Cry1Ac and Cry2Ab Toxin Expression across different Tiers in aphid feeding
The study delved into the expression patterns of Cry1Ac and Cry2Ab toxins in various tiers of the ecosystem surrounding BG II cotton plants. The maximum amounts of Cry1Ac and Cry2Ab proteins were present in the leaves of BG II cotton, followed by A. gossypii and C. z. sillemi (Figs. 1 & 2). Significant differences in Cry1Ac (F = 303.8; df = 2; p < 0.001) and Cry2Ab (F = 4.4; df = 2; p < 0.001) toxins were observed in leaves among different day-old Bt cotton plants. During the treatment days, the maximum concentration of Cry1Ac and Cry2Ab protein was detected at 60 DAS (7.36 µg/g FW and 23.54 µg/g FW) and the minimum at 40 DAS (2.36 µg/g FW and 7.78 µg/g FW). However, in Bt cotton-fed A. gossypii, no significant differences were observed among the three Bt treatments of Cry1Ac (F = 1.82; df = 2; p = 0.67) and Cry2Ab (F = 0.52; df = 2; p = 0.88). The concentrations of Cry1Ac and Cry2Ab toxins ranged from 0.17–0.24 and 0.35–0.41 µg/g FW in Bt-reared aphids. Similarly, differences were also non-significant for Cry1Ac (F = 0.81; df = 2; p = 0.46 and F = 0.67; df = 2; p = 0.53) and Cry2Ab (F = 0.96; df = 2; p = 0.41 and F = 1.3; df = 2; p = 0.60) toxins in the larvae and Chrysoperla adults reared with Bt cotton prey. In C. z. sillemi larvae, the Cry1Ac and Cry2Ab toxins ranged from 0.12–0.16 and 0.17–0.26 µg/g FW, respectively. In C. z. sillemi adults, the Cry1Ac concentration and Cry2Ab concentration varied from 0.04 to 0.07 µg/g FW from 0.07 to 0.09 µg/g FW, respectively. In all three tiers, non-Bt leaves, non-Bt reared prey, and predators did not show the presence of any Bt toxin.
Cry1Ac and Cry2Ab Toxin Expression across different Tiers in whitefly feeding
The analysis of leaves showed Cry1Ac toxin concentrations in the range of 1.89 to 6.09 and Cry2Ab concentrations in the range of 6.13 to 19.89 µg/g FW (Figs. 3 & 4). The maximum concentration of both Cry1Ac and Cry2Ab proteins (6.09 and 19.89) in leaves was present at 70 DAS and was significantly higher (F = 600.6; df = 2; p < 0.001 and F = 93.3; df = 2; p < 0.001) than the Cry protein concentrations detected in 90 and 110 day old Bt cotton plants. However, there were no significant differences (F = 0.61; df = 2; p = 0.0.56; and F = 1.7; df = 2; p = 0.22) between the levels of Cry toxins (both Cry1Ac and Cry2Ab) in the Bt-reared B. tabaci among all three Bt treatments. The Cry1Ac and Cry2Ab concentrations in Bt cotton-reared B. tabaci ranged from 0.21 to 0.29 µg/g FW and 0.32 to 0.43 µg/g FW, respectively. A small amount of Bt toxins was detected at the third trophic level of predators in Chrysoperla larvae (F = 0.71; df = 2; p = 0.52 and F = 1.9; df = 2; p = 0.78) and adults (F = 0.05; df = 2; p = 0.95 and F = 2.01; df = 2; p = 0.17). However, no Cry proteins were found in the non-Bt plants, non-Bt-fed prey, and predator-fed on non-Bt reared prey.
Development of C. z. sillemi fed Bt and non-Bt reared A. gossypii
Different developmental parameters such as the total larval development period (Cultivars, F = 2.89; df = 1; P = 0.10; Days, F = 4.17; df = 2; P = 0.11; interaction, F = 0.24; df = 2; P = 0.90) and pupal period (Cultivars, F = 4.43; df = 1; P = 0.06; days, F = 1.86; df = 2; P = 0.17; interaction, F = 0.23; df = 2; P = 0.79), of C. z. sillemi did not indicate any statistically significant difference between the two treatments, including the interaction factor among the days and cultivars (Figs. 5 & 6). There were also insignificant differences in larval survival (t = 1.49; df = 28; P = 1.42) and adult emergence (t = 1.19; df = 28; P = 0.84) between treatments (Table 1). Likewise, for C. z. sillemi adults, fresh weight of males (Cultivars, F = 0.22; df = 1; P = 0.64; days, F = 0.46; df = 2; P = 0.63; interaction, F = 0.03; df = 2; P = 0.96) and females (Cultivars, F = 0.85; df = 1; P = 0.36; days, F = 0.33; df = 2; P = 0.72; interaction, F = 0.01; df = 2; P = 0.98), male longevity (Cultivars, F = 0.82; df = 1; P = 0.37; days, F = 0.46; df = 2; P = 0.64; interaction, F = 0.01; df = 2; P = 0.98) and female longevity (Cultivars, F = 0.68; df = 1; P = 0.42; days, F = 0.53; df = 2; P = 0.59; interaction, F = 0.01; df = 2; P = 0.98) were also statistically at par for both the Bt and non-Bt treatments at different days as well as the interaction of three different treatment days and cultivars of bioassay (Figs. 7 & 8; Figs. 9 &10).
