From an old MSDS sheet , if bees are particularly sensitive to pesticide levels , you would expect fast and serious research into longterm low level exposure , how the hell did this take so long to come to light.
Acute Oral LD50 (rat): 609 mg/kg
Acute Dermal LD50 (rabbit) : >2,000 mg/kg
Eye Irritation (rabbit): Non-irritating
Skin Irritation (rabbit): Slight irritant
Inhalation LC50 (female rat): 3.18 mg/L (4 hr).
Skin Sensitization (guinea pig): Not a sensitizer
Carcinogenic Potential: None listed in OSHA, NTP, ACGIH, or IARC.
Target Organs: None listed.
This pesticide is highly toxic to birds and aquatic invertebrates. For terrestrial uses, do not apply directly to water, or to areas where surface water is present or to inter-tidal areas below the mean high water mark.
Imidacloprid is highly toxic to bees if used as a foliar application, especially during flowering, but is not considered a hazard to bees when used as a seed treatment