Background:The whitefly (Bemisia tabaci Genn.) is a widely distributed and highly harmful plant pest species. The management of B. tabaci has been typically carried out by chemical pesticides. In the last decade however, there has been an increasing interest in natural products, particularly those of plant origin, to control this pest species. In the present work, aqueous and ethanolic extracts of native plants from the flora of the Yucatán peninsula (Acalypha gaumeri, Annona squamosa, Carlowrightia myriantha, Petiveria alliaceae and Trichilia arborea) and the introduced plant Azadirachta indica were collected and evaluated for insecticidal activity against eggs and nymphs Bemisia tabaci. Results: Most of the aqueous and ethanolic extracts showed high insecticidal effects on B. tabaci eggs. The lowest LC 50 values were recorded in the aqueous extracts of A. gaumeri (0.39% w/v), A. squamosa (0.36% w/v), P. alliaceae (0.42% w/v) and A. indica (0.30% /v), as well as in the ethanolic extracts of P. alliaceae (2.09 mg mL -1 ) and T. arborea (2.14 mg mL -1 ). On the other hand, B. tabaci nymphs were not affected by the aqueous extracts, but were highly sensitive to the ethanolic extracts of the tested plants. The lowest LC 50 values were recorded in the ethanolic extracts of P. alliaceae (1.27 mg ml -1 ) and T. arborea (1.61 mg mL -1 ). The GC-MS analysis showed that phytol was the major component of the ethanolic extract of P. alliaceae and fatty acids were the major components of ethanolic extract of T. arborea. Conclusions: Overall, results suggest that ethanolic extracts of P. alliaceae and T. arborea leaves showed the highest insecticidal effects on eggs and nymphs B. tabaci. The extracts from P. alliaceae and T. arborea are good candidates to be developed as sources of natural insecticides for the management of immature B. tabaci since their effects were comparable with that showed by the extracts of A. indica, a well-known plant species for its insecticidal activity.

Eugenia winzerlingii (Myrtaceae) is an endemic plant from the Yucatan peninsula. Its organic extracts and fractions from leaves have been tested on two phloem-feeding insects, Bemisia tabaci and Myzus persicae, on two plant parasitic nematodes, Meloidogyne incognita and Meloidogyne javanica, and phytotoxicity on Lolium perenne and Solanum lycopersicum. Results showed that both the hexane extract and the ethyl acetate extract, as well as the fractions, have strong antifeedant and nematicidal effects. Gas chromatography-mass spectrometry analyses of methylated active fractions revealed the presence of a mixture of fatty acids. Authentic standards of detected fatty acids and methyl and ethyl derivatives were tested on target organisms. The most active compounds were decanoic, undecanoic, and dodecanoic acids. Methyl and ethyl ester derivatives had lower effects in comparison with free fatty acids. Dose-response experiments showed that undecanoic acid was the most potent compound with EC50 values of 21 and 6 nmol/cm2 for M. persicae and B. tabaci, respectively, and 192 and 64 nmol for M. incognita and M. javanica, respectively. In a phytotoxicity assay, medium-chain fatty acids caused a decrease of 38–52% in root length and 50–60% in leaf length of L. perenne, but no effects were observed on S. lycopersicum. This study highlights the importance of the genus Eugenia as a source of bioactive metabolites for plant pest management.

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