無尾目兩棲類在黃緣步行蟲食性與生活史中的重要性

Importance of Anurans in Diet and Life History of the Ground Beetle Epomis nigricans

大部分兩棲類的昆蟲天敵多屬水棲性，牠們可捕食水中的蛙卵、蝌蚪或剛變態的小蛙。本研究中發現，陸棲性的黃緣步行蟲成蟲及幼蟲能捕食陸域環境中的小蛙，甚至比自身體型還大之成蛙。2007年夏季，我們於馬祖地區進行兩棲類相調查時，在黑眶蟾蜍腹部、貢德氏赤蛙後腳掌及地面上共發現3隻黃緣步行蟲幼蟲，帶回實驗室圈養及繁殖後，進行其食性、掠食行爲與生活史週期之研究。結果顯示：成蟲僅對蛙類活體展現掠食行爲。幼蟲的發育共有3個齡期，每一齡期的幼蟲須附著於蛙類體表取食，脫皮前才離開蛙體掉落地面。換言之，每1隻幼蟲至少須獵食3隻蛙類個體才可發育完成。幼蟲以大顎附著於蛙類體表吸食體液。取食之後，常造成蛙類傷口潰爛，有時也會造成組織或肢體的缺損，甚至個體的死亡。於室溫下（26~30℃），卵發育至成蟲平均爲26.4±1.1天。雖然黃緣步行蟲在台灣本島也有分布紀錄，但其掠食蛙類的行爲則尚未有所報導，需要野外更進一步的研究，以深入了解該物種的掠食行爲。

Most of the insects preying on amphibians are aquatic forms that feed on eggs, tadpoles, or newly metamorphosed juveniles in water. In this study we found that adults and larvae of the terrestrial beetle Epomis nigricans preyed on juvenile and adult frogs on land, whose sizes were usually bigger than those of the beetles themselves. In the summer 2007, we surveyed the amphibian fauna of the Matsu islands off the coast of mainland China, and observed three larvae of E. nigricans that preyed on adult frogs; one attached on the abdominal body wall of Duttaphrynus melanostictus, one attached on the tarsal skin of Hylarana guentheri, and the other one roamed on the ground. They were brought back to the laboratory and bred in captivity, and their diet, predatory behavior, and life cycle were investigated. The results showed that adults of E. nigricans preyed only on live frogs. For larvae at the 3 instar stages, each larva attached on a live frog for feeding, detached from the prey in ecdysis, and then preyed on another live frog for the next instar stage. In other words, a larva of E. nigricans requires preying at least three frogs during its 3 instar stages for developing to the adult stage. In predation the larva attached on frog s skin with its mandibles and sucked the prey s body fluids. The area attached became a festering lesion, in some cases, resulting in loss of tissues or legs, or even in death of the prey. It took the larvae for 26.4±1.1 days at room temperatures (26-30℃) to develop from eggs to adults. E. nigricans has been also recorded from Taiwan but its predation on frogs has never been reported. Further studies are required in the field to better understand the predatory behavior of this species.