Apparently this practise has been going on for decades and most airlines have phased it out but it's still at the pilots discretion in some cases and some countries mandate that planes be sprayed. Most of the time it is done before the passengers board but not all the time.
Now for someone that never uses pesticides around the house, (i have a fly killer, will swat), this sort of thing is quite alarming. Sure i understand about the insect threat to national food security, especially in places like australia. But what about people with sensitivities to these chemicals or those that have prolonged exposure to them. Apparently flight attendants have started to bring cases against airlines for these practises. It's just funny that i never knew about this before. So unusual that i thought i'd bring it to everybody's attention.