"Dawa ya wadudu"
From Arabic دَوَاء (dawāʾ).
dawa (n class, plural dawa) or dawa (ma class, plural madawa)
In its strictest sense, this word means "medicine", but is used generally for anything that improves or protects the condition of another thing; for example dawa ya viatu (“dawa of the shoes”) means "shoe polish".
From Wiktionary: https://en.wiktionary.org/wiki/dawa
Note: So, for insects the meaning of "medicine" or "improving protection" is not applied. ;)
I think the Arabic etimology can explain better this meaning:
From the root د و ي (d-w-y); compare دَوًى (dawan, “disease”), دَاوَى (dāwā, “to treat a disease”).
دَوَاء • (dawāʾ) m (plural أَدْوِيَة (ʾadwiya))
1) (medicine) remedy, medicine, medication, drug
From Wiktionary: https://en.wiktionary.org/wiki/%D8%AF%D9%88%D8%A7%D8%A1#Arabic
(So, perhaps the meaning for this phrase would be "Drug of insects" or "Drug for insects) =)