Well it's hard to know what fitness terrain lay between the present phenotype and that one, so it's necessarily obvious bthat such an adaptation would occur. Nor is it obvious that stripe attraction is more adaptive. Could be hidden costs I'm not cognizant of. In any case, we were speaking of the zevras adaptation, not the mosquito's. If true that mosquitos are not attracted to striped things, it doesn't matter why zebras have stripes. What matters is the cost to mosquitoes presently incurred by missing out on all that zebra. Indeed, one wonders why mosquitos haven't adapted to the zebras stripes already...