Medieval sources (Nachmanides Exodus 10:14) write that locust plagues
have not affected Egypt with significant crop loss since the Biblical
plague of locust. Can this be verified? Is there a scientific
explanation?(The Egypt referred to is
Biblical Egypt which is centered near the North Nile area.)

(I am aware that locusts were recently in Cairo but most died as they
landed and there was no reported crop loss. Also, western and
Southeastern Egypt have been affected by locusts in the past but that
is not Biblical Egypt. In 1956, I believe, National Geographic had a
cover story on this or a similar phenomenon)

I hope that these quotes might be of some help.

http://en.wikipedia.org/wiki/Desert_locust
" When exposed to the adult pheromone, hoppers become confused and
disoriented, because they can apparently no longer "smell" each other,
though the visual and tactile stimuli remain. After a few days, the
hopper bands disintegrate and those that escape predation become
solitary again. Maybe this effect could aid locust control in future."

http://www.pittsburghlive.com/x/tribune-review/middleeastreports/hiel/s_274342.html
{
"They are driven by strong winds. ... Under current climatic
conditions, they will not likely cause damage," Christian Pantenius, a
locust expert with the United Nations Food and Agriculture
Organization (FAO), told Reuters.

He said locusts do not feed when temperatures drop below 30 degrees
Celsius (86 degrees Fahrenheit). Weather forecasters predict
temperatures here will remain about 77 degrees in coming days, and
Pantenius predicted the locusts will die or migrate south.
}