最近一項研究發(fā)現(xiàn)，有很多瓢蟲都會淪為寄生蜂——瓢蟲繭蜂的受害者,。目前已經(jīng)發(fā)現(xiàn)瓢蟲繭蜂為什么會把瓢蟲當(dāng)作孵卵器,，巫毒瓢蟲(zombie ladybugs)會對黃蜂易受攻擊的幼蟲起到保護(hù)作用，令食肉動物遠(yuǎn)離它們,，增加它們幸存下來的可能性,。
該研究成果6月21日發(fā)表在《生物學(xué)快報》上。這一研究發(fā)現(xiàn),，這種保護(hù)是要付出代價的：在仍活著的瓢蟲(而非死瓢蟲或者沒有瓢蟲的情況下)身上結(jié)繭的黃蜂幼蟲在蛻變成成年黃蜂后,，它們產(chǎn)的卵會更少。這表明黃蜂卵用來發(fā)育的相同資源,，也被用來控制巫毒瓢蟲,。
瓢蟲的悲劇
黃蜂的寄生方式早就受到科學(xué)家關(guān)注，它們并不是昆蟲界唯一一種采用這種方式的昆蟲,。例如,，寄生蜂Hymenoepimecis argyraphaga會在Plesiometa argyra蜘蛛的體內(nèi)產(chǎn)卵。然后幼蟲會咬破寄主的身體鉆出來,。寄主的心智也會被寄生蟲牢牢控制住,。被感染的P.argyra蜘蛛在死亡前，會在合適地點為黃蜂幼蟲織出一張蛛網(wǎng),。被特定菌類感染的巫毒螞蟻會在森林里四處游蕩,，直到正午它們才會停下來，用嘴死死咬住葉脈,，把自己固定住,。
日落時螞蟻會死去，菌柄會從螞蟻的腦袋上長出來,。但是蒙特利爾大學(xué)的研究生范妮-穆勒及其同事注意到,，即使瓢蟲繭蜂(D.coccinellae)幼蟲從瓢蟲的腹部鉆出來，它的寄主仍不會死,，這時瓢蟲處于半癱瘓狀態(tài),，偶爾會抽搐一下。這些科學(xué)家猜測,，活瓢蟲或許能保護(hù)黃蜂幼蟲不被食肉動物侵?jǐn)_,。為了驗證這一理論是否正確，研究人員在實驗室里養(yǎng)了4000多只瓢蟲，并讓黃蜂在不幸的瓢蟲體內(nèi)產(chǎn)卵,。然后他們耐心等待黃蜂幼蟲從寄主腹部鉆出來,，開始結(jié)繭。
瓢蟲保鏢
黃蜂幼蟲從寄主體內(nèi)鉆出來以后,，研究人員把這些巫毒瓢蟲和黃蜂幼蟲分成三組,。他們把第一組的瓢蟲從繭上取下來，只留下正在發(fā)育的幼蟲,。他們讓第二組的幼蟲繼續(xù)與瓢蟲呆在一起,，不過他們會把瓢蟲的腦袋碾碎，殺死它,。第三組一切照舊,，讓黃蜂幼蟲的繭繼續(xù)留在活著的瓢蟲身上。然后他們把這三個組合放到草蛉(一種食肉昆蟲,，喜歡吃黃蜂幼蟲)周圍,。每只草蛉可以單獨與一個繭呆15分鐘，研究人員記下它們成功偷取黃蜂幼蟲的次數(shù),。他們發(fā)現(xiàn),，由活瓢蟲保護(hù)的繭被吃掉的可能性僅為大約35%。當(dāng)黃蜂幼蟲繭沒有外物保護(hù),，或者與死瓢蟲呆在一起時,，它們被吃掉的可能性在85%到100%之間。
該研究還發(fā)現(xiàn),，與繭縛在一起的瓢蟲活得時間越久,，新生黃蜂的生育能力可能就越弱，這表明正在發(fā)育的黃蜂與它的寄主共享資源,。有意思的是,，幼蟲從瓢蟲腹部孵化出來前，瓢蟲的儲備越豐富,，它存活和保護(hù)幼蟲的時間就越長,。研究人員還需要進(jìn)行更多研究，才能確定黃蜂稍后是否會形成更多卵,，以便彌補(bǔ)它們與巫毒寄主分享的資源,。不過該研究還發(fā)現(xiàn)巫毒瓢蟲存在的另一項令人感到好奇的事情：大約有25%的瓢蟲會在寄生過程中存活下來，等到黃蜂幼蟲離開后,，它們會重新開始新生活,。（生物谷Bioon.com）
生物谷推薦原文出處：
Biology Letters DOI:10.1098/rsbl.2011.0415
The cost of a bodyguard
Fanny Maure, Jacques Brodeur, Nicolas Ponlet, Josée Doyon, Annabelle Firlej, éric Elguero and Frédéric Thomas
Host manipulation by parasites not only captures the imagination but has important epidemiological implications. The conventional view is that parasites face a trade-off between the benefits of host manipulation and their costs to fitness-related traits, such as longevity and fecundity. However, this trade-off hypothesis remains to be tested. Dinocampus coccinellae is a common parasitic wasp of the spotted lady beetle Coleomegilla maculata. Females deposit a single egg in the haemocoel of the host, and during larval development the parasitoid feeds on host tissues. At the prepupal stage, the parasitoid egresses from its host by forcing its way through the coccinellid's abdominal segments and begins spinning a cocoon between the ladybird's legs. Remarkably, D. coccinellae does not kill its host during its development, an atypical feature for parasitoids. We first showed under laboratory conditions that parasitoid cocoons that were attended by a living and manipulated ladybird suffered less predation than did cocoons alone or cocoons under dead ladybirds. We then demonstrated that the length of the manipulation period is negatively correlated with parasitoid fecundity but not with longevity. In addition to documenting an original case of bodyguard manipulation, our study provides the first evidence of a cost required for manipulating host behaviour.
