鹽類對埃及斑蚊和台灣鋏蠓卵黑化之影響與耐旱之研究

Abstract

埃及斑蚊 (Aedes aegypti (Linnaeus)) 與台灣鋏蠓 (Forcipomyia tai-wana (Shiraki)) 都是造成台灣公共衛生問題的重要害蟲，透過吸血引起人體產生紅腫或過敏反應，甚至傳播疾病。針對這兩種害蟲的防治過往主要著重於幼蟲與成蟲階段，卵期相對未受到重視。因此本研究著重於卵期防治，探討鹽類對埃及斑蚊和台灣鋏蠓的卵殼黑化的影響，及台灣鋏蠓卵的耐旱能力。結果顯示添加鹽類的產卵基質雖對埃及斑蚊與台灣鋏蠓有忌避產卵的效果，但若懷卵雌蟲將卵產於含鹽類基質上則無法黑化，亦無法順利孵化 (無效卵)。當埃及斑蚊產於含 0.5M 的 NaCl、KCl 與 MgCl2 鹽類的環境當中的卵黑化率分別為 3.96%、3.40% 以及 7.89%，且孵化率除 MgCl2 為1.17%，前兩者皆為 0%；而產於 CaCl2 及 K2SO4 鹽類中的卵黑化率約為 38 ~ 39%，而產於 (NH4)2SO4 鹽類的卵有 71% 黑化率，但孵化率皆為 0%。雖然產於 MgSO4 鹽類組別的卵可以全數黑化，但其黑化卵在二次水中的孵化率僅約 67%，明顯低於控制組 (孵化率 > 90%)。此外，在埃及斑蚊卵內之過氧化酶 (黑化相關酵素) 活性試驗，結果顯示黑化卵之酵素活性顯著高於無法黑化的白卵，因此推論額外添加的鹽類可能直接或間接影響胚胎內黑化相關酵素的活性。台灣鋏蠓產於含鹽類洋菜膠培養基的卵黑化率約在 0 ~ 40%，與控制組相比皆有顯著差異。而台灣鋏蠓卵的耐旱程度研究，利用吸水性良好的石膏做為卵的培養基質，將產出後 24 小時的卵挑至含水量 5 ~ 50% 的石膏盤上，發現含水量 20% 以上的石膏盤才能使卵不乾扁且孵化。此外，將卵保存於含水量 20% 與 30% 石膏盤上，並放置於 17℃ 與 27℃ 環境下，試驗結果顯示雖然卵可以維持八週不乾扁，但能夠孵化的卵幾乎都在前三週孵化完畢，此一結果顯示台灣鋏蠓的卵不如埃及斑蚊卵可以耐乾旱及長久保存。而鹽類影響斑蚊與鋏蠓卵黑化的相關機制有待進一步探究。

Both Aedes aegypti (Linnaeus) and Forcipomyia taiwana (Shiraki) are important pests inducing serious public health problems in Taiwan, such as allergic reaction and spreading diseases through bloodsucking. Though there are numerous control strategies, the eggs of mosquito did not receive much focus as the control target as that of larvae and adult stage. Therefore, my studies address the effect of salts on egg melanization and desiccation tol-erance of Ae. aegypti and F. taiwana. Our results showed that salt-containing milieu may deter the oviposition of both pests and the eggs laid on the salt-containing site are unable to melanize and hatch. In Ae. aegypti, the eggs laid on 0.5 M of NaCl, KCl and MgCl2 solution were barely tanned and unable to hatch. Although the melanization rate of eggs in CaCl2 or K2SO4 and (NH4)2SO4 were around 38-39% and 71% respectively, those eggs were all unable to hatch. The eggs laid in MgSO4 solution can be 100% melanization, their hatching rate was about 67%, which is still much lower than that in the control (> 90%). The peroxidase activity of dark eggs is much higher than that of white eggs, indicating that salts may have negative impact on melanization enzyme. In F. taiwana, the eggs laid on agar plate containing various con-centrations of salts were also barely melanized (melanization rate about 0-40%) and unable to hatch. When F. taiwana eggs laid in agar plate for 24 hours by gravid female were transferred to gypsum plate containing 5-50% water, only those eggs placed at > 20% water content plate can survive after one week. Though the egg shape can keep intact in gypsum plate with 20% or 30% water content under either 17 or 27oC for 8 weeks, no larva hatched after third week. These results suggested that F. taiwana eggs could not long sustain in dry environment as that of Ae. aegypti eggs. In summary, salts exert significant impacts on the melanization of both Ae. aegypti and F. taiwana egg, nevertheless, the mechanism remains further explored.