Henosepilachna vigintioctopunctata susceptibility to Ttripterygium wilfordii and Datura stramonium extracts

The influence of host plants on the larvae were investigated using the dipping and biochemical methods to determine the susceptibility of Henosepilachna vigintioctopunctata larvae that feed on eggplants, potatoes, tomatoes and nightshades to Ttripterygium wilfordii and Datura stramonium extracts and the activities of the corresponding acetylcholinesterase (AChE) and detoxification enzymes. The results indicated that LC50 values of T. wilfordii extract for larvae fed on eggplants, potatoes, tomatoes and nightshades were 1.407 9 mg·L^-1, 1.595 8 mg·L^-1, 1.464 7 mg·L^-1 and 1.109 7 mg·L^-1 and the relative toxicities were 78.82, 69.54, 75.76 and 100, respectively. LC50 values of D. stramonium extract for larvae fed on eggplants, potatoes, tomatoes and nightshades were 0.641 7 mg·L^-1, 0.610 3 mg·L^-1, 0.758 0 mg·L^-1 and 0.488 3 mg·L^-1 and the relative toxicities were 76.09, 80.01, 64.42 and 100, respectively. Compared with the susceptibility of larvae fed on eggplants, potatoes and tomatoes, the susceptibility of larvae fed on nightshades to T. wilfordii and D. stramonium extracts were significantly enhanced. The activities of AChE, glutathion-S-transferase (GST), carboxyl esterase (CarE) and mixed function oxidase (MFO) were highest for larvae fed on eggplants, followed by those fed on potatoes, tomatoes and then nightshades. Compared with AChE and GST activities of larvae fed on eggplants and potatoes, AChE and GST activities of larvae fed on tomatoes and nightshades were significantly suppressed. Also compared with CarE activity of larvae fed on eggplants, CarE activities of larvae fed on potatoes, tomatoes and nightshades were significantly suppressed. There were significant differences in MFO activity of larvae fed on the four host plants. T. wilfordii and D. stramonium extracts restrained AChE and GST, CarE and MFO activities of larvae fed on eggplants, potatoes, tomatoes and nightshades. AChE activity of larvae fed on potatoes was most significantly suppressed by T. wilfordii and D. stramonium extracts, that of AChE of larvae fed on eggplants and tomatoes was obviously suppressed and yet that of AChE activity of larvae fed on nightshades was relatively suppressed. CarE activity of larvae fed on nightshades, that of MFO of larvae fed on potatoes were significantly restrained by T. wilfordii and D. stramonium extracts. The induction or restraint of detoxification enzymes by allelochemicals in host plants were the main possible reasons for the differences in pesticide susceptibilities of H. vigintioctopunctata larvae.