。
Don't give in to temptation.
Literal
Temptation [to-に] lose-[gerund-て]-is-not-allowed.
誘惑 ('temptation, seduction') is formal vocabulary, Sino-Japanese compound from 誘 (invite) + 惑 (confuse, bewilder). 負ける ('to lose, be defeated') takes an に-marked thing being lost to. The whole construction 誘惑に負ける ('give in to temptation') is a useful idiomatic collocation. The ~てはいけない prohibition keeps it firm.