Toxicity of plant extracts against Dactylopius opuntiae under semi-natural conditions

The cactus cochineal, Dactylopius opuntiae (Cockerell, 1929) (Cockerell) (HEMIPTERA: DACTYLOPIIDAE), has continued to expand throughout Morocco since its introduction in 2014, which has resulted in causing severe damage to various Opuntia prickly pear species. The present study provides biological management methods of this insect pest by evaluating the insecticidal effect of Nicotiana glauca Graham and Ricinus communis Linnaeus extracts. The different extraction methods (methanolic, decoction, and maceration) and a positive control D-limonene were used on adult females and nymphs of D. opuntiae. All plant extracts had insecticidal effects and were dependent on concentration and post-treatment evaluation timing. For D-limonene, 100% cactus cochineal mortality was achieved at a concentration of 8%, 24 h post-treatment. The decocted extracts of N. glauca and R. communis and the cold macerated extract of R. communis at a 4% concentration had a mortality rate of up to 70%, 120 h post-treatment. The other three plant extracts (N. glauca/methanol, N. glauca/cold maceration, and R. comminus/methanol) also induced insecticidal activity approaching 70% mortality 120 h post-treatment at a concentration of 8%. Moreover, results of the phytochemical analysis of these extracts indicated high amounts of carotenoids and coumarins. Polyphenol contents ranged from 22.88 ± 0.39 to 68.42 ± 0.50 µg gallic acid equivalent/ mg dried extract, while flavonoid contents ranged from 22.62 ± 5.87 to 131.02 ± 1.46 µg quercetin equivalent/mg dried extract. The lethal dose (LD50) of these extracts reveals that D-limonene was the most toxic with an LD50 = 1019.92 ppm followed by the cold macerated extract of N. glauca with an LD50 = 5860.91 ppm.