The country's border patrol teams have had their busiest summer on record, issuing almost 4000 infringement notices to people trying to bring in risky goods.
The most common interception - almost three quarters of the total - was undeclared food.
But, the brown marmorated stink bug was also a problem and got stopped 180 times at the border.
Ministry for Primary Industries border clearance director Steve Gilbert said in one instance that meant turning away four container ships carrying cars from Japan.
"We detected either live or recently dead [bugs] in such numbers that we felt we would not be able to treat the vehicles sufficiently well on discharge so to us, there was no other alternative but to ask them to leave New Zealand waters," he said.
Mr Gilbert said they expected the influx in seizures from visitors, but they did not expect so many interceptions through the mail centre.
"Increases in the mail pathway was somewhat of a surprise - internet shopping is certainly booming."
"The big challenge for us in the mail centre is seeds. The numbers of people that are purchasing seeds very very cheaply by internet and whether those seeds are what they say what's in the packet or whether they're something else that could be a threat to NZ."
Two million passengers arrived by plane between December and February.
Mr Gilbert said most people who had an undeclared item seized, were not aware they had done anything wrong.
"With the pressures of international travel they just clean forgot about it. People in the main do not endeavour to smuggle biosecurity-risk goods in, it's either a lack of awareness of they just simply forgot."
He said the strangest thing biosecurity staff had to wrangle was a cockatoo that decided to come across the Tasman on a cruise ship.
"Basically it decided to come to New Zealand and have a look around, we took some lengths to rehabilitate it with it's owner in Brisbane. That was probably the event of the summer."