Isolation and laboratory evaluation of two strains of Aspergillus for controlling Haemaphysalis longicornis (Acari: Ixodidae)

Abstract

Abstract Haemaphysalis longicornis (Acari: Ixodidae) is an important vector tick that can transmit a number of pathogens to humans and domestic animals worldwide. Entomopathogenic fungi have been substantiated to be effective in controlling ticks. However, a limited number of studies have assessed the use of ubiquitous Aspergillus spp. strains for the control of H. longicornis. In this study, we isolated Chinese native A. flavus and A. niger strains and evaluated their pathogenicity on different life stages of H. longicornis in the laboratory. Batches of unfed larvae, unfed nymphs and unfed female adults of H. longicornis (i.e., n = 20 for each stage) were immersed in 0.05% tween 80 suspensions of each A. fungus (1×105, 1×106, and 1×107 conidia/mL), whilst control groups for each stage were exposed only to sterile distilled water plus 0.05% Tween 80. All bioassays consisted of four groups of ticks (three experimental and one control group). Ticks were observed daily until 100% mortality was recorded in all treatment groups. Twelve days after treatment, A. flavus and A. niger strain resulted in 100% mortality of unfed tick larvae at all concentrations. Based on the calculated LC50 (median lethal concentration ) values, it was revealed that A. flavus was more pathogenic than A. niger. However, there was zero mortality and no mycelium growth in the nymph and adult female tick groups at all exposure times when using different conidial concentrations. Our results demonstrated that two native Chinese Aspergillus spp. strains showed high entomopathogenicity in the lab condition, representing a possible promising natural product to be used in alternative or in combination to other acaricidal compounds currently used for controlling the H. longicornis, although further field studies are needed to determine the best route and frequency of application for using these fungi as a bio-control agent against ticks.