Question

What is the cartoonist's purpose in this cartoon?

to convince people that fungal bands are dangerous for beetles
to convince people that beetles are damaging to trees
to make people laugh at a play on words
to make people believe that longhorn beetles hate fungi

Answer 1

The answer is To make people laugh at a play on words.

The cartoon doesn't actually show how fungi eliminates longhorn beetles, or indicates substantial danger for the beetle. Instead, it shows the beetle's (Beatles?) annoyance about the racket the fungi "Fun Guys" are making.

Answer 2

The cartoonist's purpose in this cartoon is to make people laugh at a play on words.

While the cartoon is based on the idea that fungal bands are an effective method for the biological control of Asian longhorn beetles, the main aim of the cartoonist is to protray that idea in a comical way, depiting how these fungi actually form a music band called "the fun guys" (fungal/fun gal - fungis) and they eliminate the beetles by playing their music, that awful racket as the beetle says.