Table 5. I₅₀ values of malaoxon in the inhibition of esterases from workers of Solenopsis invicta and S. richteri on α-naphthyl acetate (α -NA) and β-naphthyl acetate (β -NA).

Species	Substrate	Colony	I50 (mM, mean ± SE)*
S. richteri	α-NA	6	0.086 ± 0.012 a
		9	0.099 ± 0.004 a
		14	0.142 ± 0.041 a
	β-NA	6	0.159 ± 0.022 a
		9	0.210 ± 0.029 a
		14	0.331 ± 0.060 a
S. invicta	α-NA	284	0.040 ± 0.011 a
		2	0.027 ± 0.008 a
		12	0.047 ± 0.005 a
	β-NA	284	0.308 ± 0.037 a
		2	0.221 ± 0.067 a
		12	0.068 ± 0.001 a

*: Within a species and substrate, means followed by the same letter are not significantly different (P < 0.05).