Nowhere in Africa

In 1938, the Redlich family flees to Kenya from LeobschÃ¼tz in Silesia, Nazi Germany, to escape the increasing persecution of the Jews. Walter, a former lawyer, finds work as a farm manager and sends for his family. His wife Jettel has trouble adjusting to life in Africa, although their daughter Regina quickly adapts to her new environment, easily learning the language of the country and showing interest in local culture. Regina soon forms a close friendship with the farm's cook, Owuor, who helped save Walter's life when he had malaria. The only German contact that Jettel has is through a friend of Walter's named SÃ¼sskind, an ex-German who has lived in Africa for years. Jettel asks SÃ¼sskind why he was never married, and he states that he had a habit of falling in love with married women.
When war breaks out, the British round up all German citizens, and hold them, whether Jew or gentile, separating men from women. The Redlichs' marriage begins to deteriorate and Walter accuses Jettel not wanting to sleep with him since he is only a farmer. Jettel sleeps with a German-speaking British soldier to secure work and a home on a farm for the family, and Regina and Walter both find out.
Walter decides to join the British army and wants Jettel to go to Nairobi with him, but she refuses and stays to run the farm with Owuor. Regina is sent to an English boarding school, and is kept there for years, only being able to come back every so often during the harvest season. Jettel becomes fluent in Swahili and runs the farm competently, gaining an appreciation for African culture and hard work that she did not have before. During this time, Jettel and SÃ¼sskind develop a relationship (whether they slept together or not remains unclear).
Walter comes back from the war and an overjoyed Jettel sleeps with him. Later, he tells her that his father was beaten to death and his sister died in a concentration camp. He applies for a law position in Germany and receives word that he can immediately be placed as a judge. and states that the British army's policy is to send all soldiers and their families back home. Jettel refuses to go with him, saying the farm needs her and that she is tired of following him around.She also refuses to believe that a country that killed their relatives could ever really be considered home. An angry Walter replies that she hated Africa at first and couldn't wait to get back to Germany, and that she is being selfish. Walter asks Regina if she wants to go with him, but Regina does not want to leave Owuor.
As Walter is preparing to leave alone, swarm of locusts appears and threatens the harvest. Jettel sees Walter returning to fight off the locusts, and is touched at his dedication to the family. Eventually the locusts leave without serious damage the crops and the farmers celebrate. Jettel and Walter make love and reconcile, and she tells him that she is pregnant with his child. Owuor decides to go on a journey, realizing that the Redlichs' life is back in Germany, and he and Regina tearfully say good-bye. Jettel allows Walter to decide whether or not they should leave, and he acquires tickets back to Germany.
The final scene shows Walter, Regina, and Jettel traveling on an African train, as the train stops, and an African woman offers Jettel a banana, only to show her how much Africa meant to her. In a narration, Regina states that her brother was born healthy and was named Max, after Walter's deceased father.

Question: What threatened the harvest?
Answer: locusts