Attract-and-kill strategy for sustainable control of ticks Using entomopathogenic fungus, metarhizium anisopliae and extracts of senna didymobotrya

Abstract

The increasing prevalence of acaricide resistance and the expanding range of invasive tick species necessitate the use of alternative interventions, such as semiochemicals and biopesticides, for sustainable tick control. The current study employed an olfactory-based bioassay-guided approach to screen and identify tick attractants in methanol leaf, flower, seedpod and twig branches extracts of Senna didymobotrya, a plant that has been established to alter the behaviour of ticks. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was conducted to characterize the chemical composition of the extracts and fractions. In addition, the effect of various concentrations of the identified attractants on the viability and virulence of Metarhizium anisopliae ICIPE 7, a potent tick biopesticide, was assessed by exposure of the fungus to headspace volatiles of the attractants and immersion tests, respectively. Floral extracts elicited the highest attraction to Amblyomma variegatum (P< 0.001) and Rhipicephalus appendiculatus (P = 0.060) adults. Fractionation of the floral extract using solvents of increasing polarity revealed that hexane and ethyl acetate fractions were most attractive to A. variegatum (P< 0.001) and R. appendiculatus (P< 0.001) respectively. However, the hexane fraction also attracted R. appendiculatus (P = 0.040). Chemical analysis of the active extract and fractions, combined with a literature search, identified squalene and linoleic acid as potential attractants. Attraction bioassays conducted with these two compounds and their blend (1:1) demonstrated that A. variegatum (P< 0.010) and R. appendiculatus (P< 0.001) were significantly attracted to the two-component blend. The crude floral extract and squalene did not affect the viability of M. anisopliae ICIPE 7. Linoleic acid, squalene: linoleic acid blend (1:1) and the attraction aggregation attachment pheromone (AAAP) negatively affected the viability of ICIPE 7. Squalene: linoleic acid (1:1) (10%) combined with ICIPE 7 resulted in the shortest lethal time response to mortality of 50% of the tick population (LT50) in both A. variegatum and R. appendiculatus (9.05 and 10.3 days, respectively). These findings suggest that the (10%) squalene: linoleic acid blend (1:1) can be combined with M. anisopliae ICIPE 7 for the sustainable control of A. variegatum and R. appendiculatus populations in an "attract-and-kill" strategy leading to control of ticks and tick-borne diseases