Microhabitat Selection In Piercing-sucking Insects And Its Ecological Mechanism

Understanding why and how piercing-sucking herbivores select oviposition microhabitats is the basis for the integrated pest management,our study explored influence of different selective factors such as predators,food and micro-environment stress and their related physical cues on foraging and oviposition micro-habitat selection in egg-laying two-spotted spider mites,Tetranychus urticae,and larvae-laying english grain aphids,Sitobion avenae.Our primary conclusions are shown as follows.(1)The influence of predator presence and density on oviposition site selection in T.urticae and S.avenae: T.urticae can detect and avoid to lay eggs on habitats with predators while cannot evaluate differences in predatory risk among habitats.In contrast,S.avenae are not able to detect presence of predators and evaluate predatory risk among habitats.(2)The influencing mechanism of leaf trichomes and leaf surfaces on oviposition microhabitat selection in T.urticae: T.urticae preferred to forage and lay eggs on pubescent leaf surfaces over glabrous leaf surfaces.Although females and their offspring could not gain direct fitness benefits from pubescent leaf surfaces,they could gain potential benefits of avoiding being preyed by predators in future.Moreover,the oviposition response to leaf trichomes is conservative regardless of food quality and predator presence.Furthermore,T.urticae population developed better on pubescent leaf surfaces even with more opredators and less quality food than glabrous leaf surfaces under variable natural environments.(3)The role of heat and UVB stress on microhabitat selection within individual leaves in T.urticae and S.avenae: both of T.urticae and S.avenae preferred to forage and lay eggs/larvae downward-facing leaf surfaces independent of abaxial or adaxial surfaces.Sunlight-avoidance was the primary reason for such within leaf distribution.Most importantly,we found that T.urticae can detect and avoid heat and UVB stress for oviposition microhabitat selection,while S.avenae can detect heat stress but are not sensitive to UVB stress during oviposition.(4)The influencing mechanism of gravity and leaf surfaces on oviposition microhabitat selection in T.urticae and S.avenae: both of T.urticae and S.avenae can use gravity as an indirect cue for laying offspring on downward-facing leaf surfaces.Although positive geotactic response during oviposition could not bring direct benefits to females or their offspring,gravity is a reliable and persistent cue indicative of potential safe sites where protect their offspring against adverse weather.T.urticae preferred to feed on abaxial rather than adaxial leaf surfaces while S.avenae preferred to feed on adaxial rather than abaxial leaf surfaces.Correspondingly,T.urticae and S.avenae females can separately maximize their fecundity on abaxial and adaxial leaf surfaces.The stomatal number is likely to be the major physical cue for leaf surface preference according to scanning electron microscope.When females face with conflicting gravity and leaf surface cues during oviposition,T.urticae primarily make oviosition decision based on gravity cue for maximizing potential offspring survival while S.avenae make oviosition decision based on leaf surface cue for maximizing female fecundity.Nevertheless,increasing direct benefits associated with favourable abaxial leaf surfaces can change T.urticae female orginal oviposition response to gravity cues.