The Potential of Parapanteles hyposidrae and Protapanteles immunis (Hymenoptera: Braconidae) as Biocontrol Agents for the Tea Grey Geometrid Ectropis grisescens (Lepidoptera)

The tea grey geometrid Ectropis grisescens has long been a significant insect pest of tea plants in China. Two parasitoids, Parapanteles hyposidrae and Protapanteles immunis (Hymenoptera: Braconidae: Microgastrinae), are the most important parasitoids in the larval stage of E. grisescens. Yet, the potential of these two parasitoids for controlling the tea grey geometrid is not known. Here, we studied the parasitism performance of these two parasitoid species on different host densities under different temperatures as well as the interference effect of parasitoid density. The results showed that both parasitoid species, Pa. hyposidrae and Pr. immunis, exhibited a Type II functional response towards the tea grey geometrid E. grisescens at four tested temperatures. With increasing the density of E. grisescens larvae, the number of parasitized larvae increased until a maximum was reached. The highest number of hosts parasitized by Pa. hyposidrae or Pr. immunis reached 14.5 or 14.75 hosts d^-1 at 22 °C, respectively. The estimated values of instantaneous searching efficiency (a) and handling time (h) for Pa. hyposidrae or Pr. immunis were 1.420 or 3.621 and 0.04 or 0.053 at 22 °C, respectively. Pr. immunis performed better than Pa. hyposidrae under higher temperatures. The parasitism rate by a single female parasitoid decreased with increasing parasitoid density at different temperatures, resulting in a reduction of searching efficiency. The findings of this study showed that Pr.immunis could be a better effective biocontrol agent than Pa. hyposidrae against the tea grey geometrid.

Analysis of the Antifungal Properties of Bacillus velezensis B-4 Through a Bioassay and Complete-Genome Sequencing

The strain B-4, isolated from a field in Changsha (China), presents strong antifungal activities, as identified by the Kirby–Bauer test, especially for pathogens that harm crops. Here, we obtained the complete genome sequence of the strain B-4 by Pacific Biosciences single-molecule real-time sequencing, making it well analyzed for understanding mechanisms and creating biological agents. Its 3,919-kb circular chromosome genome has 3,725 protein-coding genes [coding sequences (CDSs)] and 46.7% guanine–cytosine content. A comparative genome analysis of B-4 with other published strains (including Bacillus velezensis, Bacillus amyloliquefaciens, and Bacillus subtilis) revealed that the strain B-4 is a B. velezensis strain. These different strains have 2,889 CDSs in common, whereas 179 CDSs were found to be unique in the strain B-4, which is a far greater number than that in other strains. Regarding the antifungal activities of B-4, we were specifically concerned with the genes involved in the biosynthesis of secondary metabolites. In total, more than 19.56% of the genome was annotated to 12 gene clusters relating to synthesis of antimicrobial metabolites, which contained various enzyme-encoding operons for non-ribosomal peptide synthetases, polyketide synthases, and lantipeptide synthesis proteins. They were all considered to be related to the production of bacteriostatic substances or stimulation of induced systemic resistance by bacterial metabolites. These situations also present an advantage over those of other strains for biocontrol potential. We provide evidence that the biological control effect of the strain B-4, as demonstrated in antibacterial activity experiments and predicted from the complete genome sequence analysis, provides the basis for research promoting agricultural research on sustainable development, especially the contribution of biotechnology to agriculture.