What triggers chiggers? Evaluating attraction using chemosensory cues

In the United States, chiggers are considered a nuisance biting pest. However, in many parts of the world, chiggers, such as Leptotrombidium imphalum are vectors for Orientia tsutsugamushi, the causative agent for scrub typhus. Recent studies have found Orientia spp. in the microbiome of North American chiggers, leading scientists to ponder the role, if any, chiggers play in the maintenance of rickettsial agents in the US. Our team focused on trapping and surveillance efficacy. We hypothesized that chiggers use chemosensory cues to orient toward hosts and synthetic attractants could be used to lure them to a source. The goals of this study were: (a) evaluate chigger response to different chemical compounds (b) determine approximate attractant dosage for use in field traps, (c) analyze general chigger behavior and orientation when presented with chemical stimulus. Ultimately, we hope to identify attractants to aid in chigger surveillance and improve overall understanding of chigger behavior. Using a petri dish “arena”, laboratory-reared chiggers were placed in the test arena with a chemical stimulus for 10 minutes. Chigger movements were video recorded and analyzed using insect tracking software. Seven replicates per attractant were conducted for a total of approximately 100 chiggers evaluated per treatment. To determine attraction, video analysis using Adobe After Effects and ToxTrac software will be used. Results of this study will help future researchers and public health across the US better evaluate the role chiggers play in local disease ecology. This study was the first of its kind to evaluate chigger attractants.