The biology and interaction between ambrosia galls and galling-insects, Daphnephila (Cecidomyiidae), on Machilus (Lauraceae) in Taiwan

• Main Authors: Chen, Wen-Neng, 陳文能
• Other Authors: 楊曼妙
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/32996946704731831623

碩士 === 國立中興大學 === 昆蟲學系所 === 97 === Insect-induced galls are the deformation of plants initiated by insects which provide the immature insects shelters to acquire nutrition and protection to grow up. In some cases, gall inducing-insects develop intimate relationship with fungi and feed on the fungi rather than gall tissue. These galls are called ambrosia galls. The galling insect, fungus and host plant form a tritrophic interaction. This study will discuss how the fungi invade the cells, what the fungi are, and what the energy used in ambrosia galls. In Taiwan, some Daphnephila midge galls on Machilus spp. were found to be ambrosia galls recently. In this study, all of sixteen morphological species of Daphnephila spp. develop with mycelium in larvae cavities. Daphnephila is a diverse group in Taiwan and there are only five species named, each formed distinct galls on M. thunbergii. Culture and diagnosis of these fungi from the five different galls has found that they all have the fungus species Botryosphaeria dothidea (Ascomycota: Dothideomycetes: Botryophaeriaceae) identified by ITS sequences, which has been reported in other midge system as the fungus associate with ambrosia galls. Further survey of the fungal flora of other Daphnephila gall chambers discovered eleven different genera of fungi. The result suggests that Daphnephila may not be specific to certain fungal species. The tissue differentiation and levels of invasion by hyphae in ten galls were examined by paraffin sectioning. The ambrosia galls caused by Daphnephila are highly differentiated contrasted to the normal leaf tissue. Six layers of structure could be identified from outer-to-inner gall tissues, i.e., (i) the epidermis, (ii) cortex, (iii) vascular bundle, (iv) parenchyma between vascular bundle and sclerenchyma, (v) sclerechyma, (vi) nutritive tissue, including parenchyma in nutritive tissue and fungi zone. Variation from the above typical differentiation may be found in the banana-shaped galls on M. thunbergii which does not have the outer parenchyma zone and the inner parenchyma cells zone of the nutrition zone. All of the hyphae do not invade beyond the vascular bundles, and the nutrition layer (parenchyma cells) or sclerenchyma zone only accompanies intercellularly with the mycelium. As the nutrition hypothesis is the most plausible one depicted the adaptive significances of gall evolution, analysis of the energy among different types of galls with calorie test may help to understand whether there is a concordant pattern of evolution in their energy use. The result indicates a general pattern that galls of derived groups, contains higher energy based on the phylogeny of three main clades reported earlier. In dissection and observation of female abdominal segments, mycangia, a specific structure carrying spores, is on a distinct area in the eighth abdominal segment. Mycangia is covered by seventh enlarged segment with setae, and may have the function of carrying spores. It is also supposed to be a potential synapomorphy in Asphondyliini. Although the direct evidences of spore transmission were not clarified, my analyses provide information on the fungal association of the Daphnephila ambroia galls from various aspects which will be helpful for future study.