Trialling floral-baited traps to survey flower-visiting insects in tropical crops: Findings from an oil palm case study

Monitoring pollinating arthropods in crop systems can provide important information about pollinator populations and potential yield but can be hampered by accessibility to flowers in some systems, or by the timing of flowering and pollinator visits. This is particularly the case in oil palm, the world's leading source of vegetable oil, where flowering is discontinuous, inflorescences are sometimes many metres off the ground, and pollination is largely dependent on a single insect species—the specialist weevil, Elaeidobius kamerunicus Faust (Coleoptera: Curculionidae). We used oil palm as a case study system to trial a new trap design to selectively survey flower-visitors of insect-pollinated crops. The trap consisted of a pan trap baited with half a male oil palm inflorescence. To assess effectiveness of the trap across different environments, we set pairs of baited and non-baited control pan traps in a variety of habitats in industrial oil palm plantations in Riau, Indonesia. We identified all arthropods collected to order level, with ants separated from other Hymenoptera owing to their distinct ecology, and E. kamerunicus identified to species level. We found a higher abundance of arthropods trapped by baited versus unbaited traps across all habitat types and across all taxa except Orthoptera, with the greatest differences found in E. kamerunicus, non-E. kamerunicus Coleoptera, Diptera and Lepidoptera. The age of inflorescences used in baited traps affected abundances of certain taxa, with 8% reduction in E. kamerunicus abundance, 1% reduction in other Coleoptera and 4% reduction in Lepidoptera with each 1% increase in inflorescence openness beyond 40% open. Most taxa were found in higher numbers in the baited traps. The baited pan traps worked across a range of habitats and present an effective and inexpensive survey method for assessing populations of flower-visiting arthropods and could collect a wider range of flower-visitors than traps baited with more specific attractants, such as estragole, a volatile component emitted by oil palm inflorescences. Similar approaches could be trialled in other insect-pollinated crops.