Effects of Saturated Soil Moisture on Fall Armyworm Pupal Development.

Spodoptera frugiperda, known as the fall armyworm (FAW), a major invasive pest in corn, is rapidly spreading all over the world. Similarly to other Lepidoptera insects, FAW pupae usually develop in soil. Therefore, the soil moisture level is expected to be an important factor impacting their growth. In order to study the development and emergence of FAW pupae in a 100% soil moisture environment, three factors were selected for experiments in this study: the duration of saturated (100%) moisture treatment (0 h, 24 h, 48 h, and 72 h), the initial soil moisture before the larvae entered the soil (0 and 50%), and pupal age (1 day, 4 days, and 7 days). We discovered that (1) the emergence percentage of FAW pupae decreased with an increase in the saturated soil moisture treatment time, and the emergence percentage dropped to 0 after 72 h of continuous treatment; (2) the younger the age of FAW pupae, the more susceptible they were to being affected by saturated soil moisture treatment, and the emergence percentage of 7-day-old pupae was higher than that of 1-day-old pupae; and (3) FAW larvae that pupated in dry soil (0% moisture) had pupae with higher survival rates under subsequent 100% soil moisture stress, whereas those pupating in moderately moist soil (50% moisture) had lower survival rates under the same condition. Our study showed that the initial moisture level of the soil and the length of time the soil is saturated have a significant impact on FAW pupal development. The three factors of excessive stress time, wet initial soil moisture (50%), and lower pupal age ultimately lead to a decrease in the emergence percentage and survival rate of FAW pupae.