Food attractants for field population monitoring of Spodoptera exigua (Hübner)

Spodoptera exigua (Hubner) is an important agricultural pest with worldwide distribution. Monitoring the population dynamics of adults and predicting the occurrence of next generation are the basis of prevention and control. Insect attractants are based on preferences for foods or their volatiles and have great potential for pest monitoring and management. To evaluate the monitoring success of food attractants on S. exigua populations in the field, we first quantitatively analyzed the reproductive organ development of adults in a laboratory population. The ovarian development of females was divided into four stages. The length range of the testis major axis of males at different ages was established according to the principle of testis development. This allowed documentation of the reproductive status of adults trapped in the field. In 2019 and 2020, we used food attractant trapping combined with reproductive system examination to monitor the population dynamics and reproductive development of S. exigua adults in natural environment. The results showed obvious generational changes in the population density dynamics of males and females of S. exigua. During the two-year monitoring period, the ovarian development level and mating times of trapped females in the second generation increased at first and then decreased with time. The number of eggs within ovarioles trapped initially decreased and then increased over time. The ovarian development level and mating times of trapped females in the third-generation adults increased gradually over time, and the number of eggs in female ovarioles decreased gradually over time. The age of trapped males in the second generation initially increased and then decreased over time. The age of males in the third generation increased gradually over time. There were significant differences in the reproductive development of female and male moths trapped in different generations in 2019. This study showed that trapping using food attractants can monitor field population dynamics of S. exigua. Combined with examination of reproductive system anatomy, it can monitor the reproductive organ development, mating, and oviposition status of wild adults.