›› 2015, Vol. 58 ›› Issue (3): 223-236.

• RESEARCH PAPERS •     Next Articles

Antennal lobe neurons of Spodoptera litura (Lepidoptera: Noctuidae) and their responses to plant odors and sex pheromones

WAN Xin-Long1, LI Jiang-Hui1, LAO Chong2, DU Yong-Jun1,*   

  1.  (1. Institute of Health and Environmental Ecology, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China; 2. Cixi Station of Forestry Pest Control, Cixi, Zhejiang 315300, China)
  • Online:2015-03-20 Published:2015-03-20

Abstract: 【Aim】 This study aims to understand the structure of the antennal lobe (AL) of the tobacco cutworm, Spodoptera litura and its neuronal activities in response to plant volatiles and sex pheromones. 【Methods】 The structure of the antennal lobe of S. litura adults was scanned and observed by using the confocal laser scanning. The neuronal activities of AL were recorded and analyzed through multi-unit recording (MR) method when the antennae were stimulated by six plant-derived volatile compounds including benzaldehyde, benzyl alcohol, phenylacetaldehyde (PAA), 2-hydroxybenzaldehyde, cis-3-hexenyl acetate, and  trans-2-hexenal, and sex pheromones including (Z,E)-9,11-tetradecadienyl acetate (Z9E11-14:Ac) and (Z,E)-9,12-tetradecadienyl acetate (Z9E12-14:Ac), respectively. Wind tunnel was employed as the bioassay tool to test the behavioral responses of S. litura adults to the stimulants in order to confirm the neuronal activities shown in the MR experiments. 【Results】 The ALs in the brain of S. litura adults identified in the confocal laser scanning were composed of 67 and 66 glomeruli in males and females, respectively. As reported in previous studies, a macroglomerular complex (MGC) dealing with pheromone information, was only found in the AL of male adults. The total and average volumes of glomeruli in female adults were higher than those in male adults. The MR results showed three spontaneous discharge patterns of neurons, i.e. diffuse spiking (irregular frequency), moderate spiking (slower and broader distributional frequency), and fast spiking (bursting high frequency). Three types of neuron responses to odor stimulation were present in all recordings, i.e., excitatory, inhibitory, and unresponsive. The response types (excitatory, inhibitory or no response) in the AL neurons were found to be dependent on the chemical structure of stimulants and their concentrations. The AL neurons of female adults had weak response to sex pheromones and single component of the tested plant volatiles, while those of male adults showed strong excitatory responses to sex pheromones Z9E11-14:Ac and Z9E12-14:Ac, benzaldehyde, benzyl alcohol, and PAA, suggesting the effect of aromatic compounds. The wind tunnel tests indicated that the majority of male adults significantly chose to stay on sex pheromones and aromatic compounds, and this was consistent with the MR results. 【Conclusion】 The relationship between the neuronal responses of female adults of S. litura and the concentrations of all stimuli is different, depending on different neurons or stimulus chemicals. The neuronal activities of male adults are positively correlated to the concentrations of sex pheromones within the tested range, but show no significant differences among the tested concentrations of the plant odors except for cis-3-hexenyl acetate.

Key words: Spodoptera litura, antennal lobe, neurons, multi-unit recording, plant odors, sex pheromone, glomerulus, wind tunnel