Atividade larvicida de Piper alatipetiolatum e Piper purusanum contra Aedes albopictus Skuse, 1984 ( Diptera: culicidae)

Abstract

Aedes albopictus is the main vector of several arboviruses such as Dengue, Zika and Chikungunya, in some countries where the thermal barrier is a limiting factor for Aedes aegypti. The use of plant products such as extracts and essential oils to control these mosquitoes has increased in the last decades, due to the need to discover new compounds with insecticidal activity, since populations of these vectors have shown resistance to the synthetic insecticides used. In this way, the objective of this study was to evaluate the larvicidal potential of methanolic extracts and essential oils obtained from leaves of P. alatipetiolatum and P. purusanum against immatures of A. albopictus under laboratory conditions. The selective bioassays were performed in triplicate with two replicates, consisting of a control group (Cont-1 and Cont-2) and three concentrations of the extract or essential oil of botanical species (125, 250 e 500 ppm); the doses were done in quintupleta with five replicates and seven concentrations of the essential oils, which were from 25 to 175 ppm for P. alatipetiolatum and 50 to 200 ppm for P. purusanum. Mortality was verified at the intervals of 24, 48 and 72 h. The data were submitted to Analysis of Variance (ANOVA), followed by the Tukey Test (α = 0.05) by the program Bioestat 5.3 and the efficiency of the essential oils was compared by the values of the lethal concentrations (LC50 and CL90), by the Probit model. The results showed that the extract and the essential oil of both species have larvicidal activity on A. albopictus already in the first 24 h, however, the percentages of mortality caused by the extracts were low (maximum of 78.3 % for P. alatipetiolatum and maximum of 8.3 % for P. purusanum only at 500 ppm and after 72 h). The essential oil of both plant species presented activity from the lowest concentrations (25 and 50 ppm in P. alatipetiolatum, and 50 and 75 ppm in P. purusanum), however, it was verified that the mortalities in these concentrations did not differ significantly from the controls (p > 0.05). The results also showed that concentrations of 75 and 100 ppm of P. alatipetiolatum caused significantly different percentages of mortality between the control group and between the highest concentrations (125 to 175 ppm) at all observation intervals. However, concentrations of 125 to 175 ppm did not differ significantly from each other, and in the last observation interval (72 h) mortality at 100 ppm was equal to 125 and 150 ppm. For P. purusanum the concentrations of 100 to 200 ppm caused significantly different mortalities in the 24 h interval, but from 48 h it was observed that 125 and 150 ppm and 175 and 200 ppm showed no statistically significant difference. Therefore, from 48 h, for both species of piperaceae, the increase in exposure time was not directly proportional to the percentage of mortality, regardless of the concentration used. The lowest values of LC50 and CL90 obtained for P. alatipetiolatum confirm the best activity of this species on the vector mosquito, with potential to be used in future strategies of A. albopictus control, especially if studies are carried out to know the compounds that confer this larvicidal activity.