Comparative Transcriptome Analysis of the Effects of a Non-Insect Artificial Diet on the Nutritional Development of Harmonia axyridis

Abstract

Artificial diets applied in the mass-rearing propagation of H. axyridis can improve reproductive ability by optimizing the feeding formula. This study used transcriptome data to investigate the effects of various artificial diets on the growth and development of H. axyridis. Results indicate that spawning increased with the low-fat and JH III-supplemented artificial diet (Diet 3). Furthermore, the highest glycogen content found in Diet 3 was significantly different from the other two groups. Triglyceride content decreased as adult feeding time increased in the three artificial diet groups, with the fastest decrease observed in the low-fat diet (Diet 2). Protein content increased gradually in the high-fat diet (Diet 1) group compared to the other treatment groups. The adults reared on low-fat artificial diets, when compared to those on artificial diets supplemented with juvenile hormones at the transcriptome level, were found to have upregulated genes enriched in ubiquitin-mediated proteolysis, ribosome biogenesis, and the hedgehog signaling pathway. In contrast, the genes upregulated in the latter group were enriched in oxidative phosphorylation, amino acid biosynthesis, and the metabolism of other amino acids. The results suggest that nutritional status significantly affects the growth and development of H. axyridis and has practical implications for the artificial feeding of natural pest enemies.

Keywords: H. axyridis; artificial diet; juvenile hormone III; nutritional; transcriptome.

Figure 1

Effect of ovarian development of different artificial diets in H. axyridis. (a) Dissected ovaries five days after emergence. Diet 1 (standard, artificial), Diet 2 (low fat artificial), and Diet 3 (addition of juvenile hormone III to Diet 2). (b) ovarian length and ovarian width. The scale bar represents 1 mm. Different letters above each bar indicate significant differences among different treatments using One-way ANOVA test (p < 0.05).

Figure 2

Protein, glycogen, and triglyceride content during the female adult stage after different artificial diets. Diet 1, Diet 2, and Diet 3 were fed on the first day of emergence. Protein, glycogen, and triglyceride contents were monitored at 0, 10, 20, 30, and 40 days of age. SPSS analyzed the significance of the differences in the nutrient content. The nutrient contents are shown as the means ± SEs and were found to be significantly different. Different letters above each bar indicate significant differences among different treatments using One-way ANOVA (p < 0.001) and Kruskal-Wallis test (p < 0.05).

Figure 3

Scatter diagrams representing the comparisons of the genome-wide expression profiles of control and treatment. Note: Each green point represents a decrease, each red point represents an increase, and each blue point represents no significant difference in gene expression.

Figure 4

Summary of the annotations of differentially expressed genes in H. axyridis. The GO classifications are shown according to involvement in biological processes, cellular components, and molecular functions.

Figure 5

The 20 most significant KEGG pathways were selected from the KEGG enrichment results. In the figure, the abscissa indicates the ratio of differential genes annotated to the KEGG pathways to the total number of such genes; the ordinate stands for the KEGG pathways. The size of the points represents the number of genes annotated to the KEGG pathways, and the color from red to purple represents the significance level of enrichment.

Figure 6

Analysis of differentially expressed genes under different artificial diets in H. axyridis. The expression changes for each candidate gene as measured by RNA-seq and qRT-PCR.