Effects of Saturated Soil Moisture on Pupal Development Regarding Fall Armyworm

Spodoptera frugiperda, known as fall armyworm (FAW) which is a major pest of corn, is spreading rapidly all over the world as an invasive pest. Similar to other Lepidoptera insects, the FAW pupae usually develop in soil. Therefore, the soil moisture would be an important factor that impacts their growth. In order to study the development and eclosion of FAW pupae under 100% soil moisture environment, three factors were selected for experiments in this study. These factors were: duration of 100% soil moisture (0h, 24h, 48h, 72h), initial soil moisture before larvae entering soil (0, 50%), and pupal ages (1-day, 4-day, 7-day). We have discovered that: 1. The FAW pupae eclosion rate decreased with the increase of 100% soil moisture duration, and after 72 hours of continuous treatment, the eclosion rate decreased to 0. 2. The younger pupae age of FAW, the more susceptible it would be affected by 100% soil moisture, and the eclosion rate of 7-day-old pupaday-old pupae is higher than the 1-day-old pupaday-old pupae. 3. FAW pupae entered in dry soil (moisture 0) have a higher survival rate under 100% soil moisture stress, and their eclosion rate is higher than the pupae entered in wet soil (moisture 50%). Our study showed that when FAW pupae were exposed to soil moisture stress, the three factors of excessive stress time, wet soil entering moisture (50%), and younger pupal age all had a significant negative impact on their development. Analysis of the FAW pupal response to 100% soil moisture provides a valuable addition to the pupal ecology regarding soil moisture response of lepidopterans. In practice, an understanding of irrigation patterns and soil moisture control in maize cultivation will facilitate the practical application of integrated pest management strategies in FAW control.