The source of the cattle disease Mycoplasma bovis will probably never be found, a Parliamentary Select Committee has been told.
Despite that, the Ministry for Primary Industries (MPI) said it was continuing to investigate and overall confidence was edging upwards.
This information came when staff from the ministry appeared before Parliament's Primary Production Select Committee yesterday.
They said they had done 250,000 tests, and had spent $110 million on fighting the disease and $33m on compensation for disease-hit farms.
But MPI director of M bovis response Geoff Gwyn was pessimistic about ever finding out how the disease came in to New Zealand.
"We still have investigations ... and none of those investigations to date have uncovered a smoking gun.
"My view is that we will never get that smoking gun. That said, we will continue to exhaust every avenue of inquiry to do that."
However, Mr Gwyn said he was quietly optimistic about his chances of success against the cattle disease because of what had been learned from milk testing.
"If this [disease] had been endemic in New Zealand or established in New Zealand, then bulk milk testing in New Zealand would have been on fire; we would have found hundreds of cases but we didn't."
MPI is hiring more eradication experts on long-term contracts.
Stink bug: 'They didn't fly out, they just crawled around'
MPI officials have also faced questioning on the brown marmorated stink bug, an insect native to China, Japan and Korea.
They told the committee 213 bugs had been found since September, of which 32 were alive.
Biosecurity officials said the bug was spreading fast across the world, but it was being blocked here.
MPI official Steve Gilbert cited the case of one alert by someone in Ōamaru who found 26 bugs in a box of running shoes bought from America via E-Bay.
"He just opened the box, they didn't fly out, they just crawled around, and he was a very good.
"He took them to his bathroom, locked the door, captured them, put them in an Agee jar, and put them out of their misery."