Heliothis spp. have two main attributes which give rise to their pest status and make them difficult to manage (see Fitt this volume). Firstly both species exploit a wide range of host plants in addition to cotton, including most crops (eg. sorghum, sunflower, maize, and many others), and many weeds. Many of these hosts are extremely important in the seasonal dynamics of Heliothis populations and past research has identified the sequence in which they are used from spring through to autumn. These hosts represent the source of many of the moths which colonise cotton crops, but at present we have no way of estimating the relative importance of intercrop movement in the dynamics of Heliothis on cotton or the contributions of different crops to the local population. The second important attribute is that Heliothis moths are highly mobile.