Precocious Downregulation of Krüppel-Homolog 1 in the Migratory Locust, Locusta migratoria, Gives Rise to An Adultoid Phenotype with Accelerated Ovarian Development but Disturbed Mating and Oviposition

Abstract

Krüppel-homolog 1 (Kr-h1) is a zinc finger transcription factor maintaining the status quo in immature insect stages and promoting reproduction in adult insects through the transduction of the Juvenile Hormone (JH) signal. Knockdown studies have shown that precocious silencing of <i>Kr-h1</i> in the immature stages results in the premature development of adult features. However, the molecular characteristics and reproductive potential of these premature adult insect stages are still poorly understood. Here we report on an adult-like or 'adultoid' phenotype of the migratory locust, <i>Locusta migratoria</i>, obtained after a premature metamorphosis induced by the silencing of <i>LmKr-h1</i> in the penultimate instar. The freshly molted adultoid shows precocious development of adult features, corresponding with increased transcript levels of the adult specifier gene <i>LmE93</i>. Furthermore, accelerated ovarian maturation and vitellogenesis were observed in female adultoids, coinciding with elevated expression of <i>LmCYP15A1</i> in <i>corpora allata</i> (CA) and <i>LmKr-h1</i> and <i>vitellogenin</i> genes (<i>LmVg</i>) in fat body, whereas <i>LmE93</i> and <i>Methoprene-tolerant</i> (<i>LmMet</i>) transcript levels decreased in fat body. In adultoid ovaries, expression of the <i>Halloween</i> genes, <i>Spook</i> (<i>LmSpo</i>) and <i>Phantom</i> (<i>LmPhm</i>), was elevated as well. In addition, the processes of mating and oviposition were severely disturbed in these females. <i>L. migratoria</i> is a well-known, swarm-forming pest insect that can destroy crops and harvests in some of the world's poorest countries. As such, a better understanding of factors that are capable of significantly reducing the reproductive potential of this pest may be of crucial importance for the development of novel locust control strategies.