Assembly behaviour by the lone star tick, Amblyomma americanum (Acari: Ixodidae), to tick excreta is not species-specific and influenced by relative humidity

Abstract

This study tested the lone star tick, Amblyomma americanum, vector of ehrlichiosis, tularemia, Southern tick-associated rash illness borreliosis, for arrestment to excreta from different tick species. The purpose was to explore off-host clustering along with spread and establishment into habitats occupied previously by other ticks. This response was analysed in relation to relative humidity since this is environmental. Females had the greatest responses towards natural excreta, and excreta components guanine and uric, and nymphs behaved like adults but with lower response levels. Response was poor by larvae, by showing inconsistent, or no response to excreta exposure. Clustering occurred on excreta from Amblyomma maculatum, Dermacentor variabilis, Ixodes scapularis, and Rhipicephalus sanguineus. This indicates there is unlikely a species-specific assembly component in excreta of A. americanum. In fact, highest level of assembly by A. americanum was to I. scapularis excreta. Greater speed and intensity for assembly occurred at 33% RH, with more ticks engaged in clustering on excreta-coated surfaces, than at 93% RH. No avoidance reaction was observed when exposed to other tick species excreta, suggesting that excreta from heterospecifics do not repel A. americanum. We conclude that dehydrating conditions cause lone star ticks to more actively pursue optimal moisture-rich, favourable habitats signalled by tick excreta. This behaviour is more important for females and nymphs than larvae, and there is capacity to recognize excreta of overlapping tick species. This co-recognition could facilitate occurrence of A. americanum with other ticks such as I. scapularis that are frequently sympatric with A. americanum through much of their geographic distribution.