Assessment of the Residual Toxicity of the Insecticides on the Egg Parasitoid Trichogramma chilonis of Spodoptera liturain Sunflower under Elevated CO2 and Temperature Conditions

Abstract

This study assessed the residual toxicity of Spinosad, Emamectin benzoate, Thiodicarb, Monocrotophos and Fenvalerate to the egg parasitoid Trichogramma chilonis on sunflower under elevated carbon dioxide (eCO2) and elevated temperature (eTemp) conditions. Sunflower plants were maintained in controlled-temperature and growth chambers under ambient CO2 (380 ± 25 ppm; 28°C), eCO2 (550 ± 25 ppm; 28°C), elevated temperatures of 29, 31, 33 and 35 ± 1°C, and combined eCO2 and elevated temperature treatments. Insecticides were applied at LC50 and field-recommended concentrations (FRC), and parasitised egg cards were exposed to treated leaves at 0, 3, 6, 9, 12, 15 and 18 days after spraying. Adult emergence was recorded after 24 h. Adult emergence was lowest immediately after spraying and increased with time, indicating a progressive decline in residual toxicity. Elevated CO2 reduced mean adult emergence relative to ambient CO2, while increasing temperature from 29°C to 35°C reduced emergence at both concentrations. The combined eCO2 and eTemp treatments further reduced emergence relative to elevated temperature alone. Among the insecticides, Emamectin benzoate consistently produced the highest adult emergence and was comparatively safer to T. chilonis, followed by thiodicarb, spinosad and monocrotophos. Fenvalerate produced the lowest emergence and was comparatively more harmful. The findings indicate that elevated CO2 and temperature can modify insecticide compatibility with T. chilonis and should be considered when integrating chemical and biological control.