The Effect of Trapa natans on the Number of Water Striders Gerris nepalensis and the Consequent Foraging Pressure on the Leaf Beetle Galerucella nipponensis

菱角Trapa natans對於水黽Gerris nepalensis數量之影響暨水黽對於葉甲Galerucella niponensis之捕食壓力

Tetsuo Harada ； Tomokazu Miyashita ； Michinori Imafuku

《台灣昆蟲》 31卷1期 (2011/03) Pp. 51-65

https://doi.org/10.6661/TESFE.2011005

摘要

本試驗假設菱角Trapa natans葉子能增加水黽數量，進而增加葉甲Galerucella niponensis之被捕食壓力，故此現象顯示水黽與菱角間可能具共生關係；因此本試驗由下列四方面進行研究：(1)菱角葉是否能吸引水黽？(2)雌水黽是否偏好菱角葉做為產卵處，即使是以聚苯乙烯製作之假菱角葉？(3)水黽是否能取食葉甲之胚胎及第一、二、三齡之幼蟲？(4)菱角是否能增加水黽越冬之存活率及次年春季之繁殖活動？試驗結果顯示，菱角葉能吸引水黽，特別是被葉甲傷害之菱角葉；即便有其他浮水植物，如水鱉Hydrocharis dubia或樟樹Cinnamomum camphora落葉，雌蟲仍偏好假菱角葉作為產卵處；水黽成蟲能取食葉甲胚胎，若蟲亦能有效率的捕食葉甲幼蟲；當試驗組之水黽與菱角葉共存，越冬存活率達90.7%且存活時間達三個月；然對照組水黽與假菱角葉共存，其存活率僅81.5%；試驗組水黽在次年春季來臨後之52日內，共產217顆卵；而對照組水黽在春季來臨後之38日內，產132顆卵；故可推論水黽Gerris nepalensis藉由捕食葉甲Galerucella niponensis之方式與菱角Trapa natans達成共生關係。

關鍵字

化學吸引 ； 滯育狀態 ； 春季繁殖 ； 產卵介質 ； 捕食壓力

並列摘要

It is hypothesized that the presence of water caltrop, Trapa natans leaves increases the number of Gerris nepalensis in its habitat and at the same time increases the foraging pressure on the leaf beetle, Galerucella nipponensis. This tends to support a possible symbiotic relationship of G. nepalensis to T. natans. The four questions in this study and their answers are as follows. 1) Can leaves of T. natans attract G. nepalensis? Based on the four experiments in this study, G. nepalensis was attracted to leaves of T. natans, especially those injured by the beetle, Gl. nipponensis. Even filter paper treated with liquids extracted from the leaves of T. natans injured by the beetle, Gl. nipponensis was preferred by G. nepalensis. 2) Do females of G. nepalensis prefer leaves from T. natans for their oviposition substrates over substrates made from other floating plants? When presented with artificial leaves made from polystyrene mimicking leaves of T. natans and other species of water floating plants such as Hydrocharis dubia and the fallen leaves of the camphor tree, Cinnamomum camphora, the females of G. nepalensis chose the artificial T. natans leaves as their oviposition substrates. Moreover when presented with real T. natans leaves and the artificial ones, they chose the real ones as their substrates. 3) Can G. nepalensis kill Gl. nipponensis by eating their embryos and the first, second and third instar larvae? Based on the survival rate, it is evident that adult G. nepalensis kill the embryos of Gl. nipponensis, and the later nymph stages of G. nepalensis can kill the younger stages of Gl. nipponensis very efficiently. 4) Is the success rate of overwintering and the reproductive activity that follows in the next spring enhanced by the accompanying of G. nepalensis with T. natans prior to overwintering? In the experimental group, in which G. nepalensis were accompanied with leaves of T. natans for 2 weeks before overwintering, 90.7% of the adult G. nepalensis survived and overwintered for 3 months. This was a little bit higher than the 81.5% survival rate by the control group, in which G. nepalensis were accompanied with artificial T. natans leaves made from polystyrene. Overwintered adults in the experimental group laid eggs in the following spring for 52 days on average, a significantly longer period than the 38 days for those in the control group. This led to a fecundity of 217 eggs on average compared to the 132 eggs laid by the control group. A symbiotic relationship between G. nepalensis and T. natans is possible against Gl. nipponensis especially based on the increasing foraging pressure from the water striders.

並列關鍵字

chemical attraction ； diapause posture ； spring reproduction ； oviposition substrates ； feeding pressure