Anyone seeing unusual fall dwindling in the bees? Several local operations are seeing this and are looking for a cause. What is seen is the gradual decline of populations in the beeyards with scattered dead bees around the hives and some bees dying with poisoning-like symptoms (tongues out and partial paralysis). This seems to affect large numbers of hives simultaneously with varying degrees of depopulation ranging from maybe a 20% thinning of bees to collapse down to a couple frames. It is occurring in 1000+ colonies in 30+ yards spread across 2 counties. This began to be evident in mid-September but is now clearly widespread. Here are some facts:

The bees- The bees have been on local forage, not on monoculture crops, and have not had known ag chemical exposure since spring. Behavior is normal though flight is reduced. Brood is not abundant, probably 3 frames with a 5 inch circle in hives still having 8 frames of bees. Ample frames of pollen are present in collapsing hives.
The weather- Weather is presently in the 70's with dry conditions but a good rain 3 weeks ago. There have been no heavy frosts. A two month dearth preceded the rains but bees were fed as needed.
Forage- There is limited but present starthistle, mustard bloom, etc. which is typical for the area. No strong nectar flow.
The mites- Absent with powdered sugar roles of 0-1 in 300 bee samples.
Mite treatments- Amitraz applied in the first week of September.
Feeding regimen- Sugar syrup and 1-2lb. subs every 10-14 days.

With the scope of involved hives, I suspect this is an event coming from from within the hive, possibly combined with weather conditions (fly weather, cooler nights). Possible culprits:

Disease- Some of hives exhibit IBD (snotbrood) symptoms with yellowing larvae and spotty pattern, DFW bees are very rarely seen. There is no chalkbrood. Nosema counts will be checked this week.
Poisoning- 3 miticide strengths applied in 3 different operations with the most notable symptoms in the operation using the lowest concentration.
Toxic feed- Subs are dry Beepro made following manufacturers direction with 5 gal. HFCS and 50# sugar per 50# dry mix. Canola and corn oil are added per Randy Oliver's published formula, and 2/3 cup ProHealth are added in each batch. This recipe has not been changed for several years and the only difference this year is Thymol in the new formulation of ProHealth and a new production batch of powdered Beepro. Is anyone seeing issues with these products this year?
Toxic syrup- Bees fed only Dryvert, in top feeders, for their sugar source seem to be faring better but are not great. Syrup is 1.2:1 to 1.8:1 sugar mix or thinned HFCS depending on the operation. Sugar is C&H granulated cane sugar. Syrup is not fermented and has no additives.

If anyone has seen similar findings, your input would be appreciated.