寄主經驗與隔離對四紋豆象產卵接受度之作用

Abstract

四紋豆象為內食性昆蟲，其一生能量來源受限於親代產卵時所挑選的寄主提供的養分，故雌蟲的產卵選擇會直接影響子代的適存值。過去的研究報告指出，雌豆象成蟲利用相對法則檢視寄主品質，以決定是否產卵於寄主豆上；而且在非選擇性試驗中，雌蟲產於綠豆或紅豆的卵數相等；但在紅、綠豆選擇性試驗中，雌蟲則偏好產卵於紅豆。本研究透過觀察雌蟲在全紅豆組、全綠豆組以及紅、綠豆混合組中的產卵行為來釐清產卵行為和寄主偏好之間的關係。試驗發現雌蟲在全紅豆組和全綠豆組中，產卵前處理寄主的時間及拒絕乾淨寄主豆的頻率相同；但雌蟲對混合組中的綠豆之產卵前處理時間以及拒絕乾淨寄主豆的頻率顯著高於其他處理組。由此行為推測經歷紅豆的寄主經驗會降低產卵於綠豆。意即寄主經驗會影響四紋豆象的寄主辨識。另外，透過人為操縱使雌蟲在成蟲期獲得不同形式寄主經驗的方式，發現相較於僅接觸紅豆的經驗，經歷產卵於紅豆的經驗會導致雌蟲後續降低產卵於綠豆。且在連續 12 小時的寄主接受度檢驗中，透過比較最終累積產卵量，仍然可以發現產卵於紅豆經驗的效應存在；連續 24 小時的寄主接受度檢驗中，此效應則消失。然而，即使是在經歷產卵於寄主的經驗後，再遭遇長達 3 天的寄主隔離，造成雌蟲載卵壓力提高，但產卵於紅豆的經驗，致使後續降低產卵於綠豆的效應仍然存在。

Callosobruchus maculatus (F.), the cowpea weevil, is an endophagous insect. It has been reported that the adult female weevils measured the quality of host beans by following a relative rule, and then either to oviposit or leave these beans. The female weevils oviposited on mung beans as well as adzuki beans in no-choice test, while they preferred adzuki bean over mung bean in choice test. To study the relationship between oviposition behaviour and host preference, three treatments (A: pure adzuki beans; M: pure mung beans; Mixed: mixed adzuki beans with mung beans) were provided to the female. We found that the female’s handling time before ovipositing on mung beans in treatment M and adzuki beans in treatment A were the same, but it is longer on mung beans in Mixed treatment than that of treatment M. Moreover, the rejection frequency on mung bean in Mixed treatment was higher than the others. The behavioural analysis of these three treatments showed that the host-experience on adzuki beans reduced ovipositon on mung beans. The result may imply that host-experience affects host discrimination in C. maculatus. Based on the results of different levels of host-experience, it was host-oviposition-experience but not host-contacting-experience to cause the reduced oviposition on mung beans subsequently. Furthermore, the effect of adzuki bean experience could remain effective based on the accumulative number of eggs within 12 hours, but disappeared in 24 hours host-acceptance-test. The adzuki bean experience even remained to be effective on host acceptance after 3 days of host-deprivation. In spite of increasing oviposition rate, host-deprivation did not totally eliminate the influence of adzuki bean experience.