Abstract: 【Objective】B (Middle East-Asia Minor 1) and Q (Mediterranean) biotypes, two cryptic species of Bemisia tabaci species complex, are important agricultural pests. Extensive applications of insecticides for control of the pests have resulted in pesticide resistance in the whiteflies, have endangered ecological safety and human health. Implementation of safe pest management strategy is therefore becoming very important and urgent. Utilization of plant defense is one of the important components in integrated pest management. The objective of this study is to investigate the differential responses of nutrients and defensive enzymes in cucumber induced by the feeding of B. tabaci B and Q biotypes and thereby to elucidate the physiological and biochemical mechanism underlying defence responses of cucumber to B. tabaci.【Method】Adults of B. tabaci B and Q biotypes and cucumber plants (var. Bojie-I) from the laboratory cultures were used for the experiments. The cucumber plants at four-leaf stage were respectively used to feed 200 adults of B. tabaci B and Q biotypes, with healthy plants as controls, and the contents of nutrients (soluble sugar and soluble protein) and polyphenolic contents, activity of phenylalanine ammonialyase (PAL), the enzyme of defensive substance biosynthesis, and activity of protective enzymes in cucumber were determined after continuously feeding for 1, 3, 5, 7 and 9 days by B and Q biotypes of B. tabaci. 【Result】Within the experimental period, the contents of soluble sugar and protein in cucumber increased after 3 d by B. tabaci B biotype, but decreased after 1 d by B. tabaci Q biotype, compared to those in controls. The contents of polyphenols and activity of PAL, the key enzyme in its biosynthesis pathway, increased after infested both by B and Q biotypes, with higher activities to Q biotype feeding. The activity of superoxide dismutase (SOD) and catalase (CAT) increased and the activity of peroxidase (POD) decreased after feeding by B biotype, while the activities of SOD increased and the activity of POD and CAT decreased after feeding by Q biotype. 【Conclusion】Differential changes of nutrients and defensive enzymes in cucumber after the feeding of B. tabaci B and Q biotypes were found in the present study. Both B and Q biotypes of B. tabaci were able to induce the synthesis of defensive substance polyphenols, and increased the content of polyphenols in cucumber; but there were differences in inducing the contents of nutrients and the activities of protective enzymes, i.e., more nutrients in cucumber by B biotype feeding, while higher activities of defensive enzymes by Q biotype feeding. Those different changes in induced physiological and biochemical responses in plants to the herbivore may result from the difference in host plant adaptability between B and Q biotypes of B. tabaci. These results provide a basis for pest management strategies, especially for utilization of plant defense as the main control tactic, so as to target different biotypes of B. tabaci on different host plants.

Key words: Bemisia tabaci, B and Q biotypes, feeding induction, cucumber, nutrients, defensive substances, protective enzymes