Unveiling the Biocidal Effect of Giant Milkweed, Calotropis gigantea (L.) W.T. Aiton On the Cassava Mealybug, Phenacoccus manihoti Matile-Ferrero

Cassava (Manihot esculenta Crantz) (Euphorbiaceae) is a critical staple crop in tropical and subtropical regions that contributes substantially to food security and rural livelihoods. However, its productivity is increasingly threatened by the cassava mealybug, Phenacoccus manihoti Matile-Ferrero, a significant pest of cassava, causing extensive crop losses globally. Although conventional chemical pesticides are effective, they pose risks to ecosystems and human health, necessitating alternative control methods. This study explores the potential of Calotropis gigantea (L.) W.T. Aiton, belonging to the family Asclepiadaceae, a medicinally significant plant, as a botanical insecticide against P. manihoti. The toxicity of the crude ethyl acetate extract of C. gigantea leaves and phytol, a key bioactive compound in C. gigantea, was assessed using laboratory assays with topical application methods. The results showed a concentration-dependent efficacy, with an LC50 of 54.68 ppm for the crude extract and 74.41 ppm for phytol at 72 hr after exposure. The ethyl acetate extract exhibited superior toxicity compared to phytol, achieving up to 96.67% mortality at 150 ppm. GC-MS analysis identified 39 bioactive compounds in the extract, with phytol being one of the most prominent compound with insecticidal properties. Formulations (1% EC) of crude extract and phytol were tested, where the crude formulation exhibited a lower LC50 of 54.60 ppm than the phytol formulation (LC50:70.87 ppm). Biosafety studies revealed moderate toxicity of both formulations to the parasitoid Anagyrus lopezi (De Santis) (Hymenoptera: Encyrtidae), but substantially lower than that of conventional insecticides such as thiamethoxam and azadirachtin. These findings demonstrate that C. gigantea is a promising, environmentally safe botanical insecticide that can be effectively used in sustainable pest management strategies, particularly for controlling P. manihoti in cassava.