Gene Kr-h1 regulates fecundity in predatory ladybugs

The Kr-h1 gene, linked to juvenile hormone signaling, interferes with ovarian development and egg production in females of Coccinella septempunctata. The result comes from a study by Chinese scientists. The research used RNA interference to reduce gene expression and evaluate its reproductive effects on the predator, used in the biological control of aphids and other arthropod pests.

The team observed a 28,74 percent drop in average egg production after Kr-h1 silencing. Females injected with Kr-h1-dsRNA produced 119 eggs per female in twenty days. In the control group without injection, the average reached 167 eggs per female. In the group treated with GFP-dsRNA, used as a control for the technique, the average reached 168 eggs per female.

Central role

The study indicates a central role for Kr-h1 in the fertility of Coccinella septempunctataThe gene encodes the Krüppel homolog 1 transcription factor. The protein acts in the juvenile hormone pathway, known for regulating growth, metamorphosis, and reproduction in insects.

The researchers also tested the gene's response to juvenile hormone in an artificial diet. Females fed a diet containing juvenile hormone showed higher Kr-h1 expression at five and ten days, compared to females maintained on a diet without the hormone. At five days, expression was 3,02 times higher. At ten days, it was 1,76 times higher.

The experiment reinforces the relationship between juvenile hormone and Kr-h1 transcription in Coccinella septempunctataAccording to scientists, this response helps explain previous effects of hormone supplementation on the species' reproduction. In a study cited in the article, an artificial diet with juvenile hormone increased egg production fourfold compared to a diet without supplementation.

Gene function

To evaluate gene function, researchers injected newly emerged females with one microliter of Kr-h1-dsRNA at a concentration of 4500 nanograms per microliter. The injection was administered into the intersegmental membrane between the third and fourth abdominal segments. The control group received GFP-dsRNA. Each treatment involved 50 females, with three replicates.

The interference reduced Kr-h1 expression compared to the GFP-dsRNA control. The decrease reached 30,97 percent five days after injection and 38,32 percent ten days after injection. The reduction in expression was accompanied by delayed ovarian development.

Images and measurements

Images and measurements of the ovaries showed less reproductive advancement in the group treated with Kr-h1-dsRNA. At five days, the ovaries had fewer mature eggs. The ovarioles also exhibited a shrunken appearance. Measurements of ovarian length, length and width of the left and right ovarian chambers decreased compared to the GFP-dsRNA group.

At ten days, researchers recorded an increase in some dimensions of the ovaries in the Kr-h1-dsRNA group compared to the GFP-dsRNA control. Even so, the treated females presented more empty ovarioles. This pattern suggests impairment in the reproductive process, despite the partial recovery of gene expression over time.

Scientists point to a possible gradual reduction in the efficiency of RNA interference. The injected Kr-h1-dsRNA may undergo degradation by cellular nucleases. As a result, Kr-h1 expression may recover some activity after a few days.

Coccinella septempunctata It occupies an important position in biological control programs. The predatory species attacks aphids, whiteflies, leafhoppers, and mites. Therefore, understanding its reproductive regulation can support improvements in artificial diets and mass rearing systems.

The study also provides a basis for research on hormonal pathways in insects. The juvenile hormone-Met-Kr-h1 pathway participates in vitellogenesis, ovarian development, and fecundity in different species. In Coccinella septempunctataThe data indicate a direct involvement of Kr-h1 in egg production and ovarian development.

Further information at doi.org/10.3390/insects17060577