Threshold-dependent improvement in sex separation efficiency by NaCl pretreatment of larval–pupal mixtures in mass-reared Aedes albopictus

Exposure of larval–pupal mixtures to 15% NaCl for 60 min led to 100% larval mortality via osmotic imbalance and intestinal tissue damage, while pupae remained unaffected due to their impermeable cuticle. Males emerging from treated pupae exhibited comparable emergence, longevity, and flight ability to controls, indicating no adverse effect on male quality. NaCl pretreatment significantly improved sorting efficiency and reduced female contamination in manual sorting, achieving a 3.9-fold reduction in adult-stage contamination. Although automatic sorters increased throughput, reductions in female contamination were not statistically significant. Importantly, the sorting benefits of NaCl treatment were threshold-dependent and most evident at larger processing scales. NaCl pretreatment is a simple, scalable, and biologically safe strategy to enhance sex separation in Ae. albopictus mass production. It is particularly advantageous under high-throughput conditions and preserves male fitness, supporting the stringent quality standards required for successful SIT-based mosquito control.