Insecticidal, repellent, and histopathological effects of selected botanical extracts on the rice leaf folder (Cnaphalocrocis medinalis)

The rice leaf folder (Cnaphalocrocis medinalis) is a key pest in Asian rice fields that causes significant yield loss. This study evaluated the insecticidal potential of 10 methanolic botanical extracts from Azadirachta indica, Calotropis sp., Ricinus communis, Justicia adhatoda, Aristolochia bracteolate, Cassia auriculata, Acorus calamus, Nicotiana tabacum, Pongamia pinnata, and Lawsonia inermis. The extracts were tested at concentrations of 1 %, 3 %, 5 %, 10 %, 15 % under laboratory conditions. Larval mortality was recorded at 24, 48, and 72 h and repellency was assessed using the filter paper disc method. Histopathological changes were examined in thoracic muscles, gastrointestinal tracts, and Malpighian tubules. The overall findings demonstrated that A. indica and J. adhatoda consistently caused the most larval mortality across all concentrations and time intervals, with one-way ANOVA indicating highly significant effects at 24, 48, and 72 h (p < 0.001). Probit analysis established lethal concentration values with an LC50 value of 28.5 ppm for A. indica, which is consistent with the previously reported efficacy of neem-based botanicals against rice leaf folder larvae. A. indica and P. pinnata showed 100 % repellent activity while C. auriculata and L. inermis were the least effective (<30%). A. indica extracts caused intense histopathological effects resulting in significant tissue alterations with an H-score ranging from 255 to 285 while a lower H-score was recorded for the control. Overall, the selected botanical extracts caused significant larval mortality and pronounced histopathological alterations in C. medinalis larvae.