Extratos vegetais ricos em proteases no controle in vitro de Pa-nagrellus sp. e Tenebrio molitor

Abstract

The objective of this study was to evaluate the activity of plant proteases on agricultural pests. As sources of proteases, latex from green papaya fruits (Carica papaya) and extracts from the peel and crown of pineapple fruits (Ananas comosus) were used. A standard tyrosine curve was used to measure enzyme activity and the Bradford method to measure protein content. Commercial papain and extracts boiled for 2 hours were used as a source of denatured proteases to compare the effect with the active extracts. To evaluate the proteolytic activity on nematodes, 20 μL of each extract diluted in distilled water at 5 mg/mL and 15 mg/mL, plus 10 μL containing approximately 50 Panagrellus sp., with 6 replicates, were placed in microtubes. The percentage of reduction was calculated after 24 and 48 hours of incubation at 28°C. To evaluate the toxicity of proteases in insects, larvae and pupae of Tenebrio molitor L. were immersed for 5 seconds in active and denatured extracts diluted to 15% (w/v) in distilled water. The number of dead larvae was recorded every 24 hours for 10 days. In addition to mortality, a change in the metamorphosis of surviving pupae was recorded. An artificial diet with wheat flour was prepared containing extracts at doses of 0, 100, 250 and 500 mg/g of flour. For each extract, 15 larvae were placed in a Petri dish containing 2.5 mL of diet and subsequently dried at room temperature (18 ºC ± 2 ºC) overnight. The weight and number of dead larvae were recorded every 24 hours and feeding behavior was evaluated seven days after treatment. The results indicate that the evaluated extracts caused a reduction in the number of Panagrellus sp. The papaya latex and papain proteases caused a reduction (p<0.05) in the number of Panagrellus sp. with values of 62.41% and 92.67%, and 52.33% and 89.71% for denatured and active extracts, respectively. The extracts evaluated in insects showed a toxic effect (p<0.05) on the larvae of T. molitor, mainly the proteases present in the pineapple peel and crown, since no mortality was observed for the active extracts, while the active latex and denatured caused, respectively, mortality of 98.89% and 43.33%. An effect (p<0.05) caused by the extracts on the mortality of T. molitor pupae was observed, but it was not sufficient to differentiate the extracts evaluated. The effect (p<0.05) on T. molitor pupae metamorphosis caused only by papain is attributed to proteases, since active papain resulted in the absence of wings in 53.3% of adults from pupae, not being malformation caused by denatured papain was observed. There was a strong feed reduction of 77.66%, a reduction in the relative rate of consumption of 0.08 mg/mg/day, a reduction in growth of -0.05 mg/mg/day and a reduction in the feed conversion efficiency of - 61.78% caused by papaya latex, with 500 mg/g of wheat flour. The results of this study demonstrate that plant proteases have potential for controlling agricultural pests.