金龜子在各發育階段中消化道的構造變化

Abstract

完全變態昆蟲在幼蟲和成蟲期的外觀型態會非常不同，幼蟲隨著齡期增加而蛻皮直到進入蛹期，蟲體內外的器官組織會進行大量的改造以適應羽化成蟲後的棲地與食性的轉變。金龜子(Coleoptera: Scarabaeidae)在自然環境中扮演很重要的角色，除了幫助植物授粉和促進土讓內的物質循環外，他們也是在環境評估上的指標昆蟲。由於幼蟲和成蟲的食性不同，每個生長階段的消化道形態可能不同。然而，關於這方面相關的文獻非常少，因此我推測在幼蟲和成蟲階段具有不同食性的甲蟲會有不同的腸道形態，並認為腸道轉化會在蛹期發生。我選擇了5種金龜子作為描述整個生活史的腸道變化的觀察對象：Oryctes rhinoceros、Thaumastopeus shangaicus、Protaetia orientalis、Protaetia inquinata和Protaetia formosana。這些甲蟲在幼蟲期居住於腐木或堆肥內，以食用有機質維生，而成蟲以花蜜、果實等較軟的植物組織維生。此外使用甘藷龜金花蟲 (Cassida circumdata,Chrysomelidae)與金龜子比較整個生長期的腸道變化是否跟幼蟲和成蟲食性的轉變有關。每個階段皆至少各剖3隻個體，並使用顯微鏡觀察消化道結構，拍照並說明各個階段的消化道特徵。從實驗結果發現金龜子在蛹前期的消化道會從幼蟲期轉變成成蟲期的腸道，進行腸道的大改造，但有一些構造如後腸的生物膜仍會保留在成蟲腸道內。在甘藷龜金花蟲的生活史中，腸道並沒有隨著生長階段進行較大的改變。這些資訊可以為變態提供新的見解，包括金龜子蛹期的消化道形態變化的過程以及這些物種可能的共生微生物傳播途徑。

Holometabolous insects like beetles are morphologically very different between larvae and adults. They grow through successive molts until the pupa stage, when their tissues and organs are modified to adapt to the shift of habitats and feeding habits. The scarab beetles (Coleoptera: Scarabaeidae) play an important role in the environment. In addition to pollination and promoting the circulation of materials in the soil, they are also indicator insects for environmental assessment. The morphology of the digestive tract in each life stage may be different, as the diets of the larvae and adults are different. However, there is little literature about this. I hypothesize that beetles with different diets in the larval and adult stage will have significantly different gut morphologies, and wanted to observe these changes develop during pupation. I chose these Scarabaeidae species as the focus of my thesis: Oryctes rhinoceros, Thaumastopeus shangaicus and Protaetia spp., where the larvae eat wood, soil, or compost while the adults feed on soft plant matter, tree sap, and rotting fruits. I compared these to the tortoise beetle, Cassida circumdata (Chrysomelidae), which feeds on leaves as both larva and adult, to compare their gut morphology to see if the digestive tract changes dramatically to satisfy changes in diet. I dissected three beetles of all species in each stage, observing the structures in detail on the microscope, taking photos and illustrating their digestive tracts. I found there are dramatic changes of the digestive tract in scarab beetles during the pupal stage, although some structures like a microbial biofilm are retained from the larval stage. In the leaf beetles, the gut did not change. This information can provide new insight into metamorphosis, including the possible symbiont transmission routes for these species. The illustrations of what occurs during pupation are novel contributions to this field.