Using video-tracking to assess sublethal effects of pesticides on honey bees (apis mellifera l.)

Abstract - Concern about the role of pesticides in honey bee decline has highlighted the need to examine the effects of sublethal exposure on bee behaviors. The video-tracking system EthoVisionXT (Noldus Information Technologies) was used to measure the effects of sublethal exposure to tau-fluvalinate and imidacloprid on honey bee locomotion, interactions, and time spent near a food source over a 24-h observation period. Bees were either treated topically with 0.3, 1.5, and 3 mg tau-fluvalinate or exposed to 0.05, 0.5, 5.0, 50, and 500 ppb imidacloprid in a sugar agar cube. Tau-fluvalinate caused a significant reduction in distance moved at all dose levels (p<0.05), as did 50 and 500 ppb imidacloprid (p<0.001). Bees exposed to 50 and 500 ppb spent significantly more time near the food source than control bees ( p<0.05). Interaction time decreased as time in the food zone increased for both chemicals. This study documents that video-tracking of bee behavior can enhance current protocols for measuring the effects of pesticides on honey bees at sublethal levels. It may provide a means of identifying problematic compounds for further testing.

Findings of this study include:
"Neonicotinoid compounds act as agonists of nicotinic acetylcholine receptors (nAChRs) [27]. They cause persistent activation of cholinergic receptors, leading to hyperexcitation and eventual death [28]. As seen in Figure 2a, imidacloprid has a stimulatory effect on locomotor activity at the lowest level of exposure, but an opposite effect at the highest concentrations. Similar results have been documented by Lambin et al. [29], who reported increased motor activity following topical application of imidacloprid at 1.25 ng per bee but a decrease in mobility of bees treated with >5 ng per bee. The stimulatory effect may be indicative of nicotinic activation by low doses of the insecticide, whereas a nonspecific toxic effect is seen at higher doses. Although the oral LD50 of neonicotinoids is much higher than the estimated daily ingestion of a forager [30], if treated crop plants constitute the majority of a colony’s nectar and pollen resources while in bloom, multiple exposures to sublethal levels may occur for several weeks [31]. Several studies report on the lethal toxicity of imidacloprid after repeated ingestion [31,32]. However, sublethal effects, particularly impaired learning and orientation, have been induced at levels as low as 0.1 ng per bee [33]. Foragers may be exposed to as much as 0.6 ng imidacloprid per day when Gaucho-treated sunflowers are the primary nectar and pollen source of a colony [30]. Colin et al. [34] reported impaired foraging performance after exposure to imidacloprid at levels as low as 6 ppb. Similarly, Decourtye et al. [35] detected changes in foraging behavior at 4 ppb imidacloprid in sugar water, and both demonstrated reduced visitation to syrup feeders contaminated with this insecticide at 3 ppb and 24 ppb, respectively. "

"The impact of pesticide exposure at the sublethal level should not be underestimated as these effects may induce physiological impairment that ultimately results in the loss of disoriented foragers and overall decline in colony health."

Full paper:
Bethany S. Teeters, Reed M. Johnson, Marion D. Ellis, And Blair D. Siegfried, (In press) Using video-tracking to assess sublethal effects of pesticides on honey bees (apis mellifera l.), Environmental Toxicology and Chemistry.