Isaac, it sounds like some good conditions for the beetles...and even though it's in full sun if the sun's behind clouds, well, I guess that kind of negates the impact of location in full sunlight. I'm probably a bit out there with this but I tend to think the beetles "sense" the micro-climate surrounding the bee hives and pass judgement on whether it is a good place "to raise their kids" or not. My hives are in full sun on probably ~2' of sandy loam, too, though it seems to drain fairly readily. My beetle population has been somewhat low, no major infestatations...yet.
I'm trying to take a three-fold approach to the beetles. Top, in-hive, and bottom. I've sat one hive aside as a "test hive". I've sat the prototype of the ISOT beneath a colony that I cut out last summer. I just put it into service yesterday when I added the mineral oil and nailed on an "awning" over the entrance to help with rain blowing into the tray. I'm hoping that the awning will also help to redirect the beetles to the sides of the opening and down to the porch/bottom level for entry rather than them simply entering by around the upper edge of the front entrance. I hope the other hives don't get jealous over the extra "bling" that this colony's getting.
The beetle's *may* be able to enter the hive through the small gap between the tray and bottom board but they will have to keep out of the oil tray...entering the front of the hive the extra modification of the metal flashing and slits will offer the beetles a nice dark refuge from the harassing bees.
Inside the hives I have Beetle Jail Juniors. I'm seeing that the bees do seem to herd the beetles to the sides of the hive where (for now) not much storage actiivity is happening...but, they are found elsewhere, too. I like to keep a trap close to the escape/feeder holes in the inner cover. I will use 2-3 traps per hive...filled with mineral oil...vegetable oil seems to go rancid too quickly and attracts ants like crazy, too. The FAMILY DOLLAR STORE has a pint of mineral oil for $2 down here...best price that I've seen, but I'd love to find it cheaper. I use it in the trays and in the Beetle Jails.
Topside is where I feel that my protection is the weakest. I'm using telescoping covers on most of my hives and on the "bling" hive. Our neighbors "down yonder"
in Australia have been using the equivalent of Handi-Wipes...those tough reusable but disposable wipes people use for dishes, countertops, etc,. Some of the Aussies are using them in-hive, but some bees also get tangled in the "fuzz" that traps the beetles by tangling up their barbed legs. Some put them in cd cases, some on top of inner covers. I'm going the last route for now...on top of the inner cover. My escape/feeder holes are screened with #8 so bees can't get too the Handi-Wipes and get tangled in them. I haven't caught any beetles in mine yet, but I haven't seen a high number of beetles nor any on top of the inner cover since installing the wipes so the jury is still out on this tactic for me. I got my copycat Handi-Wipes at "The Dollar Tree"...eight "Buddy Wipes" for $1...one wipe should work per inner cover.
Well, that's my tactics for the time being...time will tell have effective they are.
Could you post of picture of your oil tray trap? I'd like to see how you made it...I'm always looking for different designs...the simpler the better!
Best wishes,
Ed