Why would this insect pest poster in Taiwan have phonetic characters (Zhuyin) on every Chinese character?
Texts written for schoolchildren will be annotated with phonetic symbols. The last sentence indicates that this poster is made for schoolchildren:

如果發現了，趁著沒孵化之前通知老師來移除。
If any [eggs] are found, take the opportunity to let the teacher know, so that they can remove [the eggs] before they hatch.