Deterministic modeling of negative cross-resistance strategies for use in transgenic host-plant resistance

Negative cross-resistance refers to a situation in which an insect populati on that is tolerant (resistant, virulent) to one insecticide is hyper-sensi tive (avirulent) to a second insecticide and insects hyper-sensitive to the first compound are tolerant to the second. Most research dealing with nega tive cross-resistance has focused on the molecular biology and chemical asp ects of this phenomenon. We explored, from a population genetics perspectiv e, whether negative cross-resistance is feasible in the control of an insec t population. As a first step towards this goal, we used a deterministic ap proach to evaluate different control scenarios and to identify some of the potential limitations of negative cross-resistance strategies. Specifically , we investigated how such approaches could be used in a host-plant resista nce program. Homo- and heterozygous insect fitness influenced the effective ness of the toxins in controlling the insect population. The negative cross -resistance strategy was most useful when the insects' virulence to both ho st-plant toxins was recessive. When virulence was dominant, there were many periods when intervention with an outside (or third) class of compounds, w hich had a different mode of action than that of the negative cross-resista nce compounds, was needed to control the insect population. The greater the number of insect generations per plant generation, in the absence of immig ration or emigration in the insect population, the greater the requirement for intervention with a third class of compound to maintain effective contr ol of the insect population. When the toxins were rotated every insect gene ration, and virulence in the insect was recessive to both toxins, effective control of the insect population was maintained without intervention of a third class of compounds. (C) 2000 Academic Press.