Effects of Relative Humidity on the Development, Survival, and Reproduction of Paralipsa gularis (Zeller) (Lepidoptera: Pyralidae), a Pest of Stored Grains and Maize

Paralipsa gularis (Zeller) (Lepidoptera: Pyralidae) is a storage pest native to Southeast Asia that has now become a major agricultural pest affecting maize during the late growth stage in the border regions of southern Yunnan, China, adjacent to Southeast Asia. The typical tropical monsoon climate of this region defines distinct rainy and dry seasons with marked differences in ambient humidity; however, the effects of ambient humidity on the growth and development of P. gularis remain unclear. Therefore, we evaluated the effects of five relative humidity (RH) levels on the development, survival, and reproduction of P. gularis under controlled laboratory conditions. The results indicated that RH significantly affected parameters such as the developmental duration of P. gularis at various life stages and the reproductive capacity of adults. Specifically, the response to RH on the developmental duration of P. gularis was stage-specific. Within the range of 45–90% RH, the larval developmental duration gradually shortened, with the shortest duration of 15.48 days observed at 90% RH. The developmental durations of the pupa and adult increased as RH rose. At 90% RH, the developmental durations of the pupa and adult were longest, at 6.68 days and 8.58 days, respectively. The pupation rate and pupal eclosion rate of P. gularis initially increased and then decreased as RH rose, but they did not differ significantly among RH levels. At 75% RH, the pupation rate, pupal eclosion rate, and the weights of fifth-instar larvae and pupae were numerically highest. In addition, unmated females showed the highest observed fecundity at 90% RH. Overall, P. gularis exhibited better developmental status and higher egg-laying capacity in intermediate-to-high RH (75–90%). Our results may help optimize laboratory rearing conditions for P. gularis, provide parameters for future population models, and improve integrated management strategies for this pest.