| The impacts of infestation by the green peach aphid (Myzus persicae) on sweetpotatowhitefly (Bemisia tabaci) settling on tomato were determined in the orthogonal design testthrough manipulations of four factors: durations of aphid infestation, density of aphids,intervals between aphid removal after different durations of infestation and the time ofwhitefly release, and leaf positions on the plants. The most important factor in the four factorsthat affected the induced plant defense against whiteflies had been determined. The highestand lowest whitefly response treatments were also determined.1. The results of direct and indirect effect tests to whiteflies demonstrated that B. tabacipreferred to settle on the plant leaves that had not been infested by aphids when they had achoice. The whiteflies were able to settle on the plant on which aphids had previously infested,and also could settle on leaves with aphids if no uninfested plants were available. Tests ofdirect factors revealed that duration of aphid infestation had a stronger effect on whiteflylanding preference than aphid density; whitefly preference was the least when20aphids fedon the leaves for72h. Tests of indirect effects revealed that the major factor that affectedwhitefly preference for a host plant was the interval between the time of aphid removal afterinfestation and the time of whitefly release. The importance of the four factors that affectedthe induced plant defense against whiteflies can be arranged in the following order: timeintervals between aphid removal and whitefly release> durations of aphid infestation>density of aphids> leaf positions on the plants. In conclusion, the density of aphid infestationand time for which they were feeding influenced the production of induced compounds bytomatoes, the whitefly responses to the plants, and reduced interspecific competition.2. The activities of nutrients and defense proteins in tomato leaves of the highest andlowest responses of B. tabaci in the direct and indirect treatments from orthogonal design testwere determined. The contents of soluble sugar, PPO, POD, SOD, PAL, β-1,3glucanase,total phenol and chitinase were significant impacted by the different aphid feeding and these metabolic substances were increased significantly in some systemic leaves on which aphidsdid not infest. But the contents of total protein and PI were not significant differencecompared with the tomato leaves without aphid feeding. The contents of PPO, POD, and PALwere significantly increased as compared with those on the leaves without aphid feeding inseveral treatments. The content of SOD was higher than the control in some treatments, butsome are lower than in the control. However, the content of β-1,3glucanase was significantlyincreased in all treatments and in all systemic leaves. The contents of soluble sugar, PPO,POD, SOD, and PAL in the lower leaves were higher than in the middle leaves with aphidfeeding in indirect effect test. But the content of total phenol is different, and the upper leaveshad the highest contents. The content of β-1,3glucanase was higher in the middle of aphidsfed leaves than the upper and lower leaves. However, all of the upper and lower leaves werehigher than its corresponding control, and the results also proved that the activities of β-1,3glucanase increased in the systemic leaves. The contents in the leaves of indirect effect testwere higher than those in the direct effect test. Chitinase also increased in the systemic leaves,but there were no difference among the three leaves.3. The influences of M. persicae-induced tomato plant volatile compounds on theolfactory responses of B. tabaci, three species of predators (Coccinella septempunctata,Propylea japonica and Orius sauteri), two species of whitefly parasitoids (Encarsia formosaand E. sophia), and one species of aphid parasitoid (Aphidius gufiensis) were examined intwo-choice tests using a4-arm olfactometer. Tomato plants were experimentally altered foraphid density, duration of feeding, and duration between aphid removal and whitefly release.We also compared the systemic effects of aphid feeding on whiteflies according to threerelative leaf positions; the aphid-infested leaf itself, and two adjacent leaves (above andbelow). B. tabaci were deterred by the odours of the leaves infested with aphids in alltreatments. All six natural enemies were attracted to the odours of the leaves infested withaphids. B. tabaci deterrence was greater for volatiles from leaves at the highest aphid density,and with increasing duration of exposure to aphid feeding. In contrast, the attraction tovolatiles from leaves was greater for the three parasitoids than for the three predators bothwith increasing aphid density and increasing duration of exposure to aphids. There was nosignificant influence of leaf position on preference for B. tabaci, the two species of ladybeetles and the aphid parasitoid. The two Encarsia species were attracted to volatiles from theleaf above the aphid-infested leaves, indicating that systemic volatile-base defenses occurredin adjacent leaves. However, O. sauteri was only attracted by volatiles from the aphid-infested leaf itself. Our results showed that M. persicae-infested host plants emitted volatiles thatcould inhibit the colonization of B. tabaci and also attract natural enemies of both aphids andwhiteflies. The responses varied between the species of predators and parasitoids, whichwould need to be considered in relevant community ecology studies and for pest management.4. We quantified Page:13Tomato yellow leaf curl virus (TYLCV) DNA in leaves, stems and roots of tomato plants andin B. tabaci using gene specific primers and TaqMan probes for the first time. We conductedan experiment to determine the effects of tomato plants infested by M. persicae ontransmission and acquisition of TYLCV by B. tabaci. The experiment investigated thefollowing factors: infestation duration of aphid, position of tomato plant and feeding durationof whitefly. The TYLCV DNA concentration in tomato plants transmitted by whitefly wassignificantly affected by the duration of aphid infestation and by the different plant parts.TYLCV in tomato roots, stem, and leaves increased initially, and then decreased with overtime of aphid infestation. Systemic response was detected and can be significantly affected byduration of aphid infestation. The duration of aphid infestation and whitefly exposure hadsignificant effects on TYLCV DNA concentration in whitefly fed on TYLCV-infected tomatoplants, and decreased with over time of whitefly feeding. In conclusion, aphid-infested tomatoplants could increase transmission of TYLCV by viruliferous whiteflies feeding on tomatoplant, and also inhibited the acquisition of TYLCV by whiteflies feeding on theTYLCV-infected tomato plants. These data suggest that there may be an opposite effect frominfestation of the first arriving herbivorous insects on the transmission and acquisition ofpathogens by the secondarily arriving insects. |
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