Mortality and Histopathology of the Digestive Tract of Schistocerca gregaria (Orthoptera: Acrididae) after Ingestion of Metarhizium acridum Spores

In this study, cross sections were made to observe the effect of Metarhizium acridum ( M. acridum ) on the mortality and the digestive tract histopathology of the desert locust Schistocerca gregaria (Orthoptera: Acrididae) after ingestion treatment. Teneral adult desert locusts were inoculated by gavage using a Hamilton syringe (taking care not to infect the mouthparts with spores) with 1 µL of three different concentrations (2.6 × 10 4 , 2.6 × 10 5 , and 2.6 × 10 6 spores/µL). Locusts demonstrated limited tolerance to the fungus, although the toxicity was significant for all three concentrations. High mortality was observed after the sixth day, with rates varying according to the number of spores inoculated. Upon the death of the insects from medium concentration, they were promptly dissected, and the digestive tract was immersed in the fixative. We prepared cross sections at different parts of the digestive tract of the locusts subjected to the intermediate concentration treatment and the control sample. The cross sections made indicate that the control intestine comprises healthy tissues; however, the infected gut exhibits alterations at all levels. M. acridum severely damages the tissues of the desert locust's digestive system. Our findings suggest that M. acridum can tolerate the intestinal conditions and damage the inner tissues of the desert locust gut.