Dussourd David E
Department of Biology, University of Central Arkansas, Conway, AR 72035, USA e-mail:
Oecologia. 1997 Oct;112(3):362-369. doi: 10.1007/s004420050321.
Cabbage loopers, Trichoplusia ni, cut a narrow trench across leaves of plants that release exudate, then feed distal to the trench in an area of reduced exudation. The larvae do not normally trench plant species such as plantain, Plantago lanceolata, that lack exudate. To determine what cues elicit trenching, I reared larvae to the final instar on plantain, then applied test solutions to their mouthparts during feeding. Loopers that received latex from Lactuca serriola (Asteraceae) or phloem exudate from watermelon, Citrullus vulgaris (Cucurbitaceae), often responded by cutting a trench in plantain, even though these larvae had not previously encountered exudate nor previously trenched. Loopers that were allowed to trench and feed on L. serriola for 1 day prior to the assay subsequently cut trenches in plantain more frequently and in response to more fluids, including a viscous solution of polyethylene glycol and latex from a non-host, poinsettia (Euphorbia pulcherrima). Subsequent bioassays with larvae reared entirely on plantain tested whether bitter cucurbitacins or gelation are essential cues for trenching. Sap from non-bitter cucumber plants (Cucumis sativus) caused larvae to trench, showing that cucurbitacins are not required to induce trenching. Loopers also trenched after receiving cucumber sap that did not gel due to the addition of mercaptoethanol. An extract of sap lacking the proteins that cause gelation likewise triggered trenching. Further fractionation revealed that cucumber sap and also butternut squash sap (Cucurbita moschata) contain trenching stimulants that are small (molecular weight < 3,000) water-soluble molecules.
粉纹夜蛾（Trichoplusia ni）会在能分泌渗出液的植物叶片上切割出一条狭窄的沟，然后在渗出液减少的区域，即沟的远端取食。幼虫通常不会在像车前草（Plantago lanceolata）这种不分泌渗出液的植物上开沟。为了确定引发开沟行为的线索，我将幼虫饲养到最后一龄期，使其以车前草为食，然后在其取食时将测试溶液涂抹在它们的口器上。接受来自刺莴苣（Lactuca serriola，菊科）的乳胶或来自西瓜（Citrullus vulgaris，葫芦科）的韧皮部渗出液的粉纹夜蛾幼虫，常常会通过在车前草上切割出一条沟来做出反应，尽管这些幼虫之前从未接触过渗出液，也从未进行过开沟行为。在实验前一天被允许在刺莴苣上开沟并取食的粉纹夜蛾幼虫，随后在车前草上切割沟的频率更高，并且对更多液体做出反应，包括聚乙二醇的粘性溶液以及来自非寄主植物一品红（Euphorbia pulcherrima）的乳胶。随后用完全以车前草饲养的幼虫进行的生物测定，测试了苦味葫芦素或凝胶化是否是开沟行为的关键线索。来自无苦味黄瓜植株（Cucumis sativus）的汁液会使幼虫开沟，这表明诱导开沟行为并不需要葫芦素。在接受因添加了巯基乙醇而不会凝胶化的黄瓜汁液后，粉纹夜蛾幼虫也会开沟。缺乏导致凝胶化的蛋白质的汁液提取物同样引发了开沟行为。进一步的分级分离表明，黄瓜汁液以及南瓜（Cucurbita moschata）汁液都含有能刺激开沟的物质，这些物质是小分子（分子量<3000）的水溶性分子。
