Covid-19 isn't the only unwanted visitor New Zealand has seen less of by closing its borders, with biosecurity officials observing a sharp drop in pest incursions.
However, experts say it would take years longer in isolation for the country to see a meaningful blow to invasive pests, which cost our industries more than $1b each year.
Dr David Teulon, director of the agency Better Border Biosecurity, or B3, said disruption caused to the global supply chain appeared to have already reduced the number of plant pests and pathogens entering New Zealand.
Even by March, when the country was just weeks into its pandemic response, the number of notifications around biological risks to plant health and the environment had fallen to 105, compared with 167 in March 2019.
"This is a notable and substantial reduction, particularly as biosecurity was considered an essential service throughout lockdown and our border services were busy throughout looking for unwanted invasive species."
According to the Ministry for Primary Industries biosecurity magazine Surveillance, investigators received 389 plant and environment notifications between January and March - 100 fewer than the same period last year.
By that point, more than 60 countries had reported Covid-19, limiting travel, trade and shipping here and overseas.
Of the 389 notifications, 79 were ruled out as risks, 37 were redirected to other agencies, and 273 were further investigated, including 13 new organisms, most of them plant-associated fungi.
"Covid-19 as a biosecurity event has reminded us and reinforced how critically important it is to protect our border from invasive species," Teulon said.
"Right now, we simply cannot afford to have any new major disruptions from invasive species – similar to PSA or Mycoplasma bovis – because our primary industries will be vital in pulling us through this period of economic disruption and uncertainty."
Dr Craig Phillips, a senior scientist at AgResearch, said it seemed probable the pandemic and border closures will have reduced our risk of new incursions.
"However, I think it would take a years-long border closure – which I certainly hope does not eventuate – to see any real change in pest invasion rates in New Zealand," he said.
"This is partly because it has long been easier to effectively manage biosecurity risks from incoming passengers than from large-scale importations of goods in shipping containers and items like cars and machinery, which will have declined less due to the pandemic.
"Indeed, incoming freight is an area where we most need new technologies to help us keep unwanted pests out of New Zealand."
Imports of plants and plant products were also major risks, he said, but like incoming passengers, more options were available for managing them.
University of Auckland ecologist Associate Professor Margaret Stanley said that, as well as slowing the incursion rate, the pandemic could leave Kiwis with a better understanding of biosecurity.
"Now New Zealanders are familiar with the epidemic curve and understand concepts such as 'flatten the curve'," she said.
"The epidemic curve is very similar to the pest infestation curve, which we use to explain the status of various pests - from newly arrived to widespread - and which management actions should take place at various places along the curve.
"Although there are differences in terminology used in epidemiology, this new-found knowledge that New Zealanders have makes it easier for us to communicate that eradication is most suited for newly-arrived pests that aren't yet widespread, while for widespread species we should focus on protecting our assets, such as conservation areas.
"We'll need to build on this pandemic communication platform for biosecurity."
Kiwis report around 10,000 suspected pests and diseases to the Ministry for Primary Industries each year, of which 750 lead to formal investigations.
Pests are estimated to cost our primary sector around 1.15b each year, with a new plant establishing itself in the wild every 39 days on average.