Differences in Gall Induction of Flower-like Galls on Haloxylon by Psyllids (Hemiptera: Aphalaridae), and the Emergence of Corresponding Parasitoids

Saxaul is a kind of dominant perennial psammophyte that widely distributes in arid and semi-arid desert areas, and it has multiple functions in preventing desertification, especially in windbreak and sand fixation. Various gall inducers induce galls on the saxaul, including the flower-like gall. Parasitoids have great potentiality in controlling gall inducers. However, studies about gall inducers and parasitoids of flower-like galls on Haloxylon, as well as the parasitic efficacy of the parasitoids, are rarely reported. In this study, the flower-like galls were observed on Haloxylon ammodendron and H. persicum in Fukang, Xinjiang, China. Two types of flower-like galls were found on H. ammodendron, while only one type was found on H. persicum. In total, five species of gall inducers and three species of parasitoids were obtained from the galls mentioned above. All the galls were induced by Caillardia (Hemiptera: Aphalaridae), which were mostly bivoltine in Fukang. Besides, their parasitoids Psyllaephaguscaillardiae and P. longiventris could be observed on all the types of galls. Additionally, correlative studies on the parasitization indexes demonstrated that all the dominant parasitoids of diverse flower-like galls were P. caillardiae, which were slightly more in number than the P. ogazae discovered in the flower bud-like galls. In addition, the relevance between the emergence or lifespan of parasitoids and temperature was also investigated. The results showed that the number of parasitoids emerging decreased rapidly after a period of enhancement with the increase of temperature, including an optimum temperature, while the lifespan of wasps gradually shortened with the temperature rising. Our results highlight the importance of the biological investigation of parasitoids in the gall inducers lived in closed galls, which may provide critical evidence for us to understand its potential application in biological control.