Although experts are stumped about what's causing the colony-collapse disorder die-off in U.S. commercial beehives, there is some speculation that Arizona's famed Africanized or "killer bee" wild-bee population is somehow immune.Dee Lusby's bees are doing fine. Actually, they're doing better than that, says the owner of Lusby Apiaries & Arizona Rangeland Honey of Arivaca.Lusby has 900 hives of "free range" organic bees spread out over ranches from Benson to Sasabe."I've only lost one or two, maybe three (hives) out of every 30 or 40 hives," said Lusby.She's not surprised by her good fortune or the modern commercial beekeepers' hive-mortality rates.Lusby has a hunch the disorder is the result of a number of factors, including the use of pesticides, bee-growth formulas, artificial food supplements, breeding for size, inbreeding all or some of which may make them susceptible to mites, viruses and fungi and maybe even some strange side effects from feeding on genetically modified crops.Breeding for size is a major factor, Lusby believes. She says the commercial honeybees are now too large to feed on some of the very plants that historically may have given them immunity to diseases and parasites. They're simply too big to get into those plant's flowers, she says.And the man who takes the bees out of Bisbee, Reed "The Killer Bee Guy" Booth, says he's not surprised Africanized bees are thriving.Booth started out with beekeeping to make retail honey and honey mustard, and branched out to do bee removals after the Africanized bees invaded Arizona in the early 1990s. He says he gets one to five eradication calls a day from around Cochise County during warm weather."It's going to be a banner year for bees," he says."The Africanized bees are somewhat more resistant" than the European honeybees, he says of the aggressive, slightly smaller wild bees that produce bumper crops of honey and bad press. "But they're somewhat resistant to anything, probably including nuclear war."Booth says he switched from European bees to wild Africanized bees not long after they spread through Arizona."I used to have two sets of hives," says Booth. "But I got tired of going down and either finding my European bees Africanized or dead. I gave up, so, Killer Bee Honey."But Gloria DeGrandi-Hoffman, research leader of the USDA's Carl Hayden Bee Research Center in Tucson, is not so quick to crown the wildly enthusiastic Africanized honeybees as superior."We don't push the African populations like we do Europeans," DeGrandi-Hoffman said of the carefully genetically controlled honeybees used by commercial beekeepers for field work."We're putting them on trucks and taking them halfway across the country. We're stressing them in almost a feedlot situation, feeding them protein supplements. We're stressing them pretty good. And that doesn't happen with Africans."