Senior Scientist National Agriculture and Food Research Organization (NARO) Shimada, Ibaraki, Japan
As resistance is driven by the fitness differences between pests with and without resistance genes under a pesticide dosage, the management principles can be broadly classified into two categories: to mitigate the control pressure to allow the susceptible pest strains to survive, or to intensify it to eliminate even the resistant individuals. The former includes the rotational use of multiple pesticides, although it can only delay additively the resistance development in proportion to the number of control measures involved. The latter has been known as redundant killing by multiple active ingredients. It is also the operating principle behind the high dose/refuge (HDR) strategy. In the absence of refuges, higher dose monotonically accelerates the resistance development. If there is a reservoir of untreated population, a single dose level exists that most accelerates the resistance evolution, i.e., a high-dose threshold. Unlike Bt crops, it is difficult to apply a single high-dose insecticide, but a mixture of active ingredients with different MoAs can reach the HDR state. Simulation results show that if the initial resistance allele frequencies are low and a certain portion of the on-farm population escapes from spraying regardless of its genotype, pesticide mixture would delay resistance development. Our analysis suggests the proportion of escaped individuals is around 10% in current field applications, which will be sufficient for the resistance management using mixtures. However, the systemic property of each active ingredient halves the amount of escapement, where the resistance delay might depend on the pre-mating dispersal of insects