Foraging trip duration and density of megachilid bees, eumenid wasps and pompilid wasps in tropical agroforestry systems

1. Most animals have to bridge some distances in space and time to provide all resources necessary for survival. Little is known about how the local and regional management of tropical agroforestry systems, differing in the availability of food resources and suitable nesting sites, determine foraging trip duration and density of bees and wasps (Hymenoptera Aculeata). 2. In this study, foraging trip duration and brood-cell density (in trap nests exposed for a 15-month period) were analysed for three species, which represent three guilds in 24 agroforestry systems in Central Sulawesi (Indonesia): the pollinator Heriades sp. aff. fulvescens (Apidae), the cacao caterpillar-hunting predator Rhynchium haemorrhoidale umeroatrum (Eumenidae) and the spider-hunting predator Auplopus levicarinatus (Pompilidae). The agroforestry systems were characterized by plant species richness, blossom cover of herbs, light intensity and distance from the nearest natural forest. 3. The correlation of foraging time to bee and wasp density showed the relative importance of food and nest-site availability for the pollinator and the spider-hunting predator, because both parameters are correlated with light intensity in the agroforestry systems. In contrast, foraging time and nest density of the eumenid predator were not correlated because of the distance between high quantities of food resources (in sites with dense cacao plants) and nesting sites (in adjacent natural forests). 4. The eumenid response to local and regional agroforestry management illustrates that species may survive only in landscapes that permit access to a multiple set of resources. Accordingly, habitat evaluations using only foraging time may lead to wrong conclusions, as key drivers of population dynamics may not be inside but outside the local systems, emphasizing the need for a landscape approach.