Historically, Bt maize hybrids have been produced with the Bt alleles in a hemizygous state. Homozygous Bt transgenes increase the expression of Bt proteins in plants; however, recent studies have only briefly explored the zygosity of Bt transgenes in maize hybrids and its effects on the control of lepidopteran pests. In this study, we investigated whether an additional allelic dose of the single Bt events Bt11 and MIR162, and a pyramided version (Bt11 + MIR162 + GA21) would impact Bt protein expression in leaves and increase the control of fall armyworm, Spodoptera frugiperda, in leaves and grains of near-isogenic maize hybrids. Our results revealed that homozygous Bt hybrids had higher Cry1Ab and Vip3Aa20 protein concentrations in leaves than their hemizygous versions. However, higher concentrations of Bt proteins in homozygous versions did not increase the control of S. frugiperda. Hybrids expressing Cry1Ab, hemizygous and homozygous for the transgene, had similar mortality of S. frugiperda fed on leaves and grains as the non-Bt near-isogenic version, likely due to resistance of the pest to Cry1Ab. High susceptibility to Vip3Aa20 caused all larvae to die on hemizygous and homozygous MIR162 leaves. Also, larvae that survived on Vip3Aa20 grains did not gain weight after four days of feeding, regardless of the Bt zygosity of Vip3Aa20-expressing grains. Additional implications of Bt zygosity in maize hybrids on insect resistance management strategies are discussed.

从历史上看，Bt玉米杂种是用半合子状态的Bt等位基因生产的。纯合Bt转基因增加植物中Bt蛋白的表达；然而，最近的研究仅简要地探讨了玉米杂种中Bt转基因的合子性及其对鳞翅目害虫的控制作用。在这项研究中，我们调查了单次Bt事件Bt11和MIR162以及金字塔形式（Bt11 + MIR162 + GA21）的额外等位基因剂量是否会影响叶片中Bt蛋白的表达并增强对秋天粘虫Spodoptera frugiperda的控制在近等基因玉米杂交种的叶片和谷粒中。我们的研究结果表明，纯合子Bt杂种的叶片中Cry1Ab和Vip3Aa20蛋白浓度高于半合子。但是，纯合体形式中较高浓度的Bt蛋白不会增加对S. frugiperda的控制。表达Cry1Ab，半合子和纯合子为转基因的杂种具有相似的S. frugiperda死亡率以非Bt近等基因形式的叶片和谷类为食，这可能是由于害虫对Cry1Ab的抗性所致。对Vip3Aa20的高度敏感性导致所有幼虫在半合和纯合MIR162叶片上死亡。同样，在Vip3Aa20谷粒中存活的幼虫在饲喂四天后仍未增加体重，无论表​​达Vip3Aa20谷粒的Bt合子性如何。讨论了Bt合子性在玉米杂交种中的抗虫性管理策略。