My August 2016 Understanding of Neonicotinoids -- are we killing bees?
I won't cite any of the hundreds of published studies on this subject. Just search scholar.google.com for "neonicotinoid bee", if you like.
Dinotefuran, imidacloprid, thiamethoxam, and clothianidin are neonicotinoid insecticides, sometimes called "neonics." Each of these is marketed under many brand names. FTT members are familiar with various brands of imidacloprid used to prevent aphid infestation.
Background
Nicotine is a neurotoxin. Some insects (as well as humans) are capable of detoxifying nicotine (chemically breaking it down to non-toxic components). Tweaking the chemical structure of nicotine can prevent its detoxification. These "new" versions of nicotine-like compounds are known as neonicotinoids.
The Good
Some crops simply cannot be grown profitably without the use of some insecticide. Neonicotinoids are remarkably effective at minimizing the potential damage caused by a wide spectrum of insect herbivores. Neonicotinoids are used in a way that renders all parts of the plant toxic to insects.
The Bad
Neonicotinoids kill a wide spectrum of insects, including many that would not cause damage, such as those that pollinate crops--wild bees and honeybees. There is no question about this effect. Not only are leaves and roots rendered toxic, the pollen is toxic as well.
The Ugly
Crops that must be pollinated by insects will injure pollinators that forage on them if neonicotinoids are used. A recent study of oil seed rape (used to produce Canola, for example) clearly demonstrates that use of neonicotinoids on this crop reduces local bee populations. This likely applies to most commercial vegetable crops.
For crops that are treated with neonicotinoids in powdered or granular form applied at planting or later (regardless of whether or not the crops must be pollinated), the insecticide is aerosolized and dispersed into the air.
The Not So Ugly
Although neonicotinoids applied in liquid form in transplant water will still render all parts of the plant (including the pollen) toxic to insects for much of the growing season, it is a significant hazard to bees only if the blossoms are exposed. With tobacco in particular, topping the plants (removing the blossom head) or bagging the head minimizes the risk to pollinators. This is the possible because tobacco is self-fertile.
Conclusion
If you use Admire (imidacloprid, which is also sold under a number of other brand names) to prevent aphids, apply it as a liquid to transplant water, and top the plants or bag them. Don't use it on Orientals, for example, that are allowed to blossom in open air.
Bob