In Vitro Nematocidal Properties from Two Extracts: Lippia graveolens Leaves and Delonix regia Flowers Against Eggs and Infective Larvae of Haemonchus contortus

The objective of this study was to assay the ovicidal and larvicidal effects of two hydroalcoholic extracts (HA-E) and their aqueous fractions (Aq-F) and organic fractions (EtOAc-F) from Lippia graveolens (leaves) and Delonix regia (flowers) against the parasitic nematode Haemonchus contortus. The egg hatching inhibition test (% EHI) and mortality of infective larvae (% mortality) were used as biological models. The treatments of each plant (mg/mL, % EHI, and % mortality) were assigned as follows: HA-E (12.5-50, EHI; 25-200, mortality), Aq-F (6.25-25.00, EHI; 12.5-50, mortality), EtOAc-F (0.37-25, EHI; 3.12-50, mortality), negative controls (distilled water and methanol at 2% and 4%), and positive control (ivermectin at 5 mg/mL). Data were analyzed using a completely randomized design through an analysis of variance, considering the EHI and mortality percentages as the response variables. To identify the secondary metabolites, both plants were subjected to qualitative chemical analysis and HPLC. The results showed that both plants exhibited highly ovicidal and larvicidal effects. The bipartition in each HA extract allowed the increase of the anthelmintic effect in EtOAc-F, achieving a total ovicidal activity at 1.56 mg/mL and a larvicidal effect higher than 90% at 25 mg/mL. The qualitative chemical profile of both vegetal species identified alkaloids, flavonoids, condensed tannins, terpenes, and saponins. These results suggest that either L. graveolens leaves or D. regia flowers could be potential candidates for the control of parasitic gastrointestinal nematodes in small ruminants. However, in vivo studies with experimental animals to evaluate their possible toxicity and anthelmintic effect are necessary.