Hi Carlos, if you want to check whether the spots are fungi or not then you can try to culture it on Sabouraud's broth or agar. 

Hi Carlos

I recomended you, use special staining for fungi like Blue metylen, Safranina for observe it in Microscope, and them try to culture a piece of sample in Sabouraud dextrosa and PDA Agar plus antibiotics.  Good luck

Hi Carlos

I agree other recommendations and you can culture a sample of those block spotson PDA or after surface sterilization directly culture a little  piece of spots on PDA or SDA (Sabaraud-Dextrose Agar). Good luck

Dear Carlos,

these spots really looks like inoculation by fungi. To chek it, you can place ded larva in Petri dish with wetted  filter paper or with solid agar surface. In a few days you will see if  the mycelium appear on larva or bacterial spot appear on  surface of agar .