(A) The insect faced decline, now is the focus => needs AND or some other conjunction
(B) The insect faced decline, has now become the focus => needs AND or some other conjunction
(C) The insect faced decline, and now is the focus => Seems correct as no error as such(D) The insect faced decline now, is the focus => needs AND or some other conjunction and also the placement of the word "now" is incorrect
(E) The insect faced decline; now is the focus=> No independent clause after the semicolon.