Very interesting, but I am going to totally disagree with the lecturer
Insects hatch in the evening as they have a far greater chance of survival from predators (plus they have spent the day warming up). It is not just insects, just look around you in the evening...the rabbits are out, the foxes are out, the deer are out, etc etc. The low light levels allow for a greater chance of remaining undetected.
The reason why there is a bigger rise in the evening is simply because there is a bigger hatch of insects! Exactly the same as saying how come you see more people in Tesco than you do in the corner shop..there are more things to chose from so you will see more people competing for more items...hence the evening rise
The Brown trout especially is adapted for surface feeding, that is why its eyes are more ontop of its head than say a rainbow. It has also adapted to being able to see shilouettes on the surface in low light because thats when there are more insects in the surface film.
I do not for one instance believe a hatching insect would ever have the ability to see a trout approaching from below, even if it had human sight...coz its eyes are not set in its head so as to be able to see under the water.
Just my opinion though...