Five invasive alien plant powders, Norway spruce (Picea abies [L.] H. Karst.) wood ash and diatomaceous earth against Sitophilus oryzae (L.) adults: are they closer to guns or roses?

Abstract

We tested the insecticidal efficacy of different powders as surface treatment against the rice weevil (Sitophilus oryzae) adults. We have applied dusts from five invasive alien plant species (Solidago canadensis, Solidago gigantea, Amorpha fruticosa, Rhus typhina, Ailanthus altissima) and two inert dusts, i.e. wood ash from Norway Spruce (Picea abies) and commercial product SilicoSec® (as diatomaceous earth). Mortality was evaluated from 1st till 7th day after exposure, at 20 and 25 °C, two values of relative humidity and two doses (20 and 40 g/m2). After Day 7, alive beetles were placed into clean Petri dishes, and mortality counts were measured from 8th till 14th day. In general, we have detected poor efficacy of plant powders against S. oryzae. SilicoSec® at 20 g/m2 caused 100 % mortality at 25 °C and 55% RH, after seven days. Wood ash (13.46% SiO2) was less effective in comparison to SilicoSec® (79.48% SiO2), as approx. 60% mortality was recorded at the same conditions. We have detected that leaves of A. altissima and flowers od S. gigantea are rich with polyphenols (like catechin hydrate), on average almost 17 mg/g in S. gigantea flowers. Flowers and leaves of Solidago species are also rich with essential oil, like beta-copaene. The results of our research indicate that the powders of invasive plants are closer to fragrant roses in controlling S. oryzae adults, while the gun for this pest is only diatomaceous earth. To improve the effectiveness of invasive plant products, we suggest testing their independent effectiveness in liquid form as well as combinations of their essential oils with inert dusts.