The Roles Of Thrips Aggregation Pheromones In Interspecific Interactions

Aggregation pheromone is one important chemical signal for the behavior regulation of insects,which plays important roles in not only intraspecific interactions but also interspecific interactions.Western flower thrips,Frankliniella occidentalis,flower thrips,Frankliniella intonsa and Melon thrips,Thrips palmi are important horticultural and agricultural pests,causing serious damage to host plants by direct feeding and indirect transmission of the plant virus.The similar niches of these thrips species lead to the intensive inter-specific competitions between them.It has been reported that the major compounds or ratio of aggregation pheromones of these thrips species are different.The aggregation pheromones of F.occidentalis and F.intonsa,have been identified with the same major compounds,(R)-lavandulyl acetate and neryl(S)-2-methylbutanoate,but in different ratios.The aggregation pheromone of T.palmi have been identified as a compound(R)-lavandulyl 3-methyl-3-butenoate.It is still unclear that if the aggregation pheromones play important roles between the interspecific competition of these thrips species.In this study,we firstly determined the optimal blends of aggregation pheromones for trapping F.occidentalis,F.intonsa and T.palmi adults in fields by field trapping experiments.Then,we investigated the roles of major aggregation pheromone compounds in interspecific interactions among F.occidentalis,F.intonsa and T.palmi by Y-tube olfactometer bioassays,field trapping experiments and cage experiments.The main results are as follows:1.The optimal blends of aggregation pheromone components for trapping F.occidentalis,F.intonsa and T.palmi adults in fields:the results showed that the optimal blend for trapping F.occidentalis female adults was 1250 ng(R)-lavandulyl acetate and 10000 ng neryl(S)-2-methylbutanoate,while that for trapping F.intonsa female adults was 1250 ng(R)-lavandulyl acetate and 5000 ng neryl(S)-2-methylbutanoate;for T.palmi adults,the optimal trapping dose of(R)-lavandulyl 3-methyl-3-butenoate was 40000 ng.2.The interspecific interaction between F.occidentalis and F.intonsa:the Y-tube olfactometer bioassays showed that the aggregation pheromones of F.occidentalis had no significant attraction to both male and female adults of F.intonsa and vice versa.The field trapping experiments showed that the synthetic aggregation pheromone blend of F.occidentalis determined above had no significant trapping effect on F.intonsa female adults and vice versa.The cage experiments showed that the trapping number of both F.intonsa female adults and oviposition on the tomato plants with the synthetic aggregation pheromone blend of F.occidentalis had no significant differences compared with the control and vice versa.The results suggest that the aggregation pheromones of the two closely related species are species specific.It might be the reason for reducing the interspecific competition and then maintain the stable coexistence of two species.3.The interspecific interaction between F.occidentalis and T.palmi:the Y-tube olfactometer bioassays showed that the aggregation pheromones of F.occidentalis had no significant effect on female adults of T.palmi,but could repel T.palmi male adults.By contrast,the aggregation pheromones of T.palmi had no significant effect on both male and female adults of F.occidentalis.The field trapping experiments showed that the synthetic aggregation pheromone blend of F.occidentalis could significantly repel T.palmi adults.The cage experiments showed that the trapping number of T.palmi female adults on the tomato plants with the synthetic aggregation pheromone blend of F.occidentalis had no significant difference compared with the control and vice versa.The results suggest that the roles of major aggregation pheromone compounds in interspecific interactions between F.occidentalis and T.palmi are asymmetric.4.The interspecific interaction between F.intonsa and T.palmi:the Y-tube olfactometer bioassays showed that the aggregation pheromones of F.intonsa had no significant effect on female adults of T.palmi,but could repel male adults of T.palmi.By contrast,the aggregation pheromones of T.palmi had no significant effect on both male and female adults of F.intonsa.The field trapping experiments showed that the synthetic aggregation pheromone blend of F.intonsa could significantly repel T.palmi adults.The cage experiments showed that the trapping number of T.palmi female adults on the tomato plants with the synthetic aggregation pheromone blend of F.intonsa had no significant difference compared with the control and vice versa.The results suggest that the roles of major aggregation pheromone compounds in interspecific interactions between F.intonsa and T.palmi are asymmetric.In summary,the aggregation pheromones of F.occidentalis and F.intonsa are species specific,the two thrips species may reduce interspecific competition through specific recognition of aggregation pheromones and thus achieve stable coexistence in the field.The repel effect of F.occidentalis and F.intonsa on T.palmi could avoid direct competition between them and then achieve coexistence for the three thrips species.However,the repellency is also likely to lead to further expansion of F.occidentalis or F.intonsa,eventually leading to a competitive replacement of T.palmi.