Department of Biological Sciences, Binghamton University, Binghamton, NY 13902, USA.
Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS, Canada, B3H 4R2.
J Exp Biol. 2023 Aug 15;226(16). doi: 10.1242/jeb.245716. Epub 2023 Aug 24.
The parasitic wasp Cotesia congregata suppresses feeding in its host, the caterpillar Manduca sexta, during specific periods of wasp development. We examined both feeding behaviour and the neurophysiology of the mandibular closer muscle in parasitized and unparasitized control M. sexta to determine how the wasp may accomplish this. To test whether the wasps activated a pre-existing host mechanism for feeding cessation, we examined the microstructure of feeding behaviour in caterpillars that stopped feeding due to illness-induced anorexia or an impending moult. These microstructures were compared with that shown by parasitized caterpillars. While there were overall differences between parasitized and unparasitized caterpillars, the groups showed similar progression in feeding microstructure as feeding ended, suggesting a common pattern for terminating a meal. Parasitized caterpillars also consumed less leaf area in 100 bites than control caterpillars at around the same time their feeding microstructure changed. The decline in food consumption was accompanied by fewer spikes per burst and shorter burst durations in chewing muscle electromyograms. Similar extracellular results were obtained from the motorneuron of the mandibular closer muscle. However, chewing was dramatically re-activated in non-feeding parasitized caterpillars if the connectives posterior to the suboesophageal ganglion were severed. The same result was observed in unparasitized caterpillars given the same treatment. Our results suggest that the reduced feeding in parasitized caterpillars is not due to damage to the central pattern generator (CPG) for chewing, motor nerves or chewing muscles, but is more likely to be due to a suppression of chewing CPG activity by ascending or descending inputs.
寄生蜂 Cotesia congregata 在其宿主烟青虫 Manduca sexta 的特定发育时期抑制其取食。我们检查了被寄生和未被寄生的对照烟青虫的取食行为和下颌闭合肌的神经生理学，以确定寄生蜂是如何做到这一点的。为了测试寄生蜂是否激活了宿主原有的停止取食机制，我们检查了由于疾病引起的厌食症或即将蜕皮而停止取食的毛毛虫的取食行为的微观结构。将这些微观结构与被寄生的毛毛虫的微观结构进行了比较。虽然被寄生的和未被寄生的毛毛虫之间存在总体差异，但随着取食的结束，这两组表现出相似的取食微观结构的进展，这表明有一个共同的模式来结束一顿饭。在取食微观结构发生变化的同时，被寄生的毛毛虫在 100 次咀嚼中消耗的叶片面积也比对照毛毛虫少。咀嚼肌肌电图中每个爆发的尖峰数量减少和爆发持续时间缩短伴随着食物消耗的下降。下颌闭合肌运动神经元也得到了类似的细胞外结果。然而，如果切断食道下神经节后面的神经连索，即使在不取食的被寄生的毛毛虫中，咀嚼也会显著重新激活。对接受相同处理的未被寄生的毛毛虫也观察到了同样的结果。我们的结果表明，被寄生的毛毛虫取食减少不是由于咀嚼的中枢模式发生器（CPG）、运动神经或咀嚼肌肉受损，而是更有可能是由于上行或下行输入对咀嚼 CPG 活动的抑制。
