家蚕幼虫取食策略.md

Diet choice: The two-factor host acceptance system of silkworm larvae

今天介绍的这篇文章是刚刚发表在Plos Biology上关于家蚕幼虫取食策略，作者来自东京农业科技大学。

许多草食性昆虫是单食的或寡食的，它们已经进化为选择有限范围内的寄主植物。他们利用灵敏的味觉来识别寄主植物。植物次生代谢产物和糖被认为是使昆虫能够识别寄主植物并评估其作为食物质量的关键化学线索。然而，对宿主植物识别的神经元和行为机制了解甚少。本文作者研究了家蚕(Bombyx mori) 的幼虫中的两步寄主接受系统。第一步是由化学感觉器官下鄂须（MP）控制。在拍打叶边缘期间，MP会检测到叶表面化合物含量，从而识别宿主植物但不会马上咬住。 MP中的化学感觉神经元对绿原酸（CGA），槲皮素糖苷和β-谷甾醇（βsito）具有超高灵敏度。仅当检测到这3种化合物时，幼虫才会进行撕咬测试，第二步对其进行评估。另一种化学感觉器官是位于外颚叶（MG）中的低敏感性神经元主要检测被咬伤渗出的叶汁中的蔗糖，使幼虫接受叶片并进行持续咬伤（进食）。本文报道的两步宿主接受系统可能是许多植物性昆虫取食行为的基础，并确定了它们的进食习惯。

Two peripheral chemosensory organs control two-step biting behaviors in the silkworm

当家蚕碰到叶子时，首先会使用外周的化学感应器官（下颚）拍打叶片，然后间歇性地撕咬叶片边缘几次，最后进行连续咬合（每秒2-3次）伴随着头部沿叶片边缘沿腹侧方向摇动。 拍打式的间歇性咬合被认为是测试撕咬，而伴随头部移动的连续咬合为持久撕咬。

下鄂须（MP）和外颚叶（MG）的移除则会导致持续性撕咬消失。

Fig 1. MP and MG are responsible for test and persistent biting. (A) Feeding on mulberry leaves by silkworm larvae. (1) Palpation: a silkworm larva first palpates the leaf surface with its maxilla (MP and MG) for 5–30 seconds. The white arrow and arrowhead indicate MP and MG. (2) Test biting: the larva bites the leaf edge several times intermittently during palpation. (3) Persistent biting: the larva nibbles the leaf edge repeatedly (2–3 times per second) with its head moving in the dorsoventral direction along the leaf edge. Magenta arrows indicate the direction of head movement. (B) Mouthparts of a silkworm larva. Upper larval mouthparts including 1 pair of maxilla. Lower higher-magnification view of the maxilla. The maxilla consists of the MG and MP. The MG has 2 gustatory sensilla, the LS and MS. (C) Frequency of biting by intact, MP-ablated, MG-ablated, and AN-ablated larvae of mulberry leaves over a 10-second period. Data are means Å} SD (n = 5). For numerical raw data, please see S2 Data. (D) Representative raster plots of the timing and duration of the biting behavior of larvae in (C). Red and green lines indicate test and persistent bites, respectively. AN, antenna; LS, lateral styloconic sensillum; MG, maxillary galea; MP, maxillary palp; MS, medial styloconic sensillum.

MP recognizes edible leaves by sensing leaf-surface compounds and induces test biting

• These results suggest that silkworm larvae select their diet sequentially at 2 points, before test and persistent biting, and that host-plant recognition is largely completed when they make a first bite.

Test biting requires a set of host-plant compounds detected by ultrasensitive MP sensory neurons

• a trace amount of the set of CGA + ISQ/Q3R + βsito contribute to host recognition and induction of test biting.

Sucrose and myo-inositol induce persistent biting via MG and modulate the amount of food intake

• sucrose and myoinositol contribute to induction of persistent biting by stimulating MG.