Maintenance of ladybeetle diversity across a heterogeneous African agricultural/savanna land mosaic

Abstract

The importance of agricultural land for maintaining indigenous biodiversity is an important contemporary issue. A large agricultural estate in Swaziland, which is a mosaic of citrus orchards, exotic tree windbreaks, indigenous riparian vegetation and savanna was investigated. The distribution of larval and adult coccinellids within the habitat types, and the relative influences of temperature, relative humidity, ground insolation and prey presence was assessed over a 2-year period. The highest coccinellid densities and species richness occurred within the orchards. Riparian habitats on the boundaries of the estate were closer to the orchard habitat in species composition than was the natural savanna. Not surprisingly, the presence/absence of prey was the most important variable which determined coccinellid distribution and density in the agricultural landscape. Relative humidity, temperature and ground insolation had no significant effect on coccinellid densities. Some species, such as the exotic Cheilomenes lunata, and the indigenous Scynmus sp. and Nephus sp. were widely dispersed and occurred in all habitats, while the economically important but exotic species, Rodolia cardinalis was only within the citrus orchards. Overall, the coccinellid assemblage was not a good indicator of habitat type. Nevertheless, a variety of habitat types (i.e. a heterogenous landscape) appear to be essential for the survival of most coccinellids. Indeed, the heterogeneous agricultural and natural land mosaic provides maximum plant diversity and hence coccinellid diversity, thus increasing the potential for natural control of pest prey species in the orchards, while at the same time maximizing survival of indigenous coccinellids.