Sensitivity to incomplete lethality or competitiveness. We examined the impact of varying levels of lethality (penetrance) of the late-acting lethal (RIDL) system (a, b) or reduced competitiveness of the RIDL larvae (c, d) at release ratios of 2 (panel a) or 7.5 (panel b) with β = 1 and P = 1.31, equivalent to Fig. 1a and b respectively. Apart from the new parameters L and C (below), all other parameter values and assumptions about density-dependent mortality, relative mating competitiveness and release ratios are as for Fig. 1. (a, b) In each case, the lethality, L, associated with inheritance of a single copy of the RIDL construct was examined at values of L = 1, 0.95, 0.9, 0.8, 0.7 and 0.5. At L = 1, the outcome is identical to that of shown in Fig. 1 (red lines in Fig 1a, b). (c, d) The contribution of larvae carrying RIDL constructs to the overall density-dependent mortality experienced by all larvae in the generation was examined by varying a competitiveness scaling factor, C, between 1 (i.e. RIDL larvae are as competitive as the wild type and contribute equally to density-dependent mortality) and 0 (i.e. RIDL larvae contribute nothing to density-dependent mortality – this scenario is equivalent to an early acting conventional SIT system). C = 1 and C = 0 therefore correspond to the red and blue lines, respectively, in Fig. 1a,b.