Table 3. Efficacy of Bt toxins Cry1AbMod, Cry1Ac and Cry2Ab singly and in combinations against a resistant strain (BX-R) of pink bollworm (see Methods for details).

	Concentration	Mortality (%)a
Toxin set	(µg per ml diet)	Obsb	Expc	Obs - Expd	P e
Cry1AbMod	0.1	12	—	—	—
	1.0	27	—	—	—
Cry1Ac	30	12	—	—	—
	100	35	—	—	—
Cry2Ab	3.0	4	—	—	—
	10	8	—	—	—
Cry1AbMod + Cry1Ac	0.1 + 30	0	22	-22	0.004
	0.1 + 100	42	42	0	1.0
	1.0 + 30	46	35	11	0.37
	1.0 + 100	81	52	29	0.02
	Mean	42	38	4	0.36
Cry1AbMod + Cry2Ab	0.1 + 3.0	23	15	8	0.24
	0.1 + 10	42	18	24	0.03
	1.0 + 3.0	46	30	16	0.16
	1.0 + 10	62	33	29	0.02
	Mean	43	24	19	0.0003
Cry1Ac + Cry2Ab	30 + 3.0	20	15	5	0.54
Cry1AbMod + Cry1Ac + Cry2Ab	0.1 + 30 + 3.0	27	25	2	0.80
	1.0 + 30 + 3.0	63	38	25	0.02
	Mean	45	31	14	0.10

^aAll mortality values are adjusted for control mortality.

^bObserved mortality

^cExpected mortality for combinations of two or three toxins

^dObserved mortality - expected mortality; synergism causes positive values and antagonism causes negative values

^eProbability that the difference between observed and expected mortality occurred by chance based on Fisher’s exact test