| Kairomone cues released from hosts or prey are of crucial importance to natural enemies for pest habitat location and pest location.Predatory natural enemies can use herbivorous insect sex pheromone to locate and prey on them.Harmonia axyridis is the dominate predator of Spodotera frugiperda.We hypothesized that H.axyridis could perceive and use the sex pheromone of S.frugiperda to locate its habitat so as to improve the success of predation.Here we tested the electrophysiological and behavioral responses of H.axyridis to the two components Z7-12:Ac and Z9-14:Ac of S.frugiperda sex pheromone by using electroantennography(EAG)and Y-tube bioassay.The 3D modeling of H.axyridis odorant-binding proteins Haxy OBPs and molecular docking were also performed.The main results are as follows:1.Both female and male H.axyridis exhibited significantly higher electrophysiological responses to Z9-14:Ac at the concentrations of 0.001,0.01 and 0.1 μg/μL,while no significant responses of H.axyridis were observed to Z7-12:Ac.The blend of Z7-12:Ac and Z9-14:Ac at the ratio of 1:100 had a significant attraction to both male and female H.axyridis at the concentrations of 0.0001,0.001,0.01 and 0.1 μg/μL,but no significant EAG responses were observed at the ratios of 1:9.2.The Y tube bioassay showed that male and female H.axyridis were strongly attracted to Z9-14:Ac at 0.001,0.01,0.1 μg/μL,but had no significant response to Z7-12:Ac.The blend of Z7-12:Ac and Z9-14:Ac at the ratio of 1:100 showed strong attraction to H.axyridis at 0.01 and 0.1 μg/μL,while 1:9 did not.3.According to the 3D modeling of Haxy OBPs and molecular docking,Haxy OBP12 had a higher affinity with Z9-14:Ac,which was bonded by hydrogen bonding and hydrophobic interactions.However,there were no credible docking results between Haxy OBPs and Z7-12:Ac.Our findings revealed that H.axyridis can perceive Z9-14:Ac and could use it as a chemical cue to locate prey habitat.We speculated that Z7-12:Ac,which showed some antagonistic effect towards H.axyridis,could improve the adaptability of S.frugiperda to the predators under natural enviroment.In this study,sex pheromones from S.frugiperda were used to determine the pheromone preference and the perceptive mechanism of predatory ladybeetle,which provided new insights into the application of pheromones in insect pest control. |
