Insecticidal effect of metabolites identified in edible mushrooms against Rhyssomatus nigerrimus Fahraeus

Excessive use of insecticides has led to resistance of some pathogenic organisms (nematodes, bacteria and fungi), environmental contamination, and the presence of hazardous residues. Therefore, the aim of the present study was to evaluate synthetic metabolites derived from previous studies with edible mushrooms against the soybean weevil Rhyssomatus nigerrimus Fahraeus (Curculonidae) because of the relevance of pest control in an economically important crop. Furthermore, this is one of the first studies where edible fungal molecules are evaluated for the control of these insects. Initially, two in vitro tests (toxic effect and immersion) were evaluated against R. nigerrimus. In these tests, sensitivity and viability were determined in the 2% Tween control in water. For these two tests, the synthetic metabolites pentadecanoic acid (PNA), palmitic acid (PMA), stearic acid (STA), linoleic acid (LNA), β-sitosterol (βT) were evaluated individually as well as in combinations, "the fraction of standards (E1)". Based on the results obtained, the dip test was selected to evaluate the mixtures of two standards (1. PMA + βT, 2. PMA + PNA, 3. PMA + LNA, 4. PMA + STA, 5. STA + βT, 6. STA + PNA, 7. STA + LNA, 8. PNA + βT, 9. PNA + LNA, 10. LNA + βT), three (1. PNA + βT + LNA, 2. PNA + βT + STA, 3. STA + LNA + PNA and 4. STA + LNA + βT) and four (PNA, βT, LNA and STA). The results showed that the mixture of three standards caused a higher percentage of mortality relative to the control group: l. PNA + βT + LNA and 2. PNA + βT + STA with 54.44 and 48% mortality of R. nigerrimus insects exposed for 15 days. These results show the importance of evaluating mixtures of molecules against R. nigerrimus.