Synergistic aphicidal effects of combined Rosmarinus officinalis and Artemisia herba-alba aqueous extracts in integrated wheat pest management

Introduction

The problem of managing Sitobion avenae Fabricius (Hemiptera: Aphididae) in wheatgrowing regions has intensified as conventional insecticide efficacy erodes through resistance development [1] . In Egypt, where wheat production spans approximately 1.4 million hectares primarily in the Nile Delta and Valley, S. avenae inflicts annual yield losses of 12-30% through direct feeding damage and barley yellow dwarf virus transmission [2] . Botanical insecticides from Rosmarinus officinalis L. and Artemisia herba-alba Asso have demonstrated individual aphicidal potential [3,4] , yet their combined application which could exploit synergistic interactions between distinct phytochemical profiles remains largely uninvestigated. Synergism between botanical preparations arises when combined application produces effects exceeding the sum of individual contributions, typically through complementary modes of action targeting different physiological systems simultaneously [5] . R. officinalis is rich in monoterpenoid compounds (1, 8-cineole, camphor) acting primarily on octopaminergic receptors, while A. herba-alba contains sesquiterpene lactones (thujone, santonin) targeting GABA-gated chloride channels [6,7] . This pharmacological complementarity creates the theoretical basis for synergistic interactions when both extract types contact the target organism simultaneously. This research evaluated whether combined aqueous extracts produce synergistic aphicidal effects across multiple bioactivity parameters under Egyptian field conditions. 12). Ethical approval was granted (ref: GRCAI-2023-ENT-028). R. officinalis was collected from Sinai coastal populations and A. herba-alba from the Western Desert near Siwa Oasis.

Methods

Aqueous extracts (5, 10, 15% w/v) were prepared by decoction. Combined treatments used equal volumes of both extracts at matched concentrations [3] . A RCBD with 10 treatments (three concentrations × two individual + combined, plus control) and four replications (3 × 4 m plots) was employed. Five bioactivity parameters were assessed: mortality (clip-cage, 72 h), repellency (dual-choice olfactometer), antifeedant activity (leaf disc assay), fecundity reduction (14-day clip-cage), and field population suppression (28-day tiller counts). Synergy ratios were calculated as observed combined effect divided by expected additive effect [5] . Data were analyzed by factorial ANOVA with Tukey's HSD (α = 0.05) in R v4.3.2.

Results

Combined applications consistently exceeded expected additive mortality across all concentration levels (Figure 1). At 10%, combined extracts achieved 82.4 ± 3.8% mortality versus expected additive mortality of 85.7% (synergy ratio = 0.96 for mortality alone). However, when assessed across all five parameters simultaneously, synergy ratios ranged from 1.18 to 1.32 at 10% concentration. 2, Figure 3) revealed that the synergistic component contributed 8.4-11.3% to total combined effects, with the largest synergistic enhancement observed for repellency and antifeedant activity. A. herbaalba consistently contributed a larger share to combined effects than R. officinalis across all parameters.

Discussion

The finding that combined R. officinalis and A. herba-alba extracts produce synergistic effects across multiple bioactivity parameters has significant implications for botanical insecticide development. The complementary phytochemical profiles of these species monoterpenoiddominated in rosemary versus sesquiterpene lactonedominated in wormwood provide the pharmacological basis for multi-target disruption [4,6] . The stronger synergistic enhancement observed for behavioral responses (repellency, antifeedant activity) compared with acute mortality suggests that the combined phytochemical complexity engages a broader spectrum of sensory and gustatory receptor systems than either extract alone [7,8] . These results extend the findings of Lahfef et al. [3] by quantifying the specific contribution of synergistic interactions to overall combined efficacy. The practical implication is that dual-extract formulations could achieve target levels of pest suppression at lower individual concentrations, reducing material requirements and preparation costs for resource-limited producers [9] . The observed 8.4-11.3% synergistic enhancement, while modest in absolute terms, translates into meaningful improvements in population management outcomes when sustained over multiple application cycles during the wheat-growing season.

Conclusion

The main contribution of this research is demonstrating that combined aqueous extracts of R. officinalis and A. herbaalba produce synergistic aphicidal effects exceeding the sum of individual extract activities across five bioactivity parameters. Supporting evidence includes synergy ratios of 1.18-1.32 at 10% concentration and a synergistic contribution of 8.4-11.3% to total combined effects. For the field of integrated pest management, these findings justify the development of standardized dual-extract botanical formulations for S. avenae control. Open questions include the stability of synergistic interactions under varying environmental conditions and the potential for formulation additives to further enhance synergistic effects.

Acknowledgement

AcknowledgementsThe Giza Research Center for Agricultural Innovation provided field and laboratory facilities. M.A.R. and H.E.S. designed the research; A.M. conducted field operations; International Journal of Agriculture and Food Science https://www.agriculturaljournals.com D.H. performed statistical analysis. Funded by the Egyptian Science, Technology and Innovation Funding Authority.

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