Towards an attract-and-kill strategy for sustainable tick control: combined effects of Metarhizium anisopliae and phytochemical attractants from Senna didymobotrya against Amblyomma variegatum and Rhipicephalus appendiculatus.

Amblyomma variegatum and Rhipicephalus appendiculatus are ticks of veterinary and zoonotic importance in sub-Saharan Africa. Presently, their control mainly relies on synthetic acaricides, which are limited by resistance and environmental harm. Sustainable alternatives, such as combining tick attractants with entomopathogenic fungi in attract-and-kill strategies, are therefore needed. This study aimed to determine (i) the effect of attractants from Senna didymobotrya (methanol extract of S. didymobotrya flowers, squalene, linoleic acid, and squalene: linoleic acid (1:1) blend) on Metarhizium anisopliae ICIPE 7 germination and virulence; (ii) adhesion and horizontal transmission of ICIPE 7 among ticks; and (iii) tick behavioural responses to the most compatible attractant. Throughout the study, methanol extract and squalene maintained the highest overall mean germination (> 90%), while the blend and linoleic acid slightly reduced it (> 80%). The 10% squalene: linoleic acid (1: 1) blend formulated with ICIPE 7 was the most consistently effective treatment against both A. variegatum and R. appendiculatus. Both tick species retained more conidia at 0 h, but R. appendiculatus adhesion declined significantly over 72 h (p < 0.0001). Horizontal transmission of ICIPE 7 was confirmed, causing 100% mortality in A. variegatum recipients and lower mortality in R. appendiculatus recipients. Semi-field assays demonstrated that most ticks were attracted from 1 m, with dry ice, attraction-aggregation-attachment pheromone, and both undiluted and diluted (1 mg/mL) squalene: linoleic acid (1: 1) blends showing similar efficacy. These results support the potential use of M. anisopliae ICIPE 7 combined with squalene: linoleic acid blend in attract-and-kill devices for sustainable tick management.