The following will get you part way there.

Step 1: Look up names of the organisms in your blast result. (following work with the small snippet example above)

awk -F '>|_' '/^>/ {print $2"_"$3}' test | xargs -n 1 sh -c 'efetch -db nuccore -id "$0" -format docsum | xtract -pattern DocumentSummary -element Caption,Organism' > names.txt

names.txt now contains the names of the organisms.

Step 2: Use one of the solutions in Renaming fasta headers according to a matching name list to do the replacements. There is small issue though. names.txt does not contain the version number for the accession so the solutions may need to be changed to suit your needs.