Department of Entomology, Louisiana State University-Agricultural Center, Baton Rouge, LA 70803-0001, USA.
Pest Manag Sci. 2013 Feb;69(2):250-6. doi: 10.1002/ps.3382. Epub 2012 Aug 28.
Feeding assays using adult rice water weevils and foliage of plants treated as seeds with chlorantraniliprole and thiamethoxam at different rates were conducted to evaluate the systemic adulticidal and feeding effects. Dose-mortality relationships were determined for thiamethoxam seed treatments by combining leaf area lost due to feeding and insecticide residues analyzed by LC/MS/MS. Changes in adulticidal activity of thiamethoxam were also investigated by contrasting adult mortalities at the 5-6-leaf and tillering stages of rice.
Adult weevil mortalities and leaf consumption rates on foliage were affected in thiamethoxam but not in chlorantraniliprole treatments when rice was at the 6-7-leaf stage. The LD(50) for weevils feeding on thiamethoxam-treated rice at the 2-3-leaf stage was 447 pg insecticide weevil(-1) (95% CL: 25-830 pg weevil(-1)) but was lower (142 pg weevil(-1); 95% CL: 102-180 pg weevil(-1)) in experiments with 3-4-leaf-stage plants. Mortalities on leaves from 5-6-leaf-stage plants were consistently higher than on leaves from tillering plants. Thiamethoxam residues measured by ELISA increased with seed treatment rate and differed between plant stages.
The LD(50) values developed in this study are the first values for leaf-feeding insects on foliage of plants treated as seeds with thiamethoxam. The attrition of adulticidal activity of thiamethoxam in foliage of older plants may help to explain the reduced effectiveness of seed treatments against rice water larvae that is seen at later stages of rice growth in field studies. The differential activity of these two seed treatments on adults suggests that adult mortality contributes to the field efficacy of thiamethoxam but not to that of chlorantraniliprole.
使用成年稻水象甲和用氯虫苯甲酰胺和噻虫嗪以不同剂量处理的种子处理的叶片进行喂养试验，以评估系统的成虫杀灭和取食作用。噻虫嗪种子处理的剂量 - 死亡率关系是通过结合因取食和用 LC/MS/MS 分析的杀虫剂残留而损失的叶面积来确定的。还通过对比水稻 5-6 叶期和分蘖期的成虫死亡率来研究噻虫嗪成虫杀灭活性的变化。
当水稻处于 6-7 叶期时，噻虫嗪处理的叶片上的成年象甲死亡率和叶片消耗率受到影响，但氯虫苯甲酰胺处理则没有。在 2-3 叶期，以噻虫嗪处理的水稻为食的象甲的 LD50 为 447 pg 杀虫剂象甲(-1)（95%置信区间：25-830 pg 象甲(-1)），但在 3-4 叶期的试验中，LD50 较低（142 pg 象甲(-1)；95%置信区间：102-180 pg 象甲(-1)）。来自 5-6 叶期植株的叶片上的死亡率始终高于来自分蘖期植株的叶片。通过 ELISA 测量的噻虫嗪残留量随种子处理率的增加而增加，并且在不同的植物阶段之间存在差异。
本研究中开发的 LD50 值是在以噻虫嗪处理的种子的叶片上以叶为食的昆虫的第一个值。在较老植株的叶片中噻虫嗪成虫杀灭活性的损耗可能有助于解释在田间研究中，在水稻生长的后期阶段，种子处理对稻水象幼虫的效果降低的原因。这两种种子处理对成虫的不同活性表明，成虫死亡率有助于噻虫嗪的田间功效，但对氯虫苯甲酰胺的田间功效没有影响。
