In Vitro Insecticidal Activity of Silica Nanoparticles and Simarouba Amara Against Arabica Coffee White Stem Borer, Xylotrechus Quadripes

Abstract

Xylotrechus quadripes, Chevrolet (Coleoptera: Cerambycidae) is one of the most lethal pests infesting Arabica coffee plants. The complex feeding habits and masked behavior of coffee white stem borer (CWSB) make pest management difficult despite the application of insecticides.  In addition, the pesticides are inaccessible to larvae because soon after hatching larvae burrow into the stem and feed inside until they emerge as adults. In this regard, we developed a novel environment friendly biopesticide to combat CWSB. The activities of Nanosilica (NSi) and Simarouba amara bark extract (SABE) were evaluated by incorporating these in the artificial diet, mimicking the host plant environment. We also studied the impact of biopesticides on fecundity, fertility, larval penetration in cut stems, toxicity and olfactory responses of Xylotrechus quadripes.  Both NSi and SABE exhibited dose-dependent mortality rates, demonstrating their effectiveness as biopesticides.  On an average, the number of eggs laid on treated and untreated (control) cellulose sheets was found to be 3-4 and 18 in the NSi- and SABE-treated groups, respectively, compared to the control (25-35 eggs).  The eggs in fertility study revealed a significant hatching difference between the NSi and SABE-treated groups. NSi strongly inhibited the penetration, whereas SABE-treated stems allowed 2-3 penetrations of larvae, suggesting the operation of different larvae penetration mechanisms.  The toxicity study of NSi and SABE showed LC50 values of 257.63 and 575.43 mg/L respectively. The highest Olfactory avoidance response was observed in the NSi powder form (83.34%), followed by NSi-coated cut stems (76.67%) and SABE in solution form (73.34%). Thus, both NSi and SABE provide an effective alternative for integrated pest management in coffee arabica.