Table 1
Larval survival and adult emergence of C. z. sillemi fed with A. gossypii reared on Bt and non Bt cotton cultivars
Parameters
|
Cultivars
|
Days after sowing (DAS)
|
Statistical analysis
|
40 DAS
|
60 DAS
|
80 DAS
|
Larval survival#(%±SE)
|
Bt
|
93.4 ± 0.45
|
91.0 ± 0.28
|
92.4 ± 0.44
|
t = 1.49; df = 28; P = 1.42
|
Non-Bt
|
94.4 ± 0.10
|
91.6 ± 0.16
|
93.2 ± 0.12
|
Adult emergence#(%±SE)
|
Bt
|
92.8 ± 1.34
|
90.2 ± 1.59
|
91.4 ± 1.02
|
t = 1.19; df = 28; P = 0.84
|
Non-Bt
|
93.9 ± 1.18
|
91.6 ± 1.18
|
92.4 ± 1.39
|
Mean (± SE) of five replications,10 individuals per replication with 50 larvae per treatment; t-test (p<0.05)
Development of C. z. sillemi fed Bt and non-Bt reared B. tabaci
The results of the feeding bioassay studies revealed no significant differences between the total larval development period (Cultivars, F=179; df = 1; P= 0.19; days, F=6.15; df= 2; P=0.10; interaction, F= 0.12; df = 2; P=0.99) and pupal period (Cultivars, F=3.21; df = 1; P= 0.09; days, F=1.39; df = 2; P=0.27; interaction, F= 0.14; df = 2; P=0.87) of C. z. sillemi fed with B. tabaci reared on Bt and non-Bt cotton plants on different treatment days (Figures 11 &12). Similarly, the larval survival (t= 1.18; df= 28; P=0.56) and percentage of adult emergence (t=0.54, df= 28; P=0.73) also did not show any significant difference between the Bt and non-Bt treatments (Table 2). Additionally, differences were insignificant for the fresh weight of newly emerged adult females (Cultivars, F=0.25; df = 1; P= 0.62; days, F=0.19; df = 2; P=0.83; interaction, F= 0.01; df = 2; P=0.99) and males (Cultivars, F=0.35; df = 1; P= 0.56; days, F=0.27; df = 2; P=0.76; interaction, F= 0.02; df = 2; P=0.98) and male longevity (Cultivars, F=0.32; df = 1; P= 0.57; days, F=0.48; df = 2; P=0.63; interaction, F= 0.00; df = 2; P=0.99) and female longevity (Cultivars, F=1.45; df = 1; P= 0.24; days, F=3.37; df = 2; P=0.04; interaction, F= 0.04; df = 2; P=0.95) between the Bt and non-Bt cotton. The interaction factor was also insignificant for various biological parameters for days and cultivars (Figures 13 & 14; Figures 15 & 16).
Table 2 Larval survival and adult emergence of C. z. sillemi fed with B. tabaci reared on Bt and non Bt cotton cultivars
Parameters
|
Cultivars
|
Days after sowing (DAS)
|
Statistical analysis
|
70 DAS
|
90 DAS
|
110 DAS
|
Larval survival#(%±SE)
|
Bt
|
89.2±0.32
|
91.0±0.24
|
91.9±0.22
|
t= 1.18; df=28; P=0.56
|
Non-Bt
|
90.4±0.10
|
91.6±0.21
|
92.2±0.29
|
Adult emergence#(%±SE)
|
Bt
|
91.8±1.13
|
90.2±1.37
|
91.4±1.09
|
t=0.54, df=28; P=0.73
|
Non-Bt
|
93.9±1.18
|
91.6±1.09
|
92.4±1.39
|
Mean (± SE) of five replications,10 individuals per replication with 50 larvae per treatment; t-test (p<0.05)