Susceptibility management of Lygus in the west

Lygus management has become more important in Arizona cotton in the last few years due to a series of factors. Two of these factors, widespread availability of insect growth regulators (IGRs) for whitefly control and transgenic 'Bt' cotton for lepidopteran control, have resulted in a drastic reduction in the number of Lygus-active insecticides sprayed in our cotton systems (see Ellsworth, this volume). In 1995, an average of 12.5 foliar insecticide sprays for all insects (1.26 directed at Lygus) were made in Arizona cotton, many of which had some degree of Lygus activity (see Williams, 1996-1998). In 1997, this was reduced to 5.33 applications (2.10 directed at Lygus), and about 0.5 of these were IGRs which have no Lygus activity. This reduction in use has effectively opened a window during which Lygus can cause damage and promoted this pest to major status. Another factor that has also raised the prominence of this pest in our landscape is the substantial increase in alfalfa acreage, including some seed alfalfa, in Arizona. When any 'old' pest comes into prominence, there are often complaints about insecticide spectrum, residual, and performance. In addition, in spite of the reduction in overall foliar insecticide use, resistance to insecticides is an ever-present threat which may be present and may or may not be impacting insecticide performance in each area of production (Dennehy, this volume; Pacheco, this volume). Whatever the causes that have elevated Lygus pest status, we must consider susceptibility management of this and all other pests when constructing sustainable integrated pest management strategies. While this paper was invited to address the problem over the entire West and over multiple crops, my focus will be on Arizona cotton only. The necessity of this approach becomes obvious after considering the large differences in management and chemical efficacy between California (Godfrey, this volume) and Arizona (Pacheco, this volume). Nonetheless, the tenets of susceptibility management are equally relevant across all regions and all crops. They are in their simplest forms: 1) limit insecticide use to the lowest practical level; 2) diversify insecticide use patterns; and 3) partition insecticides among crops and pests such that modes of action are segregated as much as is practically possible.