Kaolin particle film repellent effect against the wild cochineal Dactylopius opuntiae and its impact on cactus pear health

Opuntia ficus-indica (L.), a cactus, a critical crop in Morocco, has been severely damaged by Dactylopius opuntiae since its introduction in 2014. This study evaluated the insecticidal and preventive effects of kaolin clay against D. opuntiae females and nymphs under laboratory and field conditions and assessed its impact on the physiological parameters of health and wettability of cactus cladodes. Laboratory cage experiments revealed that Kaolin-treated cladodes (30 g/L) had significantly fewer colonies (3.67) than water-treated controls (7.33) after 42 days, with stable evolution up to 60 days. Choice tests showed more nymphs on untreated cladodes (7) than on treated ones (3) after one day. No-choice tests revealed significantly higher nymph mortality on kaolin-treated cladodes (75 dead nymphs) compared to controls (21) by day 44. Field trials supported these findings, with treated cladodes showing only 16 colonies after 40 days compared to 35 on untreated ones. Kaolin also induced direct insecticidal activity, causing 62% and 74% nymph mortality three days after application at 30 g/L and 60 g/L, respectively. Female mortality reached 32% after five days at the double dose. In addition, Kaolin preserved greener cladodes with darker tissues, and higher chlorophyll levels, while infested cladodes showed chlorophyll loss and lighter color. Kaolin also transformed cladode surfaces from hydrophobic (contact angle: 111.11°) to hydrophilic (contact angle: 67°) after one day, with a decrease to 57° after 21 days. These results highlight the potential of Kaolin as a preventive control without affecting cactus quality.