Beauveria bassiana interacts with gut and hemocytes to manipulate Aedes aegypti immunity

Abstract

Background Mosquito-borne diseases affect millions of people. Chemical insecticides are currently employed against mosquitoes. However, many cases of insecticide resistance have been reported. Entomopathogenic fungi (EPF) have demonstrated potential as a bioinsecticide. Here, we assessed the invasion of the EPF Beauveria bassiana into Aedes aegypti larvae and changes in the activity of phenoloxidase (PO) as a proxy for the general activation of the insect innate immune system. In addition, other cellular and humoral responses were evaluated. Methods Larvae were exposed to blastospores or conidia of B. bassiana CG 206. After 24 and 48 h, scanning electron microscopy (SEM) was conducted on the larvae. The hemolymph was collected to determine changes in total hemocyte concentration (THC), the dynamics of hemocytes, and to observe hemocyte-fungus interactions. In addition, the larvae were macerated to assess the activity of PO using L-DOPA conversion, and the expression of antimicrobial peptides (AMPs) was measured using quantitative Real-Time PCR. Results Propagules invaded mosquitoes through the midgut, and blastopores were detected inside the hemocoel. Both propagules decreased the THC regardless of the time. By 24 h after exposure to conidia the percentage of granulocytes and oenocytoids increased while the prohemocytes decreased. By 48 h, the oenocytoid percentage increased significantly (P < 0.05) in larvae exposed to blastospores; however, the other hemocyte types did not change significantly. Regardless of the time, SEM revealed hemocytes adhering to, and nodulating, blastospores. For the larvae exposed to conidia, these interactions were observed only at 48 h. Irrespective of the propagule, the PO activity increased only at 48 h. At 24 h, cathepsin B was upregulated by infection with conidia, whereas both propagules resulted in a downregulation of cecropin and defensin A. At 48 h, blastospores and conidia increased the expression of defensin A suggesting this may be an essential AMP against EPF. Conclusion By 24 h, B. bassiana CG 206 occluded the midgut, reduced THC, did not stimulate PO activity, and downregulated AMP expression in larvae, all of which allowed the fungus to impair the larvae to facilitate infection. Our data reports a complex interplay between Ae. aegypti larvae and B. bassiana CG 206 demonstrating how this fungus can infect, affect, and kill Ae. aegypti larvae. Graphical Abstract

Effect of endophytic entomopathogenic fungal conidia and blastospores induced in maize plants by seed inoculation on Spodoptera frugiperda immune response and mortality

“…Plasmatocytes and granulocytes are mainly involved in encapsulation and phagocytosis. At the same time, oenocytes are related to nodulation and melanization, and granulocytes and oenocytoids adhere to the fungus, demonstrating both hemocytes' involvement in stopping the fungal infection (Bitencourt et al 2023).…”

“…The endophytic EPF with 1 x 1010 conidia mL-1 propagules did not cause an immune response in S. frugiperda larvae. The immune response in insects is indicated by increasing the hemocyte concentration in the larvae hemolymph of insect hosts (Bitencourt et al 2023). This study could not detect propagules of the endophytic EPF invading the hemocoel or penetrating the integument of the S. frugiperda larvae.…”

“…There is no information about the response of S. frugiperda larvae that consume leaves inoculated with the endophytic EPF from South Sumatra. Nevertheless, much information shows insect immune responses to EPF that are applied topically (Enríquez-Vara et al 2012;Bitencourt et al 2023). This research's novelty was to detect the effect of the endophytic entomopathogenic fungal conidia and blastospores induced in maize plants by seed inoculation on S. frugiperda's immune response and mortality.…”

Recent Advancements in Pathogenic Mechanisms, Applications and Strategies for Entomopathogenic Fungi in Mosquito Biocontrol

“…aegypti larvae, leading to a decrease in the total hemocyte concentration and the inability to stimulate the phenoloxidase activity, which is a proxy for the general activation of the innate immune system of the insects. This downregulation of the immune response also downregulates the expression of antimicrobial peptides, enabling the fungus to impair the larvae and facilitate infection [44]. Furthermore, both B. bassiana and M. anisopliae can invade the hemocoel from the midgut of Ae.…”

“…Furthermore, both B. bassiana and M. anisopliae can invade the hemocoel from the midgut of Ae. aegypti larvae [44,45].…”