Extract from the roots of Saponaria officinalis as a potential acaricide against Tetranychus urticae

Abstract

The two-spotted spider mite (Tetranychus urticae Koch.) is one of the most harmful phytophagous pests, dangerous not only due to its fast development cycle and high fertility, but also due to its ability to rapidly develop resistance to active substances of acaricides. It is therefore important to seek new alternative products characterized by a novel mechanism of action while being safe to health at the same time. For this reason, we tested the efficacy of extracts obtained by extraction of the roots of Saponaria officinalis in water against all developmental stages of T. urticae. The highest sensitivity was found for eggs (LC50 = 0.31% w/v), while adults showed the least significant sensitivity (LC50 = 1.18% w/v). Application of the extract also resulted in an inhibition of oviposition by females (LC50 = 0.91% w/v). The efficacy of extract prepared by maceration of 15 and 30 g of S. officinalis roots in one litre of water was verified in one-year greenhouse tests in cucumbers and tomatoes infested by T. urticae. Repeated applications of the extract were found to significantly reduce the numbers of two-spotted spider mite individuals on tomato and cucumber leaves, and their counts remained significantly lower compared to untreated plants throughout the observation period (140 days). The extract, prepared from 30 g of the roots in one litre of water, maintained spider mite counts at approximately the same levels as an applied commercial acaricide based on a.i. abamectin. At the same time, it was observed that the extract had a positive effect with respect to the mean weight of the fruits and to the overall yield of tomato and cucumber fruits, compared to untreated plants. In addition, the amounts of substances extracted from the roots of S. officinalis using water, as well as the extraction velocity of water-soluble substances, were studied. The amounts of water-extractable substances were found to be directly dependent on the weights of the extracted roots, where the extraction of 15, 30, 60, 80 and 100 g of roots in one litre of water resulted in 7.4, 15.9, 30.6, 38.9 and 49.4 g of dry mass of the substances, respectively, dissolved in one litre of the extract after 24 h. Also, the extraction velocity at ambient temperature was very high. When 30 g of roots was extracted in one litre of water, most of the substances were dissolved during the first 10 min (12.9 g L−1); subsequently, the amounts of dissolved substances kept rising only slightly and stabilized after about 25 min from the beginning of extraction (15.5 g L−1). Given that the root extract is primarily used in the food industry, in traditional medicine and in the cosmetics industry, we can presume that the use of the extract for the protection of vegetables against T. urticae is of no concern. Based on our tests, we can propose this extract as a candidate basic substance that may be beneficial for reducing the counts of harmful developmental stages of T. urticae.