植食性昆虫有广食性和专食性之分，这二类昆虫对寄主植物的选择行为截然不同，然而目前对其神经生物学机制了解很少。棉铃虫和烟青虫均属铃夜蛾属昆虫，前者为广食性，寄主包括40余科200余种植物，后者是专食性，寄主仅限于茄科的烟草和辣椒，而嗅觉在二种夜蛾的寄主选择中发挥关键作用。本项目拟在行为、生理和分子三个层面上，由外周到中枢系统解析两种昆虫对寄主植物的产卵选择机制，检验提出的“寄主选择的嗅觉编码”假说，揭示组合编码和标记线路两种模式在寄主选择中的作用。项目将研究两种昆虫的产卵选择行为，阐明相关嗅觉受体神经元的电生理反应特征，用异源表达系统鉴定关键嗅觉受体基因的功能，用活体钙成像探索嗅觉信号在脑嗅觉中心的活性，比较两种昆虫的蕈体大小及学习和记忆能力，利用种间杂交揭示寄主选择行为的遗传规律。研究结果不仅对于阐明昆虫寄主选择行为及其生物学机制具有重要的意义，而且对于寻找害虫防治的新途径具有实用价值。

Host-plant selection by phytophagous insects are different between generalist insects and specialist insects, but their neural coding mechanisms are still unclear. Helicoverpa armigera and Helicoverpa assulta are sibling pest species but have different host-plant ranges. H. armigera is a typical polyphagous species feeding on about 200 plant species in more than 40 families, while H. assulta is an oligophagous species, just feeding on tobacco and hot pepper in Solanaceae. Olfaction plays a vital role in their host-plant selection. In this project, we will use this ideal system to test the hypothesis about olfactory coding patterns of generalist and specialist herbivores we propose. The hypothesis is based on the assumption that neural constraints exist on the amount of information that can be processed and the number and accuracy of decisions that can be made in a given period of time, and generalists encounter more host-associated information/decisions than specialists. Our prediction is that (1) the generalists should largely use the combinational coding pattern to cope with various olfactory cues from many different host-plant species; (2) the specialists should more use the labeled-lines pattern to recognize signature odorants from specific host-plant species; (3) specialists should show greater efficiency and accuracy in host-plant selection; (4) generalists should exhibit greater learning and memory ability and larger volumes of the mushroom bodies in the brain. In order to reveal the olfactory coding mechanisms of the two species from peripheral and central levels, we plan to carry out this comparative study in five aspects: (1) investigating the oviposition-selecting behavior of the two species；(2) characterizing the related olfactory receptor neurons in the antennae and ovipositor; (3) identifying whole sets of olfactory receptor genes expressed in olfactory receptor neurons and analyzing their functions by using heterologous expression systems; (4) examining the neural activities in the central nervous systems of the two species by in vivo calcium imaging; (5) comparing the learning and memory ability of the two species and especially sizes of their mushroom bodies; (6) uncovering the genetic bases of their oviposition-selecting behaviors and physiological features by interspecific hybridization and backcrossing. The results will not only provide insights into olfactory coding mechanisms in phytophagous insects, but also result in new practical methods of insect pest management.