產卵經驗與寄主隔離對綠豆象寄主偏好之影響

Abstract

為了探討綠豆象(Callosobruchus chinensis （L.）)在經歷不同產卵經驗後，對寄主偏好的改變，而做此試驗。綠豆象為內食性昆蟲，成蟲孵化後不再取食，幼蟲生長的營養來源，由雌蟲產卵時決定，因此產卵選擇會影響到子代的存活。綠豆象之寄主為豆科植物，在無選擇產卵試驗時，對紅豆、和綠豆之接受度，並無差異；然而有選擇試驗時，則偏好紅豆產卵。影響雌蟲產卵因子有許多曾被提出，例如寄主種類、寄主大小、寄主數量、遭遇前後不同寄主的情況下等。本試驗主要分成四個部分探討雌蟲產卵偏好。（一）為成蟲產卵經驗對偏好之影響，結果顯示在綠豆上產卵經驗，並不會提高雌蟲對綠豆之偏好，顯示紅豆寄主有很強的產卵訊息刺激，即使經過綠豆產卵經驗，也不會改變對紅豆的偏好。因此，進一步檢驗不同產卵經驗，對寄主接受度之影響，發現先產卵在偏好較低的寄主，再提供偏好較高之寄主時，雌蟲很快接受產卵；若產卵在原本偏好程度較高之寄主，再提供偏好較低之寄主時，雌蟲則需要花較多時間，才能接受產卵。從成蟲產卵經驗證實綠豆象具有學習經驗，表現在寄主接受度上。（二）隔離寄主處理對產卵偏好之影響，結果顯示寄主隔離會造成載卵壓力。在未達到棄卵程度前，提供寄主產卵，綠豆象會加快產卵速率，以釋放壓力。此時提供兩種寄主豆產卵時，依然偏好紅豆產卵，隔離寄主時間愈久，並未提高在綠豆上產卵百分比。無論寄主資源與否，雌蟲皆偏好在紅豆產卵，因此再檢驗雌蟲經過寄主隔離後，所產下第一顆卵，依然偏好紅豆產卵，說明寄主刺激較載卵壓力刺激更能影響產卵決定。（三）為同種間干擾、競爭經驗對偏好之影響。結果顯示在無寄主情形下，經歷與其他雌蟲存在之經驗，並不會改變產卵選擇，推測經驗影響產卵選擇必須是在有寄主資源的情形下。因此分別提供紅豆或綠豆競爭資源經驗，雌蟲並未因有經歷競爭經驗，而提高對綠豆之偏好。（四）探討綠豆象種內競爭是否會改變其偏好，結果顯示雌蟲數目增加，會造成產卵速率減慢，無論資源充足與否，同樣並未提高對綠豆產卵偏好，因此綠豆象產卵偏好受到寄主種類影響最深。

The main goal of this study is to understand the changes of host preference based on the previous experience. Because Callosobruchus chinensis is an endophagous insect, and adults do not feed, the nutrition resources of this species is totally determined by the choice of the female. Therefore, the oviposition of females affects survival of offsprings. The host plant,of Callosobruchus chinensis, is the plant of Legurninosae. Females lay eggs on the seed. In the no-choice tests, females accept azuki bean or mung bean as host without significant difference in preference. However, females prefer to oviposit on azuki bean when it can choose between the two hosts. There are many factorses such as oviposition experience to affect oviposition. The study is composed of four portions to explore female ovipositional preference. Firstly, the previous ovipositional experience did not increase the host preference on mung bean. Female showed significant host preference on azuki bean even they had oviposited on mung bean. However, the ovipositional experience on azuki bean did not increase the host preference on it. Furthermore, we tested the effect of different ovipositional experience on host acceptance. The result showed that females shortened the acceptance time on azuki bean when they had ovipositional experience on mung bean. On the contrary, females needs more time to accept mung beans for oviposition when the situation was reversed. Based on these results, we confirmed the learning ability of Callosobruchus chinensis on host acceptance. Secondly, we investigated the effects of host deprivation on host preference. It was clear that host deprivation did cause the pressure of egg load. Although females speeded up to oviposit on host in order to release the pressure, they still preferred to lay eggs on azuki beans. The females did not increase oviposition on mung bean even with 24 hours of host deprivation. Regardless of host resources, females preferred to oviposit on azuki beans. Females would lay the first egg on azuki bean right after a period of host deprivation. The result implied that the innate host preference could not be changed by host deprivation. Thirdly, we explored the effects of interference and competition experience on host preference. The results showed that females did not change ovipositional preference with the interference experience of being together with other females without host resource. However, females with competitive experience did not increase the host preference on mung bean when they were offered with azuki beans and mung beans. Fourthly, the main issue is the effect of intraspecific competition during oviposition on host preference. We found that females did slow down to oviposit while the numbers of females in competition did increase. The competition did not increase its preference on mung bean regardless the quantity of host resource. Therefore, we could conclude that the most prominent factor to determine the host preference was built in the host species.