Modulation of BT Cry Toxin Expression by Nitrogen and its Residual Presence in Non-Target Insects

A study was conducted to evaluate the effect of nitrogen fertilizer levels on the expression of CrylAc and Cry2Ab proteins in Bt cotton cultivars and their translocation into sucking pests and honeydew. Six cultivars (Ankur 3028, Bioseed 6588, NCS 855, RCH 650, RCH 773, and RCH 776) were tested under four nitrogen levels (0, 65, 100, and 130 kg/ ha) at 60 and 120 days after sowing (DAS). ELISA analysis revealed that Cry protein expression significantly increased with higher nitrogen application and declined as the plants aged. At 60 DAS, CrylAc content ranged from 2.15 to 4.37 μg/ g fresh weight, with the highest expression in RCH 776 at 130 kg N/ ha. Similarly, Cry2Ab content ranged from 18.78 to 23.33 μg/ g, with RCH 773 and RCH 776 recording the highest values. At 120 DAS, Cry1Ac and Cry2Ab levels declined, ranging from 1.37 to 2.18 μg/ g and 17.37 to 20.32 μg/ g, respectively. Among the cultivars, RCH 776 consistently showed higher Cry protein expression at both stages and nitrogen levels. Trace amounts of Cry1Ac (0.033-0.094 μg/ g) and Cry2Ab (0.931-1.084 μg/ g) were detected in jassid nymphs and whitefly adults, while honeydew samples from all treatments showed negligible levels (<0.009 μg/ g). These findings confirm that nitrogen significantly enhances Bt toxin expression in cotton leaves, particularly at early growth stages, and suggest minimal translocation of the toxin into phloem-feeding insect pests and their excreta.