Table 1.

Estimated frequency of alleles conferring resistance to Bt crops in field populations of lepidopteran pests targeted by Bt corn or Bt cotton. Note that in most studies, frequency estimates were obtained after introduction of a Bt crop, which could have increased estimates of the resistance allele frequency. Insects were screened for resistance on Bt leaves or Bt crop plants unless noted otherwise

Location	Crop	Toxin	1st year*	Years sampled†	Frequency	Confidence limits‡	Reference
Gelechiidae
Pectinophora gossypiella
AZ	Cotton	Cry1Ac	1996	1997	0.16§	0.05–0.26	Tabashnik et al. (2005a)
	Cotton	Cry1Ac	1996	1998	0.007§	0–0.02	Tabashnik et al. (2005a)
	Cotton	Cry1Ac	1996	2004	0.004§	0–0.01	Tabashnik et al. (2005a)
AZ, CA, TX	Cotton	Cry1Ac	1996	2001–05	0¶	0–0.0003	Tabashnik et al. (2006)
Noctuidae
Helicoverpa armigera
Australia	Cotton	Cry1Ac	1996	2002–06	0**	0–0.0009	Mahon et al. (2007)
Australia	Cotton	Cry2Ab	2004/05	2002–06	0.0033§	0.0017–0.0055	Mahon et al. (2007)
China	Cotton	Cry1Ac	1998	2006–07	0.094	0.044–0.145	Liu et al. (2008)
China	Cotton	Cry1Ac	1998	2003–05	0.0146	0.0084–0.0225	Xu et al. (2009)
Heliothis virescens
LA, MS, NC, TX	Cotton	Cry1Ac	1996	1993	0.0015††	0.0003–0.0041	Gould et al. (1997)
LA, TX	Cotton	Cry1Ac	1996	1996–2002	0¶	0–0.0021	Gahan et al. (2007)
Sesamia nonagrioides
Spain	Corn	Cry1Ab	1998	2004–05	0	0–0.0086	Andreadis et al. (2007)
Greece	Corn	Cry1Ab	–‡‡	2004–05	0	0–0.0097	Andreadis et al. (2007)
Pyralidae
Diatraea grandiosella
LA	Corn	Cry1Ab	1996	2005	0	0–0.0035	Huang et al. (2007a)
Diatraea saccharalis
LA	Corn	Cry1Ab	1996	2004	0.0023	0.0003–0.0064	Huang et al. (2007b)
LA	Corn	Cry1Ab	1996	2005	0	0–0.0027	Huang et al. (2008a)
TX	Corn	Cry1Ab	1996	2007	0	0–0.0016	Huang et al. (2009)
Ostrinia nubilalis
KS, TX	Corn	Cry1Ab	1996	2000–01	0	0–0.0044	Stodola et al. (2006)
France	Corn	Cry1Ab	–‡‡	1999–2000	0	0–0.00092	Bourguet et al. (2003)
MN, SD, IA	Corn	Cry1Ab	1996	1997–2000	0	0–0.00042	Bourguet et al. (2003)
KS, TX	Corn	Cry1Ab	1996	2000–01	0	0–0.0077	Bourguet et al. (2003)

^*First year Bt crop was grown commercially in the location monitored.

^†Year (s) insects were sampled to produce the frequency estimate.

^‡The probability is 95% that the true mean is between the upper and lower limits.

^§Insects were screened on diet with high Bt toxin concentration and related work showed that insects surviving this concentration also survive on Bt cotton.

^¶Insects were screened for cadherin mutations associated with survival on Bt cotton (P. gossypiella) or high resistance to Cry1Ac in diet (H. virescens).

^**Insects were tested on diet with Cry1Ac but not on Bt cotton.

^††Insects were not tested on Bt cotton but resistance to Cry1Ac in diet was very high.

^‡‡Bt corn was not commercialized in region sampled.