Maybe those are two varieties that hold onto their buds even with a thrip infestation. I remember Charlie saying Byron Metts was one that did that, and on the white bloom you could see tons of the little jerks running around.
LMAO ! I feel your pain , I have bought probably every pesticide to kill all hibiscus pest then here somes along thrips !!! I have spinosad , neem oill III, bayer rose and flower, and horticultural oil.
So far the hort oil is my favorite I have not seen any aphids.