| This research was conducted to compare growth, development, physiology, biochemistry and behavioral responses of two polyphagous phloem-feeding herbivores(Bemisia tabaci Biotype B and Bactericera cockerelli) in polyculture treatments with those in monoculture treatments. Activities of enzymes in host plants related to secondary metabolites and plant defense were also measured to analyze the response of plants.Effects of a mixture of tomato, cabbage, cotton, cucumber, kidney bean, and a mixture of tomato, Chinese cabbage, summer squash, kidney bean, and a mixture of canola, cotton, tomato, cucumber on Bemisia tabaci were measured. Effects of a mixture of potato, tomato, eggplant, and a mixture of pepper, tomato, eggplant on Bactericera cockerelli were measured. Polyculture was a mixture of different plant species(choice experiments), while monoculture contained only one plant species(non-choice experiments). 1. Effects of host diversity on ecological index of B. tabaci and Bactericera cockerelliB. tabaci female adults fed on a mixture of tomato, cabbage, cotton, cucumber and kidney bean in polyculture survived longer and laid more eggs than those fed in monoculture. This mixture benefited whiteflies. B. tabaci fed on a mixture of tomato, Chinese cabbage, summer squash and kidney bean survived longer and laid more eggs than two monoculture treatments, while lived shorter and produced less eggs than the other two monoculture treatments. Impact of this mixture is in the middle level. Ninth-day survival rate and NO. eggs of whiteflies in the canola-cotton-tomato-cucumber polyculture significantly decreased when compared with those in monoculture. This mixture did not benefit whiteflies.Bactericera cockerelli fed on the polyculture of potato, tomato and eggplant survived longer and laid more eggs than those fed in monoculture. This mixture benefited psyllids. However, the polyculture of pepper, tomato and eggplant did not contribute to Bactericera cockerelli. Survival rate and NO. eggs of psyllids in polyculture significantly decreased.Among these five experiments, host plant diversity had no significantly effect on development and survival of immature of B. tabaci and Bactericera cockerelli. Average NO. eggs of B. tabaci and Bactericera cockerelli on different plants in choice treatments had significantly positive correlation with those on the same plant species in non-choice treatments, respectively. This meant B. tabaci showed the same oviposition preference in polyculture and monoculture, so was Bactericera cockerelli.When choice treatments had low-ranking host plants, development of whiteflies and psyllids appeared to be affected, this adverse impact might have positive correlation with the number of low-ranking plants. Conversely, when high-ranking hosts existed, whiteflies and psyllids showed preference to them. However, the results were also affected by quality of low-ranking host plants or combined impact. 2. Effects of host diversity on nutrition and enzymes in B. tabaci and Bactericera cockerelliActivities of superoxide dismutases(SOD) and alkaline phosphatase(AKP) in B. tabaci fed in the polyculture of tomato, cabbage, cotton, cucumber and kidney bean were lower than those fed in monoculture, whereas activities of sucrase and amylase in B. tabaci in polyculture were higher than those from monoculture. Activities of SOD, AKP in B. tabaci fed in the polyculture of tomato, Chinese cabbage, summer squash, and kidney bean were higher than those fed in monoculture, while concentrations of total protein and trehalose were not significantly different. Activities of SOD, AKP, and trehalose in B. tabaci in the canola-cotton-tomato-cucumber polyculture increased. Activities of detoxification enzymes in Bactericera cockerelli in the polyculture of potato, tomato, and eggplant decreased while nutrition enzymes, total protein and trehalose increased. Conversely, detoxification enzymes in Bactericera cockerelli in the polyculture of pepper, tomato, and eggplant increased while nutrition enzymes and total protein decreased significantly.Activities of detoxification enzymes in both B. tabaci and Bactericera cockerelli had general negative correlation with oviposition, survival and nutrition enzymes. Activities of nutrition enzymes had general positive correlation with oviposition and survival. Trehalose had positive correlation with trehalase. In beneficial combinations, activities of detoxification enzymes decreased and nutrition enzymes increased. Whereas, in disadvantageous combinations, detoxification enzymes increased and nutrition enzymes decreased. 3. Effects of host diversity on behavioral responses of B. tabaci and Bactericera cockerelliB. tabaci female adults showed relatively stronger preference to a mixture of tomato, cabbage, cotton, cucumber and kidney bean. While they showed stronger selective reaction to monoculture in tomato-Chinese cabbage-summer squash-kidney bean combination and canola-cotton-tomato-cucumber combination. Bactericera cockerelli showed stronger selective reaction to the polyculture of potato, tomato, eggplant than monoculture. In pepper-tomato-eggplant experiment, Bactericera cockerelli showed avoidance response to the existence of pepper. 4. Defense reaction of plants to feeding of B. tabaci and Bactericera cockerelliSelective damage of whiteflies and psyllids contributed to different increases of activities of SOD, polyphenol oxidase(PPO), peroxidase(POD) and catalase(CAT) in host plants. In tomato-cabbage-cotton-cucumber-kidney bean experiment, SOD levels in whiteflies were positively correlated with POD in plants. There was a positive correlation between survival of whiteflies and increase of PPO, POD in plants, and also between sucrase in whiteflies and PPO, POD in plants. In tomato-Chinese cabbage-summer squash-kidney bean combination, sucrase in whiteflies had positive correlation with CAT in plants. There was a positive correlation between survival of psyllids and increase of PPO in plants, and a negative correlation between trehalose in psyllids and SOD in plants in pepper-tomato-eggplant experiment.In conclusion, this study illustrated effects of host diversity on B. tabaci and Bactericera cockerelli, and these two polyphagous insects showed similar mechanisms in orientation, feeding, oviposition, detoxication and access to nutrition. In practice, monoculture and intensively farmed crops easily lead to simple ecological environment, resulting in a large outbreak of pests. This research explained some mechanisms in plant-polyphagous insect interaction, and potentially provided simple and efficient ways for the control of polyphagous insects, theoretically and practically. In order to achieve sustainable development, we should pay full attention to the modulation function of biodiversity and crop diversification, and add good structure and funtion to agroecosystem. |
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