Biological impact of harmaline,ricinine and their combined effects with <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> on <Emphasis Type="Italic">Spodoptera exigua</Emphasis> (Lepidoptera: Noctuidae) |
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| Authors: | Muhammad Rizwan-ul-Haq Qiong Bo Hu Mei Ying Hu Qing Shen Lin Wan Li Zhang |
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| Institution: | (1) Key Laboratory of Natural Pesticide and Chemical Biology, South China Agriculture University, Ministry of Education, Guangzhou, 510640, People’s Republic of China |
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| Abstract: | The history of botanical pesticides reveals that their study did mainly focus on the determination of acute median lethal
dose or concentration. In the current situation, it is the dire need to understand the sublethal effects of the botanical
extracts along with the traditional studies of lethal concentrations in order to comprehensively investigate the future role
of the botanical extracts as pesticides. This study reveals the effects of traditionally used medicinal plant extracts harmaline
(H) and ricinine (R) either individually or in combination with Bacillus thuringiensis (Bt) on the acute toxicity and sublethal effects on the nutrition and enzyme system of Spodoptera exigua. Harmaline and ricinine caused reduction in the growth of neonate larvae up to 93.12 and 84.31%. The EC50 values of harmaline against fourth and fifth instars were 0.24 and 0.27 mg/ml, but these values remained 0.49 and 0.54 mg/ml
against fourth and fifth instars after being treated with ricinine. The combination of harmaline and ricinine with Bt resulted
in the increased efficiency of these chemicals as the mortality percentages significantly increased up to 96 and 87.82% in
significantly less exposure time in case of H + Bt and R + Bt respectively, as compared to individual treatments. The nutritional
analysis revealed the increased toxicity of harmaline and ricinine in combination with Bt, but H + Bt2 showed the higher efficiency
with minimal relative consumption rate 2.50 mg/mg/day, relative growth rate 1.16 mg/mg/day and efficiency of conversion of
ingested food 29.66% of control, respectively. Changes in antioxidant enzymes such as superoxide dismutase (SOD) and catalases
(CAT) were noticed to some extent over different exposure times at all the treatments. The highest SOD (+37.29%) and CAT (+29.27%)
activity was observed at the 6th day of treatment with H + R + Bt2. The study clearly shows the significantly increased efficiency
of harmaline and ricinine in combination with Bt against S. exigua. This phenomenon can be helpful in order to develop better control strategies against different notorious pests. |
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