author(s)
Shah Vivek, Chitra Srivastava, S Subramanian and Naveen NC

abstract
Neonicotinoid is the major class of insecticides used for management of sucking pests in cotton. The present investigation was done to know the susceptibility level of Bemisia tabaci to neonicotinoids and its association with detoxifying enzyme, cytochrome P450. In the present study five populations of B. tabaci were collected representing two regions/zones of country viz., North (Delhi, Punjab and Rajasthan) and Central (Madhya Pradesh and Maharashtra) with one location from each state. The locations were New Delhi, Sriganganagar (RJ), Ludhiana (PJ), Khandwa (MP), and Amravati (MH). The populations were collected and bioassayed with neonicotinoids two consecutive years (2013-14 and 2014-15) and their cytochrome P450 levels were quantified. The populations from Sriganganagar, Ludhiana and Amravati showed highly reduced susceptibility with LC₅₀ values ranging from 1199 to 1874 mg/lit during 2013-14 and 1315 to 1717 mg/lit during 2014-15 for all three neonicotinoids tested whereas, Khandwa showed moderate level of tolerance with LC₅₀ values 717 to 1012 mg/lit and 854 to 973 mg/lit during first and second year of evaluation respectively. New Delhi populations showed low level of tolerance with LC₅₀ values below 400 mg/lit and 500 mg/lit during first and second year of evaluation respectively. A strong correlation between bioassay results and cytochrome P450 level was observed. The populations were compared with laboratory susceptible strain collected from wild host, Leucaena leucocephala. All the five populations belong to Asia II 1 genetic group whereas lab susceptible strain belongs to Asia II 7 genetic group. Cytochrome P450 is the key enzyme involved in neonicotinoid detoxification and using synergists that inhibit the P450 activity and field efficacy of this group may be enhanced.