Are plant extracts safe for honey bees (Apis mellifera)?

Abstract

This work attempted to determine the effects of the aqueous extracts of Echinodorus grandiflorus, Origanum majorana, Punica granatum and Matricaria chamomilla on Africanized Apis mellifera workers, as well as their effects on the digestive tracts of these insects and chromatographic analysis of its compounds. For this, the methods of direct spraying, contaminating diets and treatment of contact surfaces (soybean leaves) were used. Five treatments were established: sterilized distilled water (control), aqueous extract of “leather hat” (E. grandiflorus), marjoram (O. majorana), pomegranate (P. granatum) and chamomile (M. chamomilla) at concentrations of 5%. Each treatment consisted of five replicates with 20 bees per replicate; each bee was an experimental unit. The workers of A. mellifera submitted to the treatments were conditioned in gearbox boxes, and these were kept in a climatic chamber (27 ± 2 °C, 60 ± 10% U.R.). The mortality of the workers was evaluated at different hours. The workers killed by the ingestion of contaminated paste were separated for midgut histological analysis. Plant extracts were submitted to chromatography. It was verified that all vegetal extracts reduced the survival of the workers of A. mellifera in all the bioassays. Plant extracts O. majorana and P. granatum caused morphometric changes, reducing the length of A. mellifera mesenteric cells. The extract of O. majorana showed a negative effect on A. mellifera; it reduced the survival of the workers in all the bioassays in which it was evaluated. It also caused morphometric alterations in the cells of the midgut.