Eco-friendly solutions for Dactylopius opuntiae (Cockerell) (Hemiptera : Dactylopiidae) control using plant extracts and entomopathogenic fungi

The management of Dactylopius opuntiae (Cockerell), a major cactus pest, has relied on chemical insecticides, raising environmental concerns. This study assessed the efficacy of plant extracts (Ricinus communis, Capsicum annuum, and Nicotiana glauca) and fungi (Alternaria murispora and Alternaria destruens) alone and in combination at 25%, 50%, and 100% of the recommended field concentrations. Twenty-day-old young female D. opuntiae were treated topically on Opuntia ficus-indica cladodes under controlled conditions (25 ± 1°C, 66 ± 5% RH, 16:8 h light/dark) for 10 days. Plant extracts showed minimal effects in conidial germination of A. murispora (0.50% to 2.92%) and A. destruens (1.92% to 3.43%), indicating compatibility. At 25% concentration, the highest mortalities were observed with N. glauca + A. murispora (59.3%) and N. glauca + A. destruens (56.7%). At 50% concentration, N. glauca + A. destruens (61.3%), N. glauca + A. murispora (65.3%), and N. glauca alone (67.3%) showed the highest mortality rates. At 100% concentration, the highest mortalities were found with N. glauca + A. murispora (83.3%) and N. glauca + A. destruens (78.7%). The treatment N. glauca + A. destruens showed the lowest median survival time (MST) of 6.0 days at 100% concentration, which increased to 10.0 days at 50% and 25% doses. The treatment N. glauca + A. murispora showed the lowest LC₅₀ value (1.8 × 10⁷ conidia mL−1). Combining N. glauca with A. murispora and A. destruens enhanced efficacy against D. opuntiae.