Abstract
The olfactory system of insects is essential in many crucial behaviors, such as host seeking, mate recognition, and locating oviposition sites. Lepidopteran moths possess two main olfactory organs, including antennae and labial palps. Compared to antennae, the labial palps are relatively specific and worthy of further investigation due to the labial-palp pit organ (LPO), which contains a large number of sensilla located on the tip segment. The fall armyworm, Spodoptera frugiperda, is a worldwide lepidopteran pest, which can damage more than 350 plants and cause significant economic losses. In this study, we surveyed the structure of the labial palps and LPO of S. frugiperda using a super-high magnification lens zoom 3D microscope. Then, the distribution and fine structure of sensilla located in the LPO of S. frugiperda were investigated using scanning electron microscopy. Subsequently, the electrophysiological responses of labial palps to CO2 and 29 plant volatiles were recorded by using electrolabialpalpography. Our results showed the fine structure of labial palps, the LPO, and the sensilla located in the LPO of S. frugiperda. Moreover, we demonstrated that the labial palps are olfactory organs that respond to both CO2 and other volatile compounds. Our work established a foundation for further study of the roles of labial palps in insect olfactory related behaviors. Further investigations on the function of labial palps and their biological roles together with CO2 and volatile compound responses in S. frugiperda are necessary, as they may provide better insect behavioral regulators for controlling this pest.
Highlights
The sophisticated olfactory sensing organs of most insects have important roles in detecting host volatiles, recognizing mates, and locating oviposition sites
The results indicated that there are two types of sensory neurons in the labial-palp pit organ (LPO) of S. frugiperda, one of which could be strongly activated by different concentrations of CO2, while the other type showed no response to CO2
In an effort to research the function of another crucial olfactory organ, the labial palp, the fine structure of LPO and LPO sensilla in S. frugiperda were investigated in detailed in the present study
Summary
The sophisticated olfactory sensing organs of most insects have important roles in detecting host volatiles, recognizing mates, and locating oviposition sites. These organs are mainly distributed in the head, including antennae and mouthpart appendages. As the primary olfactory sensory organs, insect antennae bear abundant of sensilla that are sensitive to plant volatiles, Labial Palps of Spodoptera frugiperda sex pheromones, and other volatile components. Some olfactory sensilla are found on mouthpart appendages, such as maxillary palps (Syed and Leal, 2007; Bohbot et al, 2014) and labial palps (Stange and Stowe, 1999; Galizia and Rossler, 2010). As an important sensory organ, the well-developed labial palps are located on each side of the proboscis in adult Lepidoptera. The labial-palp pit organ (LPO) is a unique structure of lepidopteran species that is located on the apex of labial palps, within which the sensilla lie
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