Field trials in Greece showed that beneficial fungi—Beauveria bassiana and Cordyceps fumosorosea—successfully reduced infestations of the invasive citrus spiny whitefly (Aleurocanthus spiniferus) on orange trees. The biological treatment cut pest populations and leaf damage nearly as effectively as chemical pesticides, with the strongest results at the egg and early nymph stages. The fungi worked by infecting pests directly while leaving beneficial insects unharmed, offering a sustainable, pesticide-free strategy for integrated pest management in citrus orchards.