Effects of Novaluron Exposure on the Oviposition and Expression of Ovarian Development Related Genes in Silkworm, Bombyx mori (Lepidoptera: Bombycidae)

<i>Bombyx mori</i> (Lepidoptera: Bombycidae) is an important economic insect, which mainly feeds on mulberry leaves and is widely used in many research fields. The growth and development of silkworm larvae are easily affected by the use of chemical insecticides such as novaluron, a benzoylurea insecticide. However, the effect of novaluron exposure on the reproduction of silkworms has not yet been studied. In this study, the effect of trace novaluron on the oviposition of silkworms and histopathological changes were first evaluated, and then the gene expression level changes after novaluron exposure were also determined by employing qRT-PCR. It was found that the number of eggs and the hatching rate of eggs in silkworms decreased significantly after feeding on leaves with a trace amount of novaluron (<i>p</i> ≤ 0.01). Furthermore, novaluron exposure could affect the development of ovary tissue by reducing the number of oocytes and oogonia in the ovaries of silkworms fed with novaluron. In addition, the transcription levels of genes related to ovary development (<i>Vg</i>, <i>Ovo</i>, <i>Otu</i>, <i>Sxl-S</i> and <i>Sxl-L</i>) and hormone regulation (<i>EcR</i> and <i>JHBP</i>2) showed varying degrees of downregulation at 24 h, 48 h, and 72 h after novaluron treatment (<i>p</i> ≤ 0.05). Therefore, we speculated that novaluron can affect the energy metabolism, ovary development, and egg formation of silkworms, thus leading to reproductive disorders of silkworms after novaluron exposure.