Table 1 Vector competence traits measured in I. scapularis and I. pacificus

Host attachment success

Successful attachment to a competent host, typically a small mammal, is necessary for potential pathogen acquisition [110]

I. pacificus had significantly higher host attachment success than I. scapularis

Feeding rate

Longer attachment to hosts can facilitate pathogen transmission, but may also stimulate host immune responses [111,112,113]

I. scapularis fed to repletion significantly faster than I. pacificus

Engorgement weight

Higher engorgement weights may reflect higher resource uptake and be associated with greater molting success and/or survivorship [76] but see [59]

I. pacificus had significantly higher engorgement weights than I. scapularis

Molting success

Successful larval molting is a prerequisite for pathogen transmission during the nymphal life stage [110]. Transstadial transmission is also required but has previously been measured at high rates for both I. scapularis [114, 115]

An equal proportion of I. scapularis and I. pacificus successfully molted

Pathogen acquisition (host to tick)

As B. burgdorferi is not vertically transmitted, pathogen acquisition by larvae is crucial for B. burgdorferi maintenance and amplification [12]

An equal proportion of I. scapularis and I. pacificus acquired their respective sympatric pathogen strain, and an equal but lower proportion of I. scapularis and I. pacificus acquired their allopatric pathogen strain

Pathogen transmission (tick to host)

As the adult vector life stages typically feed on non-competent reservoir hosts, efficient pathogen transmission by nymphs to hosts is critical for B. burgdorferi maintenance and amplification [12]

I. scapularis transmitted the pathogen to a greater number of hosts than I. pacificus which did not transmit to any hosts, although unequal numbers of infected ticks were applied to hosts