Incidence of microbial infections revealed by assessing nodulation in field-collected insects from Adana Province

Results of a field study designed to assess the extent of natural microbial infections in insects collected from agrarian fields surrounding Adana, Turkey, are reported. We identified and dissected specimens to assess the numbers of nodules. Formation of darkened melanotic nodules is the predominant cellular immune reaction to microbial and parasitic infection, and once formed, the nodules are permanently attached to internal surfaces. At least some nodules were found in 99% of 1200 examined specimens that were healthy in appearance. The number of nodules ranged approximately from 1 nodule/individual to >120 nodules/individual. We inferred that insects are regularly challenged by microbial and parasitic infections. The key implication of these data is that insect immune systems can limit the host range and effectiveness of microbial agents deployed in biological control programs. Future advances in the efficacy and use of biopesticides will depend on understanding and attenuating insect innate immune effector systems. Some insect pathogens have already evolved effective mechanisms to achieve this advance.