螞蟻對甲基丁香油誘蟲器內果實蠅樣本之影響

Abstract

甲基丁香油誘蟲器常用於監測東方果實蠅 (Bactrocera dorsalis) 之族群密度，為詳實反應其田間密度，許多研究皆致力於探討誘引效力的相關物化因子，例如懸掛高度或誘引物質改進，但影響果實蠅密度估算之外在生物因子似乎較少受到重視。許多研究，包括許多第一線改良場人員，皆指出果實蠅誘蟲器中出現大量螞蟻，但對於螞蟻於誘蟲器中所造成之影響則不得而知，主要因應方式大多僅建議進行防蟻措施。因此本研究以此議題為主軸，探討螞蟻存在是否影響果實蠅誘蟲器之樣本數目 (是否影響果實蠅密度監測之準確性)，與影響螞蟻進入陷阱之因素。本研究以懸巢舉尾家蟻 (Crematogaster rogenhoferi) 為例，首先探討舉尾家蟻是否受甲基丁香油誘引而進入誘蟲器：以冷凍處理與有、無含毒甲基丁香油 (TME、ME) 處理之果實蠅供舉尾家蟻選擇，經12小時後雖三處理數目皆有減少，但冷凍處理之果實蠅數目均較TME及ME處理低，顯示舉尾家蟻對甲基丁香油並無明顯偏好性存在，且只於TME處理發現大量舉尾家蟻死亡，此現象與誘蟲器中死亡螞蟻如出一轍，可能為甲基丁香油中添加之乃力松 (naled) 毒害造成。後續進一步探討螞蟻進入誘蟲器對樣本造成影響是否有穩定時間點可循，室內結果至14天試驗結束時，誘蟲器中果實蠅數目幾無減少，每日皆有不同數目螞蟻死亡，推測可能含毒甲基丁香油於室內耗損極小，對螞蟻而言進入誘蟲器之門檻仍與試驗開始時幾乎相同。因此重新於室外環境後進行實驗，結果與前述室內試驗相似，無法藉由螞蟻死亡數及誘蟲器剩餘果實蠅數目推斷螞蟻何時進入誘蟲器。此干擾現象可能不受乃力松強弱影響，而是取決於螞蟻對食物之需求與否。最後於苗栗縣及新北市數樣點安裝懸掛鐵絲上以黏蟲膠處理之誘蟲器與慣行誘蟲器各一，每兩周觀察誘蟲器內果實蠅及螞蟻種類及數量，觀察是否能阻止或減少螞蟻對樣本的干擾。結果發現有多種螞蟻可於慣行誘蟲器中發現，並以舉尾家蟻屬、皺家蟻屬 (Tetramorium)、管琉璃蟻屬 (Ochetellus) 之螞蟻為大宗，且果實蠅破損比例顯著高於黏蟲膠處理組別，顯示黏蟲膠能防止螞蟻進入誘蟲器以及樣本破損的發生達近一年。本研究討論相關試驗受螞蟻干擾之潛在影響，並測試可適用於誘蟲器之防蟲資材，盼對於臺灣果實蠅相關試驗上有所幫助。

Methyl eugenol trap is one of primary methods for controlling and monitoring several fruit fly species including oriental fruit flies (Bactrocera dorsalis), a pest that causes serve ecological loss to tropical fruit trees. To accurately reflect field density of B. dorsalis, numerous studies focused on the intrinsic factors such as attractiveness of methyl eugenol. Extrinsic factors that may influence accuracy of fly density monitoring, however, receive less attention. The present study is therefore to explore the long term effect of the presence of ants on the number of B. dorsalis in the methyl eugenol traps. Relevant issues regarding attractiveness of methyl eugenol to the ants and time point(s) when the ants initiate intensive foraging activities in the traps were also discussed. B. dorsalis killed by freezing (FZ), toxicant (naled) methyl eugenol (TME) and pure methyl eugenol (ME) were offered to the acrobat ants (Crematogaster rogenhoferi) under a non-choice test, and results showed that the ants fed on the three types of B. dorsali with slight preference on FZ over others. High number of dead ants were found in TME treated groups, suggesting that TME may impose negative effects on the ants after consumed. Under both lab and field conditions, the acrobat ant nests were connected to McPhail trap in which a cotton containing TME and freshly killed B. dorsalis were placed, and number of fruit flies remained and dead ants in trap were recorded on a daily basis for two weeks. Results indicated that number of fruit flies was nearly the same after 14 days in lab conditions (walk-in chamber), but not those in field conditions where ants did consume on certain proportions of the fruit flies. Along with the finding of the number of dead ants being constantly high in both conditions, the presence of the ants in the traps as well as time point of the ants initiating foraging activities seem not affected by the amount of TME. Field experiments were also conducted in Miaoli County and New Taipei City to compare the number of B. dorsalis between conventional and glue-coated (string) methyl eugenol traps. It was observed that the proportion of intact fruit flies in the conventional traps is significant lower than the glue-coated ones, and number of ants per trap is predominantly higher in the conventional traps than in the glue-coated traps. Most of ant species observed were Crematogaster, Tetramorium and Ochetellus spp. Such patterns suggest that reduction of number of fruit flies in conventional traps likely result from foraging ants, and glue-coated trap can effectively prevent ants from entering into traps.