Let me repeat that:
Evolutionary biologists claim, that after insect-species evolved the key evolutionary innovation – the ability of flight – then the ability got lost, and this happened independently, more than 1000 times in vast majority of insect orders …
Here is an older article from 1996:
WHY WOULD FLIGHTLESSNESS EVOLVE?
Why would natural selection repeatedly favor the loss of a structure which is generally attributed with being the key evolutionary innovation leading to the success of the group (see Daly, et al. quote above)? This question has intrigued insect systematists ever since Darwin.
and here is a more recent one from 2013:
Despite the advantages associated with flight, such as the ability to disperse widely and forage, flight has been independently lost within nearly every pterygote order and an estimated thousands of times overall
Have wings come, gone and come again?
Can complex traits be re-evolved by lineages that have lost them? Phylogenetic study now suggests that wings may indeed have reappeared several times within the ancestrally wingless stick insects.
stuff happens …