield requires detailed understanding of the reproductive ecology, especially the pollination system and factors determining pollination success, such as proximity to natural areas. Since the 1940s biting midges have been proposed as the pollinators of cocoa flowers but this idea has recently been questioned in various studies. We observed cocoa flowers and their visitors during anthesis, we compare cocoa flower visitors during the day and night and also in plantations connected and disconnected to natural forests. Observations of flowers during anthesis revealed that cocoa flowers are protandrous, open at night, persist for three days and are receptive only during the day. A diversity of insects visited flowers throughout 24 h. In general, insect visitors were more diverse during the day and in plantations connected to forests compared to those not connected to forests. Fifty five percent of the total insect species visited the cocoa flowers at night, all insect species visited cocoa flowers in plantations connected to natural forests and 62.5 % of those visited cocoa flowers in plantations disconnected with forests. Hymenoptera and Diptera were the main visitors and a total of eleven insect species carried cocoa pollen grains. Among those, two species of biting midges (Ceratopogonidae flies) and two species of stingless bees (Meliponini bees) were the most common. While biting midges were the most common visitors, the stingless bee Tetragonisca angustula carried large cocoa pollen loads and interacted with both the male and female parts of the flower. Ants also visited cocoa flowers, mainly at night. The most common visitors of cocoa flowers in cocoa plantations in the upper Magdalena Valley in Colombia are diurnal biting midges and stingless bees, but also nocturnal ants, suggesting that the pollination system of cocoa flowers may be locally less specialized than previously thought. Future research should investigate the effectiveness of various insect groups as pollinators.