Nutritional use of Daphnephila gall midges on Machilus thunbergii and organisms associated with their galls

• Main Authors: Liang-Yu Pan, 潘亮瑜
• Other Authors: 楊曼妙
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/85914181757108169109

博士 === 中興大學 === 昆蟲學系所 === 103 === Daphnephila is a common group of Cecidomyiidae in the evergreen broadleaf forests of Taiwan. Diverse galls induced by different species of Daphnephila often concurrently exist on the same host species demonstrating a striking niche divergence and resource sharing. The galls induced by D. truncicola, D. taiwanensis, D. sueyenae, D. stenocalia, and D. ornithocephala on Machilus thunbergii were examined : (1) to know whether the life cycle differs among various Daphnephila gall midge species accompanying the same host M. thunbergii; (2) to test the nutritional adaptation hypothesis by stable isotope; (3) to examined the galls to verify the hypothesis that the morphology of galls is an expression of the extended phenotype of the respective gall-inducing insect; (4) to establish the fungus flora in different gall midge development stage by isolating the fungi inside galls from the immature to mature stage; (5) to record the parasitoids and cecidophagous predators associated with Daphnephila galls. Results are as following. (1) Populations of four leaf-gall inducing Daphnephila species were tracked on 105 M. thunbergii trees at four sites on Mt. Datun in Yangmingshan National Park in Northern Taiwan for seven years (2004–2011). Daphnephila populations recognized as either the winter or the spring emergent group could take advantages of two bud bursting seasons, either winter (January–February) or spring (March–May), based upon the availability of their oviposition time and location and they use either the vegetative leaves of the winter mixed buds with inflorescence and vegetative shoots or the spring vegetative buds producing no reproductive organs. Daphnephila populations show two types of life cycles: one-year type and two-year type, the latter with an extended diapause to the second year of the first-instar larva. Tracing the development of eggs from the same batches, I found the offspring did not always follow the life strategies of their parents. (2) Gall tissues had higher carbon isotope contents than the galled leaves. Consequently, a relocation of carbon isotope composition occurred when gall formed and a typical food chain relationship is revealed. (3) Based on their length―width ratio, the materials were grouped into either fleshy (those induced by D. taiwanensis and D. sueyenae) or slim (those induced by D. truncicola, D. stenocalia, and D. ornithocephala) types of galls. The numbers of reserve and nutritive cell layers in galls were greater in the stem galls induced by D. truncicola, similar to those in the fleshy leaf galls, but were fewer in other slim leaf galls. The gall tissues retained some property characteristic from plant tissues, such as the boundary-parenchyma-like parenchyma in stem galls and the bundle sheath in leaf galls. (4) Based on the fungal taxa isolated from the larval chambers, the dominant fungi in mature galls was B. dothidea while in immature galls were Fusarium spp. Regardless sampled localities, the above dominant status of fungal groups remained the same, whereas the non-dominant fungal taxa varied among different areas. (5) The major parasitoids are Platygaster sp. and Eupelmus sp. Five species of animals are newly recorded to be cecidophages on Daphnephila galls, i.e. the Formosan rockmonkey (Macaca cyclopis), the Taiwan blue magpie (Urocissa caerulea), the Formosan red-bellied tree squirrel (Callosciurus erythraeus), and two species of Noctuidae larvae. These animals are facultative cecidophages and usually feed on the leaves, buds or fruits of host plants. They selectively nibble at the gall tissues in winter or early spring, indicating that they may use galls as a supplemental food when their usual food resource is low. In conclusion: (1) this is the first survey on the cohort of M. thunbergii associated with Daphnephila galls in Taiwan. Synchronizing utilization of the host resources and similar life cycles were found among the four leaf-galling Daphnephila species; (2) the results of stable carbon isotope suggests that the selection forces may toward smaller sizes for galls and decreasing carbon isotope contents with an optimal relationship; (3) the shapes, structure, nutritive tissues, energy levels, and multiple coexisting fungal taxa within galls reinforce that they are extended phenotypes of the respective gall-inducing Daphnephila species and they represent adaptive evolution of Daphnephila on M. thunbergii; (4) Botryosphaeria dothidea is the primary associate and possibly a symbiont. The different fungal taxa isolated from mature galls induced by the same Daphnephila populations suggest that these Cecidomyiidae may use different species of secondary fungal associates to possibly enhance their nutrition; and (5) this study newly recorded the cecidophages behavior of two endemic vertebrate.