Effects of temperature, relative humidity, and photoperiod on life history of <i>Cotesia ruficrus</i> (Hymenoptera: Braconidae), an indigenous parasitoid of <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae)

The indigenous parasitoid Cotesia ruficrus (Haliday) (Hymenoptera: Braconidae) shows promise as a biological control agent for managing the invasive fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in China. However, the influence of environmental factors on C. ruficrus performance remains poorly understood. This study aimed to investigate the effects of temperature, relative humidity, and photoperiod on the life history of C. ruficrus. The life-history traits were measured at 5 different temperatures (20, 23, 26, 29, and 32 ± 1 °C), 4 RH levels (40%, 55%, 70%, and 85 ± 5%), and 5 photoperiod levels (L:D 8:16, 10:14, 12:12, 14:10, and 16:8). As temperature increased from 20 to 32 °C, the immature developmental duration (from 19.8 to 11.0 d), egg load (from 263.8 to 100.8), adult size (from 0.75 and 0.72 to 0.66 and 0.65 mm for female and male, respectively), and longevity (from 28.43 and 24.98 to 5.03 and 5.3 d for female and male, respectively) significantly reduced, while parasitism rates remained stable (56.8% to 66.3%) but emergence rates decreased above 26 °C (from 93% to 75%). Higher RH (>70%) improved emergence rates (87% to 93%), sex ratios (0.63), egg load (278), and longevity (above 10 d for male and 14 d for female), with no significant effect on parasitism rates (65% to 69%). The highest parasitism rate (65%), sex ratio (0.63), and egg load (278) occurred under 14:10 photoperiod, with emergence rates (81% to 87%) unaffected by photoperiod changes. Collectively, optimal conditions for C. ruficrus development and reproduction were identified as 26 ± 1 °C temperature, 14:10 photoperiod, and above 70% RH.