Comparative field and laboratory efficacy of botanical and mineral-based treatments against Artona chorista in large cardamom in eastern Nepal

Abstract

Large cardamom ( Amomum subulatum Roxb.) is an economically important cash crop of the eastern Himalayas; however, its productivity is severely constrained by the leaf-eating caterpillar Artona chorista , a major defoliating pest in cardamom-growing regions of Nepal. Although non-synthetic treatments are increasingly encouraged in organic and low-residue production systems, comparative evidence linking field efficacy with laboratory toxicity under a unified experimental framework remains limited. This study evaluated four botanical, mineral-based, and traditional treatments, namely neem oil, mineral oil, titepati ( Artemisia vulgaris ) oil, and cow-dung urine, against A. chorista in Taplejung district, Nepal, using a randomized complete block design in the field and a completely randomized design in parallel laboratory bioassays. Under field conditions, neem oil (2.5 mL L⁻¹) gave the greatest reduction in larval population relative to the pre-treatment baseline (98.1%), followed by mineral oil (86.3%), titepati oil (79.6%), and cow-dung urine (65.5%); at the final observation the four treatments differed significantly from the untreated control but not from one another. In the laboratory bioassay, mineral oil caused the highest larval mortality (98.5% raw; 98.3% after Abbott correction), whereas neem oil ranked second (87.5% raw; 86.1% corrected). This reversal between settings may reflect differences in known modes of action and exposure conditions: neem effects can develop through feeding over time, whereas mineral oil relies more strongly on direct contact under controlled exposure. Neem oil gave the numerically strongest field suppression of A. chorista , while mineral oil may warrant further evaluation for situations requiring rapid knockdown with good spray coverage. The combined field-laboratory approach helps explain why field and laboratory efficacy rankings differ and supports more cautious, mechanistically informed pest-management guidance for large cardamom.