Predation Pressure on Invertebrate Sentinel Prey Depends on Distance to Forest Edge and Seasonality in Kenyan Tea (Camellia sinensis) Plantations

Tea is a global commodity, and due to its way of preparation pesticide residues cannot be tolerated. This underlines the importance of non-chemical pest control. Kenya is the third largest global tea producer but the potential of natural enemies against tea pests is unknown. We used artificial caterpillars made of non-drying green plasticine to quantify attack rates by predators on tea canopies at different distances from plantation edges and in the nearby native forest during the wet and dry seasons in three tea-growing mountain regions of Kenya, Kericho, Gatamaiyu and Kakamega. The artificial sentinel caterpillars were readily attacked by arthropods, birds, and sporadically by small mammals. During an exposure time of 24 h, the overall attack rate was 25.0%d^-1. Natural enemy activity was higher in the dry (35.3%d^-1) than in the wet (16.7%d^-1) season. The highest predation pressure was measured in the native forest (41.7%d^-1) and gradually decreased with increasing distances into the tea plantation (to 8.3%d^-1 at 40 m from the edge). The rate of decrease from the forest edge towards the centre of the tea plantation was steeper for birds than for arthropods, indicating that birds were more reluctant to use this habitat. The potential for natural pest control in Kenyan tea plantations is high, but planting native trees is recommended especially if bird activity inside tea plantations is to be encouraged.