Krüppel-homolog 1 is critical for larval metamorphosis in an herbivorous ladybird

Two transcriptional repressors Krüppel-homolog 1 (Kr-h1) and Hairy have been confirmed mediating juvenile hormone (JH) signaling in Dipterans. To date, nevertheless, whether the two repressors transduce the JH signal has not been explored in any Coleopteran species. Here we found that HvKr-h1 exhibited a temporal expression pattern opposite to that of HvHairy in Henosepilachna vigintioctomaculata, an herbivorous ladybird mainly damaging potato. Moreover, HvKr-h1 showed opposite expression profiles to that of HvHairy in the larval fore and hindguts. RNA interference (RNAi) against Kr-h1 at the second larval instar stage caused premature pupae and adults, and abnormal prepupae. Knockdown of HvKr-h1 at the third and fourth (final) larval instar stages led to deformed prepupae and misshapen pupae; the phenotypic defects were more severe when injection of dsRNA at the final instar stage. Moreover, RNAi for HvKr-h1 disrupted JH and 20E signaling, indicating by abnormal expression levels of JH signaling pathway genes (Met, Tai, Hairy, Groucho) and upregulated BrC and E93. Conversely, depletion of either HvHairy or HvGroucho did not affect larval developing. Both dsHairy- or dsGroucho-treated and control larvae exhibited steady weight gain and normal transitions through the third and fourth instars, prepupal, and pupal stages. It appears that Kr-h1, rather than Hairy/Groucho, exerts an anti-metamorphic role during larva developing in H. vigintioctomaculata.