Abstract: 【Aim】The aim of this study is to investigate the role of the important inhibitory neurotransmitter γ-aminobutyric acid (GABA) B-type (GABA_B) receptor in modulating the feeding preference of the fall armyworm, Spodoptera frugiperda larvae in response to sweet and bitter substances. 【Methods】 RT-qPCR was used to identify the expression levels of GABA_B receptor gene in larvae (day-2 1st instar to day-2 6th instar) and different tissues (head, cuticle, midgut, fat body and hemolymph) of the day-2 5th instar larvae of S. frugiperda. The GABA_B receptor gene was silenced by feeding the 5th instar larvae of S. frugiperda with dsGABA_B R. The GABA_B receptor antagonist was injected into the 5th instar larvae. Using the leaf disc method, the feeding preference indexes for sucrose (sweet substance) and sinigrin (bitter substance), as well as the feeding area on maize leaves of the 5th instar larvae after the treatments with dsGABA_B R and GABA_B receptor antagonist were detected, respectively. 【Results】The expression level of GABA_B receptor gene in the 1st instar larvae was significant higher than those in the other instar larvae of S. frugiperda. The expression level of GABA_B receptor gene in the fat body of the 5th instar larvae of S. frugiperda was significantly higher than those in the other tissues. After dsGABA_B R feeding treatment, the feeding area on maize leaves of the 5th instar larvae significantly decreased as compared with that of the control larvae, the 5th instar larvae didn’t significantly prefer to feed sucrose and exhibited aversive feeding behaviors to the bitter substance sinigrin. After injecting GABA_B receptor antagonist into the hemolymph, the feeding area on maize leaves of the 5th instar larvae also decreased significantly as compared to that of the control larvae. Unlike the control larva significantly preferred to feed sucrose, the 5th instar larvae injected with GABA_B receptor antagonist showed obviously aversive feeding behaviors to sucrose. While both control larvae and larvae injected with GABA_B receptor antagonist exhibited aversive feeding behaviors to the bitter substance sinigrin. 【Conclusion】 GABA_B receptor could not only affect the food ingestion amount of S. frugiperda larvae, but also could change the preference tendency to sweet substances. While the aversive feeding behaviors for bitter sinigrin were not significantly changed by GABA_B receptor. Our results contribute to understanding the regulation mechanisms of feeding behaviors in insects.

Key words: Spodoptera frugiperda, GABA_B receptor, RNAi, antagonist, food consumption amount, feeding preference