We tested the bioactivity of aqueous extracts of Ludwigia spp. (Myrtales: Onagraceae) on the biological cycle of Plutella xylostella. We assessed the duration of and viability during the larval, pupal and adult phases, as well as the influence of the extracts on the fecundity and hatching of P. xylostella eggs. Subsequently, we phytochemically screened the extracts. The extracts of L. tomentosa and L. longifolia reduced the pupal weight instead of prolonging the larval stage of P. xylostella. The L. tomentosa effect caused higher larval mortality and reduced the fecundity and hatching of P. xylostella eggs, and L. sericea reduced the egg survival. The phenolic compounds—flavonoids, condensed tannins and alkaloids—were more abundant in L. nervosa, L. tomentosa, L. sericea and L. longifolia. The L. tomentosa, L. longifolia and L. sericea extracts were bioactive, and these species showed the best results regarding their ability to control P. xylostella populations, because these plants produce substances able to inhibit food consumption and interfere with the morphological and physiological transformations of the offspring and the oviposition of adults.

The indiscriminate use of synthetic insecticides caused an increase in the resistance of Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) to almost all classes of insecticides, as well as affected the environment and non-target organisms. Thus, the search for less harmful alternatives with the purpose of reducing the application of these insecticides has become a priority. A possible alternative to reduce the use of synthetic insecticides is by using botanical insecticides, given the thousands of existing compounds derived from secondary metabolism in plants. In this study, we tested the following hypotheses: (i) the aqueous and ethanolic extracts of native plants reduce the food consumption of larvae and oviposition of adults of P. xylostella; (ii) these botanical species can act as potential plant insecticides. The objective of this work was to evaluate the effect of plant extracts on the feeding preference of larvae and oviposition of adults of P. xylostella. For this, cabbage discs treated with aqueous and ethanolic extracts of Schinus terebinthifolius, Annona coriacea, Annona crassiflora and Serjania marginata were given to larvae. The concentrations used for the aqueous extracts were of 5 and 10 mg mL-1, and for the ethanolic extracts were of 1 and 5 mg mL-1. Both extracts of the four tested plant species showed oviposition suppressed. The extract of S. marginata showed the lowest rates of suppression. All treatments with ethanolic extracts showed a phagodeterrant effect being that the aqueous and ethanolic extracts of A. crassiflora and S. terebinthifolius were the most effective as antifeedants on third instar larvae by P. xylostella.

Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) is an insect pest that causes great damage to Brassica cultures. It is necessary to develop alternative control methods, because this pest is resistant to many synthetic insecticides that are harmful to the environment. The objective of this study was to evaluate the effects of aqueous extracts of Campomanesia adamantium, C. guazumifolia, and C. xanthocarpa on the life cycle of P. xylostella. These aqueous extracts were prepared in a concentration of 10 g/mL and then applied on cabbage disks of 4 cm2 to feed the larvae until they reached pupal stage. The disks were evaluated daily during the larval stage and replaced every 24 hours. The experiment consisted of ten replicates, each replicate containing five subsamples. The parameters evaluated were larval and pupal survival, pupal biomass, gender ratio, male and female longevity, number of eggs, fecundity, oviposition period and egg survival. The C. xanthocarpa extract increased larval stage and decreased pupal biomass and oviposition period. The C. adamantium extract decreased larval duration, pupal biomass, male longevity, and oviposition period. The C. guazumifolia extract decreased larval stage, male longevity, and oviposition period. The chemical composition of the extracts of Campomanesia species presented flavonoids such as quercetin, phenolic compounds, and tannins, and the highest retention time occurred in C. adamantium. Thus, the extracts of Campomanesia species were effective in decreasing and controlling the oviposition period of P. xylostella, probably because of the presence of flavonoids, which indicates a possible antioxidant potential and, therefore, the observed antibiosis.

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