Allyl isothiocyanate as a fumigant in the cowpea and its effect on the physical properties of the grain

ABSTRACT The cowpea is subject to both quantitative and qualitative loss during storage due to attack by the insect pest Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae). There is a growing interest in controlling the pest using insecticides that result from the reactions of secondary metabolites produced by plants, due to their high efficiency, wide availability and selectivity for the target organisms. The present study aimed to evaluate the fumigant activity of allyl isothiocyanate (AITC) on the development of C. maculatus and its effect on the physical properties of the cowpea. To evaluate the instantaneous population growth rate (ri), the insects were exposed to concentrations of 3.81, 5.71, 7.67, 9.41 and 17.85 mL AITC m-3 cowpea (corresponding to LC1, LC10, LC30, LC50 and LC95) for 40 days, after which the physical properties of the cowpea were analyzed. The degree of infestation increased considerably with the reduction in AITC concentration, as did the water content and electrical conductivity. The germination percentage and apparent density decreased with the reduction in AITC concentration. The LC10 sublethal concentration reduced reproduction in C. maculatus and the degree of infestation of the cowpea after 40 days of storage. AITC inhibits the development of C. maculatus and helps maintain the physical properties of the cowpea, thereby representing an alternative to the use of traditional insecticides and showing potential for the control of insect pests in stored grain.

摘要 豇豆在贮藏过程中会因四纹豆象（Callosobruchus maculatus (Fabricius)，鞘翅目：叶甲科）的侵害而同时遭受数量与品质损失。目前，利用植物次生代谢产物衍生的杀虫剂防控该害虫的研究愈发受到重视，这类药剂具备高效、易得且对靶标生物选择性强的优势。本研究旨在评估异硫氰酸烯丙酯（allyl isothiocyanate，AITC）对四纹豆象生长发育的熏蒸活性，及其对豇豆物理特性的影响。为测定瞬时种群增长率（ri），将试虫暴露于3.81、5.71、7.67、9.41及17.85 mL·m⁻³豇豆体积的AITC浓度（分别对应LC1、LC10、LC30、LC50及LC95）中，处理周期为40天，随后对豇豆的物理特性开展分析。结果显示，随着AITC浓度降低，豇豆受侵染程度显著提升，籽粒含水量与电导率亦呈相同变化趋势；而发芽率与表观密度则随AITC浓度降低而下降。LC10亚致死浓度可抑制四纹豆象的繁殖，并降低贮藏40天后豇豆的受侵染程度。异硫氰酸烯丙酯（AITC）可抑制四纹豆象的生长发育，同时有助于维持豇豆的物理特性，因此可作为传统杀虫剂的替代方案，在储粮害虫防控领域具备应用潜力。