Western corn rootworm and Bt maize

Figures & data

Table 1. Fields visited in Iowa in 2010

Mean Root Injury	Total Fields Visited	Total Populations in Bioassay
Cry3Bb1 maize
< 0.5	2	1
0.5 to 1.0	3	0
> 1.0	7	4
Cry34/35Ab1 maize
< 0.5	1	1
Pyramided maize^a
< 0.1	1	1
Total	14	7

^a Pyramided maize produces both Cry34/35Ab1 and Cry3Bb1.

Figure 1. Distribution of (A) fields sampled in Iowa for use in bioassays and (B) control sites within the United States. For (B), Iowa is highlighted in gray.

Table 2. Detailed field history for populations used in bioassays in 2010^ab

Year
Site	2003	2004	2005	2006	2007	2008	2009	2010
S1	4 or 5 (?)	4	4	4	1	1	1	1 & 3
S2	1 or 4 (?)	1 or 4 (?)	1 or 4 (?)	1 & 2	1 & 2	1 & 2	2	2
S3	4	1	1	1	1	1	1	1 & 3
S4	unknown	unknown	unknown	unknown	1	1	1	1
S5	4	4	1	1	4	4	1	1
S6	4	1	1	1	1	1	1	1 & 3
S7	unknown	unknown	unknown	5 (?)	1	1	1	1

^a Field history indicates the crop planted in a field each year. 1 = Cry3Bb1 maize, 2 = Cry34/35Ab1 maize, 3 = maize producing both Cry3Bb1 and Cry34/35Ab1, 4 = maize lacking rootworm active Bt, 5 = soybean. A field was only coded as “4 non-Bt maize” or “5 soybean” if the entire field was planted to non-Bt maize or soybean, respectively. ^bunknown = no data are available for the type of crop planted; (?) with “or” means there was uncertainty about which of two crops was planted; (?) alone means there was uncertainty about whether or not a specific crop was planted.

Table 3. Date sampled, root injury, corrected survival and field history for 2010 populations

Site	Date Sampled	Maize Type^a	Root Injury^b	Corrected Survival^b		Field History^c,d
				Cry3Bb1	Cry34/35Ab1	1	2	3	4	5
S1^e	03 Aug	1	1.21 ± 0.60	0.96 ± 0.11	0.13 ± 0.09	4	0	1	3–4	0–1
S2^e	10 Aug	2	0.45 ± 0.06	0.89 ± 0.14	0.00 ± NA	3–6	5	0	0–3	0
S3	03 Aug	3	0.02 ± 0.01	0.83 ± 0.11	0.12 ± 0.06	7	0	1	1	0
S4^f	03 Aug	1	0.48 ± 0.21	0.79 ± 0.10	0.08 ± 0.03	4	0	0	0	0
S5	03 Aug	1	1.10 ± 0.26	0.65 ± 0.12	0.12 ± 0.05	4	0	0	4	0
S6	10 Aug	1	2.57 ± 0.09	0.60 ± 0.13	0.00 ± NA	7	0	1	1	0
S7^e,g	03 Aug	1	1.22 ± 0.23	0.51 ± 0.12	0.04 ± 0.03	4	0	0	0	0-1
Mean ± SE				0.74 ± 0.06	0.07 ± 0.02

^a Type of maize evaluated for root injury. 1 = Cry3Bb1 maize, 2 = Cry34/35Ab1 maize, 3 = maize producing both Cry3Bb1 and Cry34/35Ab1. ^bMean ± Standard Error. ^cField history indicates the number of field years a certain crop was planted. In some years more than one type of Bt maize was planted and both types were scored as being in the field for one year. 1 = Cry3Bb1 maize, 2 = Cry34/35Ab1 maize, 3 = maize producing both Cry3Bb1 and Cry34/35Ab1, 4 = maize lacking rootworm active Bt, 5 = soybean. ^dA field was only coded as “4 non-Bt maize” or “5 soybean” if the entire field was planted to non-Bt maize or soybean, respectively. ^eThere was some uncertainty regarding field history and this is reflected in the range of values. ^fField history was only available from 2007 to 2010. ^gField history was only available from 2006 to 2010.

Figure 2. Survival of western corn rootworm on (A) Cry3Bb1 maize and (B) Cry34/35Ab1 maize. Bar heights represent sample means and error bars are the standard error of the mean. Letters indicate pairwise differences among means.

Table 4. Location, corrected survival and date taken into culture for control populations

Site	Location	Year in Culture	Corrected Survival^a
			Cry3Bb1	Cry34/35Ab1
C1	Butler Co., Nebraska	1999	0.08 ± 0.04	0.13 ± 0.07
C2	Potter Co., South Dakota	1995	0.07 ± 0.05	0.11 ± 0.05
C3	York Co., Nebraska	1999	0.07 ± 0.05	0.14 ± 0.04
C4	Centre Co., Pennsylvania	2001	0.05 ± 0.02	0.06 ± 0.03
C5	Finney Co., Kansas	2000	0.05 ± 0.03	0.00 ± NA
C6	Phelps Co., Nebraska	1995	0.00 ± NA	0.04 ± 0.02
Mean			0.05 ± 0.01	0.08 ± 0.02

^a Mean ± Standard Error.

Figure 3. Correlation analysis for survival of populations on Cry3Bb1 maize and Cry34/35Ab1 maize. Symbols correspond to Tables 3 and 4.

Table 5. Proportion of insects in each larval instar by population type and maize hybrid

Instar	Significant Factors^a			Population Type and Maize Hybrid^b,c
				2010 Populations		Control Populations
				Cry3Bb1	Non-Bt^d	Cry3Bb1	Non-Bt^d
First	H	P	I	0.02 ± 0.01^A	0.00 ± 0.00^A	0.16 ± 0.07^B	0.02 ± 0.01^A
Second	H	-	-	0.40 ± 0.06^A	0.26 ± 0.09^B	0.52 ± 0.16^A	0.17 ± 0.06^B
Third	H	-	I	0.58 ± 0.06^AB	0.74 ± 0.09^A	0.32 ± 0.12^B	0.81 ± 0.07^A
				2010 Populations		Control Populations
				Cry34/35Ab1	Non-Bt^d	Cry34/35Ab1	Non-Bt^d
First	H	-	-	0.12 ± 0.07^A	0.01 ± 0.00^B	0.26 ± 0.14^A	0.01 ± 0.01^B
Second	H	-	-	0.76 ± 0.12^A	0.38 ± 0.08^B	0.59 ± 0.18^A	0.23 ± 0.06^B
Third	H	-	-	0.12 ± 0.05^A	0.61 ± 0.08^B	0.15 ± 0.08^A	0.76 ± 0.07^B

^a Effects in the ANOVA that were significant. H = maize hybrid (Bt vs. non-Bt), P = population type (2010 population vs. control population), I = the interaction between maize hybrid and population type. ^bCapital letters indicate significant differences among means within a row, which were based on significant main factors (H or P) in the ANOVA or on pairwise comparisons in cases where a significant interaction (I) was present. ^cMean ± Standard Error. ^dRepresents non-Bt near isoline of the companion Bt hybrid.