NASUULU CONSERVANCY, Kenya (AP) — As locusts by the billions — yes, billions — descend on parts of Kenya in the worst outbreak in 70 years, small planes are flying low over affected areas to spray pesticides in what experts call the only effective control.

It is challenging work, especially in remote areas where mobile phone signals are absent and ground crews cannot quickly communicate coordinates to flight teams.

The ground crews are in “the most woeful terrains,” Marcus Dunn, a pilot and the director at Farmland Aviation, said Saturday. “If there is no network, then the fellow on a boda boda (motorcycle), he has to rush off now and go and get a network.”

Just five planes are currently spraying as Kenyan and other authorities try to stop the locusts from spreading to neighboring Uganda and South Sudan. The United Nations has said $76 million is needed immediately to widen such efforts across East Africa.

A fast response is crucial. Experts warn that if left unchecked, the number of locusts could grow by 500 times by June, when drier weather will help bring the outbreak under control.

The finger-length locusts swept into Kenya from Somalia and Ethiopia after unusually heavy rains in recent months, decimating crops in some areas and threatening millions of vulnerable people with a hunger crisis.

Somalia’s agriculture ministry on Sunday called the outbreak a national emergency and major threat to the country’s fragile food security, saying the “uncommonly large” locust swarms are consuming huge amounts of crops.

In swarms the size of major cities, the locusts also have affected parts of Sudan, Djibouti and Eritrea, whose agriculture ministry says both the military and general public have been deployed to combat them.

Kenya’s agriculture minister has acknowledged that authorities weren’t prepared for the scope of the infestation this year. That’s not surprising, considering it’s been decades since the country’s last comparable outbreak, U.N. officials say.

The locusts also are heading toward the breadbasket of Ethiopia, Africa’s second-most populous country, in that nation’s worst outbreak in 25 years. On Thursday, startled residents of Ethiopia’s capital, Addis Ababa, started reported sightings of the insects.

“I was surprised to find the locusts inside my living room,” said one resident, Mathewos Girma, showing a photo on his mobile phone.