This is in reference to using 1 image in place of multiple images, to reduce the number of requests made by the server. (More info here: https://css-tricks.com/css-sprites/)
According to your report, the images that could be optimized/combined are:
https://www.insect.gr/wp-content/plugins/wp-google-places-review-slider/admin/partials/google_mystery_man.png
https://www.insect.gr/wp-content/plugins/wp-google-places-review-slider/public/partials/imgs/stars_5_yellow.png
https://www.insect.gr/wp-content/themes/anona/images/top_arrow.png
https://www.insect.gr/wp-content/uploads/revslider/anona-slider-2017/ant-icon.png
https://www.insect.gr/wp-content/uploads/revslider/anona-slider-2017/cockroach-icon.png
https://www.insect.gr/wp-content/uploads/revslider/anona-slider-2017/mosquito-icon.png
https://www.insect.gr/wp-content/uploads/revslider/anona-slider-2017/rat-icon.png
In this case, I wouldn’t worry about that aspect since 1 group of images (google_mystery_man.png, stars_5_yellow.png) is part of a plugin (WP Google Review Slider), and another group includes images inserted into a slider template.
If you wanted to pursue perfection, you could reach out to the plugin author of WP Google Review Slider and ask that they combine the 2 images used in their plugin into a sprite. (https://www.ads-software.com/support/plugin/wp-google-places-review-slider/)
Then you could create a sprite for the 4 images shown in your homepage slider (ant-icon.png, cockroach-icon.png, mosquito-icon.png, rat-icon.png), and then reference the sprite with some custom HTML elements to display those in your slider.
Here are some great resources for creating sprites from your images:
https://spritegen.website-performance.org/
https://www.spritecow.com/
You may also want to review this related topic:
https://www.ads-software.com/support/topic/content-delivery-network-cdn/
