The radial diffusion of an enzyme in agar gel containing substrates allows the determination of hydrolytic activity if the distinction between substrates and product is possible. In this way, a qualitative analysis of some digestive enzymes of the gut of Anticarsia gemmatalis was carried out.  The production of amylases, lipases and proteases by soy caterpillars in fifth instar created with soy leaves and artificial diet was tested.  The three guts were removed  and macerated in 1mL HCl 10^-3 M in order to obtain the homogenate. A volume of 25mL of media supplemented with substrates was autoclaved and placed in plates of Petri and some holes were made in order to place 100μL of extract.  The plates were incubated at 30°C for 120h and observed daily. The plate containing 0.1% of starch for detection of amylase was disclosed with iodine solution.  The iodine reacts with starch forming a blue complex.  Thus, the appearance of bright zones around the hole indicates the degradation of the starch chains through the action of amylase.  The medium containing 1% of olive oil (pH 9,0) for the detection of lipase was disclosed with solution of phenolphthalein.  When the lipids present in the media were degraded, there was a formation of fatty acids and the reduction of pH. In this way, the area where the extract spread out became bright.  As for the detection of proteases, it was directly observed in the medium containing sodium caseinate as substrate. The protease activity was negative when no clear area was present and positive when the zone of proteolysis was visible. Several methods, such as colorimetric analysis or use of zymographic techniques, are available for the analysis of enzyme activity. However, the incorporation of different substrates in plates with nutrient agar allowed the initial detection of extracellular hydrolases produced by Anticarsia gemmatalis. Although it cannot be used to quantify the substrate degradation, the simplicity of this method comprises its greatest advantage.