The company said the change is 'temporary' and being made 'so we can provide a more reliable service.'
A spokesman added: "As is the case with other transport operators and many other organisations, we are seeing a continuing impact on our staffing levels as a result of the pandemic.
"We therefore looked at the Northamptonshire bus network to find routes where a temporary service reduction could be made and impact the smallest number of passengers. Out of 45 services in Northamptonshire we are making frequency changes to four of them.
"We recognise that the disruption to services we have seen over the past few weeks is unsettling and inconvenient for customers and therefore reducing services in some places should mean that we are able to provide services more reliably.”
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Other changes are being made to a few routes between Corby, Kettering, Wellingborough, Rushden and Higham Ferrers.
Buses on route 2 between Kettering and Corby Business Academy will run up to every 60 minutes instead of half-hourly Mondays-to-Fridays from next week.
Stagecoach has had to cancel up to 80 journeys a day across its Northamptonshire network for the last four months through a shortage of drivers.
That has been blamed on staff being forced to self-isolate by Covid regulations and also a national crisis over the number of HGV drivers.
Many bus drivers are reported to have quit to take higher-paid agency work while recruitment has been hampered by hold-ups issuing licences at the DVLA.