If you have black spots on the stems also it is a disease called "Lasiodiplodia Canker" which will cause black sunken spots or sunken areas on Aucuba stems. Dieback of foliage results.

Most likely it is simple sunburn from the heat and low humidity. Although aucubas will tolerate direct sun they really do prefer to be in part to full shade. Cut the dying leaves off and water regularly and it should heal just fine on it's own.

After all, we usually don't have drought like this for as long as it has gone on and as hot as it has been. I recently transplanted a 4' tall Aucuba and let me tell you,,,, it has taken quite of bit of pampering to keep it looking good and it's in full shade.

I thought it might be due to the weather. That makes sense and I hope that's all it is. I have it in my yard as well in partial shade and no problems, and I haven't been here that long but the Aucuba has. Thank you -
dug