The SF values of the PAEO and pyrethroid combinations evaluated were higher than those obtained by GIST & PLESS (1985) when combining cypermethrin with PBO (SF between 1.31 and 3.1) and by BERNARD & PHILOGENE (1993) when combining gamma-cyhalothrin (SF = 3.5) with PBO, as well.
Angular coefficient values of the dose-mortality curves were considered low for topical contact in both synergistic combinations of the PAEO with the four insecticides evaluated.
As a result of this response homogeneity, reduced selection pressure for this larval population's resistance is expected for the PAEO synergistic combinations with alpha-cypermethrin and beta-cypermethrin via topical contamination.
The effect occurred through residual contact, expressed by the [LC.sub.50] of the synergistic combinations of the PAEO with the insecticides evaluated, and also indicated sufficient toxicity for promoting S.
For this contamination pathway, there were significant SF values for the two PAEO sub-doses combinations with beta-cypermethrin (SF = 9.05 for 1/2 [LC.sub.50] PAEO and 0.5 for 1/4 [LC.sub.50] PAEO) and fenpropathrin (SF = 34.05 for 1/2 [LC.sub.50] PAEO and 49.77 for 1/4 [LC.sub.50] PAEO) (Table 2).
The SF values were insignificant for the synergistic combinations of the alpha-cypermethrin with 1/2 of the [LC.sub.50] of the PAEO and for the two synergistic PAEO combinations with gamma-cyhalothrin via residual contact.
Contrary to what was expected, higher SF values were observed for the combinations of PAEO used at 1/4 of the [LC.sub.50] or [LD.sub.50] and/or lethal doses than at half of the respective [LC.sub.50] or [LD.sub.50] for most of the insecticides via both contamination pathways evaluated (Table 2).
However, the angular coefficients of the insecticides considered individually for the alpha-cypermethrin (1/1 [LD.sub.50] PAEO) and beta-cypermethrin (1/2 and 1/4 [LD.sub.50] PAEO) combinations were even lower (Table 2).
As a result of this response homogeneity, corroborating previously obtained results for topical contact, reduced selection pressure for this larval population's resistance is expected for the synergistic combinations of PAEO with alpha- and beta-cypermethrin.
As an additional tool for managing resistance to insecticides, PAEO has the potential to reduce commercial insecticide doses and PBO in particular (WALIA et al., 2004).