Eco-Physiological Response of the Egg Parasitoid Trichogramma evanescens (Hymenoptera: Trichogrammatidae) to Varying Light Intensities under Hyper-Arid Solar Kinetics

Egg parasitoids of the genus Trichogramma are widely utilized inundative biological control agents, yet their field efficacy in hyper-arid regions is strictly bottlenecked by abiotic constraints. This study evaluated the effects of four light intensities (0, 500, 1000, and 2000 Lux) on the parasitism rate, emergence rate, progeny sex ratio, and adult longevity of Trichogramma evanescens under controlled conditions (27 ± 1ºC, 60 ± 5 % RH). To bridge laboratory outcomes with field practicalities, a Beer-Lambert canopy light extinction model was integrated with the diurnal solar radiation kinetics of Basrah, Iraq (5.94 kWh/m2 day, peaking at 740 W/m2). Laboratory bioassays revealed optimal performance at 500 Lux, yielding a mean parasitism rate of 85.4 % (95 % CI: 82.1 - 88.3 %) and a female-biased sex ratio of 68.5 % (95 % CI: 64.1-72.6 %), which was statistically comparable to 1000 Lux. Complete darkness (0 Lux) significantly impaired parasitism to 52.1 % (95 % CI: 47.3 -56.8 %). Exposure to 2000 Lux (simulating unshaded midday conditions) severely reduced adult longevity to 4.1 days (95 % CI: 3.5 - 4.7 days) and caused a male-biased inversion (28.9% females; 95 % CI: 22.1- 35.7 %). Canopy light-penetration modeling predicted that dense frond layers (LAI ≥ 2.0) buffer extreme midday radiation, maintaining parasitism efficacy above 60%. These predictions were empirically confirmed in a field release trial conducted in a commercial date palm orchard in Basrah, where early-morning releases into middle and inner canopy strata achieved field parasitism rates of 81.4% and 76.2%, respectively, compared to only 18.4% under unshaded solar-noon exposure (R²field = 0.912; RMSE = 8.84%). These findings establish a quantitative, field-validated framework for timing field releases during low-radiation diurnal windows in high exposure agroecosystems.