Integrated pest management systems for cotton are now being developed that place a greater emphasis on beneficial insects (Mensah and Harris 1994, Murray et al. 1994). The development of food sprays and the planting of lucerne strips has shown that effective populations of beneficial insects can be maintained within cotton crops (Mensah and Harris 1995). Reductions in pesticide use associated with the introduction of transgenic cotton should also increase the abundance of beneficial insects (at least those not dependent on Helicoverpa) and improve natural control (Dick 1994, Fitt 1994). However, there is considerable scope within the cotton agroecosystem to use other crops as nurseries and/or refuges for beneficial species, and/or as trap crops for Helicoverpa and other pests. Such nursery crops or refuges could be sown in strips through cotton fields, in a similar way to that proposed for lucerne, to attract beneficial species and/or trap pest species. The advantages and disadvantages of various crops in such a system have not been fully investigated. The nursery crop approach relies on there being sufficient beneficial insects within the wider cropping system to colonize the nursery crops in the first place and perhaps recolonize it during the season if pesticide application or drift eliminate populations in the nursery crop. However, we understand very little about the origin and dynamics of beneficial insect populations outside the cotton crop. Where do beneficial species originate and what happens to their populations when the cotton crops disappear? Which natural habitats or crops generate most beneficials?