Hi mohana, Being I am in central NY, I have to bring my Hibiscus inside for the fall and winter. It is normal for these to drop their leaves whenever they are moved. They are sensitive. Ive had leaf drop just by rotating the container around. As for the Aphids, on your next sunny day take the plant outside and hose it off thoroughly making sure to get the undersides of the leaves. Use a strong as stream of water as possible without damaging the leaves. Once dry, I like to apply insecticidal soap also making sure to get the underside of the leaves. That should take care on any left over Aphids. You may have to repeat this process a couple of times.This is due to any eggs that may have been missed.Good luck.

I have no idea what temperatures you had the plant in--indside your home--but when you removed it to the great outdoors, what kind of temperature change did the plant suffer.

Generally, hibs can take temperatures down into the forties...maybe the high thirties, without experiencing any harm....as long as the wind doesn't have any effect.

The aphids were outside...or they were in the soil of the plant where they came from eggs, to larvae, to adult stages before they emerged to feed on your plant.

You can try this method: Take the plant to your garage or shed, there to cover it entirely with a plastic sheet.
Uncover a corner, and into it spray an insecticide specifically to treat aphids (and other bugs). Spray to cover all surfaces...top and bottom.
Fold close the corner. Wait 24 hours before examining the plant. If you see no sign of bugs, then you might feel its safe to take indoors. But always keep vigil.
In seven days, repeat the spray method....and in seven days, repeat the spray method. 3 sprays in 21 days should break any cycle the bugs might be going through.

Instead of spraying, try the water method:
Generally, if you can see the aphids, they can be lifted off and disposed of. Then spray hard with a hand sprayer or a hose to knock the bugs off the plant. Do cover all surfaces. The bugs cannot climb back up.

With a 2 1/2" soap/water solution.....that's 1 part soap to 40 parts water. In Canada, a quart has 40 oz....in the States...32 oz.
In America, use 3/4 of an oz and 32 oz of water to give you such solution. Spray the plant top to bottom, bottom to top, with the solution; wait 10 minutes, then rinse with warmish water covering all surfaces...top to bottom bottom to top. This will generally kill any and all bugs the soap hits.
Repeat this in 7 days....then again in 7 days.
This should break the cycle of eggs, to larvae, to adult.

If you feel the 2 1/2% solution is too strong, then cut back....1 tablespoon soap(1/2 oz) will half that)

Being in Georgia you could probably let it defoliate without much stress. Wrap the pot in bubble wrap then black plastic as insulation, be sure to leave drainage. Leave it outside and let it go dormant. Then when it starts to show signs of new growth, tip prune the top stems, then feed and water it. It will come back great. You can then treat the aphids which survived the winter with a dunk or systemic.

Hibiscus are very prone to pests indoors. If it's not aphids, it's whiteflies or mites. If you're going to keep one inside, expect to have to spray periodically with something. I personally gave up - it wasn't worth the aggravation, even though I love the plants. If I want a new one, I'll buy it in the spring.

Even a healthy hibiscus will drop spent flowers and leaves on the floor. They are messy plants by nature. So if the husband is a neat freak, he's never going to be happy with it.

That said, if you're going to keep this plant, putting it outside to freeze the bugs won't work. If it's cold enough to freeze the bugs, it will be cold enough to injure or kill the plant too. And the sudden cold is a serious shock to the plant, which causes it to drop leaves. Then it has to grow new ones, which causes it to use up much of its reserved energy, thus making it weaker and even more susceptible to pests until it can go out in the bright sun again to recover in the spring.

Aphids tend to cluster on flowers and flower buds. So first task is to cut off (horrors, yes, I said cut off) any flowers and buds on which you see aphids and dispose of them in a sealed bag in your outdoor trash.

Next, choose an appropriate pesticide. A fungicide will not work on pests, it treats fungal diseases. Read the label (if you're in the store, peel it open to read the inside part, it's allowed!). The pesticide must specifically say that it treats aphids. If you're going to spray indoors, it must also say that it is safe to spray indoors on houseplants. I recommend insecticidal soap or neem oil.

If you have a warmish day where you can haul the plant outdoors to spray, you can use an outdoor spray, just be sure the plant is totally dry before it comes back inside and will stay warm enough until then. If you're spraying outside, I highly recommend Bayer Rose & Flower Spray. Unfortunately, it is not safe to spray indoors.

The label will also tell you how frequently to spray. Probably something like three times 5 to 7 days apart. If you don't follow that timetable, the aphids will come back and you'll have to start all over again.

Good luck! They are gorgeous flowers!