Biosystematics of the galling midge Daphnephila (Diptera:Cecidomyiidae) on Machilus spp. (Lauraceae) in Taiwan

Abstract

造癭昆蟲多為單食性或寡食性，具有寄主及寄生器官專一性，因此蟲癭形狀被視為造癭昆蟲表型的延伸，代表造癭昆蟲種類。本研究以寄生於台灣樟科楨楠屬植物上的雙翅目癭蚋科Daphnephila屬造癭癭蚋為材料，從蟲癭形態、造癭昆蟲分子及形態特徵，以及寄主植物等資訊，探討其分類與親緣關係，並且觀察葉部癭蚋之生殖行為，建立基礎生物學資訊。本研究檢視台灣楨楠屬的所有物種，採集其上發生的蟲癭，依據蟲癭形態、發生位置以及寄主植物物種等資訊，可分為38個形態種，再依其相似性，可歸納為8個蟲癭系列(鼠狀、棒狀、鳥頭狀、壺狀、倒卵狀、小壺狀、梭狀以及針狀)，系列間蟲癭形狀有明顯差異，而系列內差異較小。以粒線體基因分析，結果顯示相似蟲癭形態種之造癭癭蚋大都為單系群，且各單系群間彼此有明確分化現象，分化程度界於1.3%~14.3%之間，其中僅有極少數在2%以下，且都集中在棒狀系列中；形態研究顯示寄生於枝條與葉部的癭蚋，兩者在幼蟲胸骨形狀及成蟲外生殖器有明顯差異，但是在枝條蟲癭內或葉部蟲癭之內的各形態種的癭蚋差異較不明顯，但仍有可區辨的微細差異。綜合各項結果，Daphnephila屬癭蚋目前至少可區分出9種(包含已命名之5種)。枝條癭有4種，除了原已命名之D. truncicola，另有3未命名種。葉片癭部分較為複雜，鼠狀系列為一複合種，已命名者有D. taiwanensis，但在分生方面顯現仍有分化中之待釐清的隱藏種；葉片棒狀系列、壺狀系列與鳥頭狀系列蟲癭之造癭者整體呈現複合種的關係，除已描述的棒狀造癭者D. stenocolia以及鳥頭狀造癭者D. ornithocephala，尚包含多個分化中的類群，其中壺狀明顯自成一支，應可確認已獨立分化為新種，其他各型則仍待釐清；而小壺狀系列則應與倒卵狀系列之造癭者D. sueyenae為同一物種。本研究針對標本較為齊全之2新種進行描述，即香楠及霧社楨楠枝條梭狀I型D. sp.1及葉片壺狀D. sp.2。針對葉部癭蚋生殖行為觀察結果，顯示成蟲生殖契合寄主植物物候，雌蟲於初展開的嫩葉產卵，可能藉由費洛蒙吸引雄蟲前來交配，而蟲癭的著生模式決定於雌蟲的產卵行為。整體而言，Daphnephila的各蟲癭系列(除了小壺狀系列以外)可對應各不同癭蚋物種，但系列內的癭形態種則不一定能直接判定為不同癭蚋物種，須從多方面的證據掌握其整體變異，才能綜合釐清分類情形。

Most of gall-inducers are monophagus or oligophagus, which utilize a narrow spectrum of host plants and organs. Diversity of gall inducers and the specific relationship between galling insects and host plants are considered as a consequence of adaptive radiation. Galls could be considered as extension of phenotypes of the gall indusers. This study focused on the relationship between Daphnephila spp. (Diptera: Cecidomyiidae) and Machilus (Lauraceae) in Taiwan based on morphological characters of insect and galls, molecular, and biological data in order to clarify the galler taxonomy and the phylogenetic relationship. After examining all the plant species of Machilus in Taiwan, the acquired galls were sorted into 38 morphological species based on their gall shape, galling position, and host plant information. Galls with similar shaped could be further groups into 8 series, i.e., spindle-shaped, needle-like, urn-shaped, little urn-shaped, obovate, club-shaped, bird-head-shaped and ovoid gall serieses. There are significant differences among gall seires but smaller variation within each gall series. Molecular analansis based on gene revealed that most of gall midges with similar shapes (gall morphospecies) are monophyletic group. Clear differentiation ranging from 1.3% to 14.3% exists between each group and only a few less than 2% which is mainly belong to club-shaped series. Morphological differences were found between midges from stem and leaf galls, espcieally on larval spatula and adult genitalia. Only trievial differences could be found for the midges within stem or leaf galling groups. The overall evdiences suggest that there are at least 9 species in Daphnephila, including 5 named species (Daphnephila sueyenae, D. ornithocephaia, D. stenocalia, D. taiwanensis, D. truncicola), and 4 new species. The stem gall midges inculed 1 named species (D. truncicola) and 3 unnamed species. The taxonomy of leaf gall midges are more complicated. The mouse-like gall series is a species complex, which contain D. taiwanensis and a cryptic species. The club-shaped, bird-head-like, and the urned-shaped series formed another species complex, including two named species (D. stenocalia and D. ornithocephala) and a new species (urned-shaped gall inducer). The midges of little urn-shaped gall series are the same species of midges belonging to obovate gall series (D. sueyenae). Field observation on midges indicates the clear synchronization between reproduction of adults and phenology of host plants. Females may secrete pheromone to mate with males and the galling position and patter are determined by females. To sum up, the gall shape series (except for little urn-shaped gall series) reflect the taxonomic status at species category of Daphnephila gall midges, whetheras the variability with gall shape series may not always reflect the species status. It is necessary to obtain eveidences from differet aspects and to integrate the overall variation for making correct taxonomic determination for the gall midges.