Every plane is. https://www.agriculture.gov.au/biosecurity-trade/aircraft-ve...

Probably depends on where the plane is coming from. Source: me who just returned from Europe last week, no spraying. And have traveled internationally several times in the last few years and also no spraying.

From the link:

"Benefits of entering a voluntary formal arrangement include:

* disinsection methods are undertaken while passengers are not on the aircraft."

Used to see someone wandering down the aisles with spray cans on arrival - but not on the last several trips to Oz.

I was interested in this because it happened the last time I returned to NZ, but I hadn't seen it before. There are several approved methods and it depends on the airline. The method that doesn't involve spraying with you onboard is more expensive so tends to be used by budget airlines, and also airlines who might rotate their planes and crew around routes more often because it is a treatment that lasts for weeks.