Abstract
The simple nervous system of the honey bee compared with vertebrate species makes it a good animal for studying effects on behaviour and neurology. Development is not complete at adult emergence and bees continue to mature during the first eight to ten days of adult life. The cuticle and body hairs stiffen and gland development and fat body growth is completed within the first five days (Winston, 1987).
Amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS-PDC) is a progressive neurological disease found predominantly on the island of Guam, and it presents with features of Alzheimer’s disease, Parkinson’s disease and ALS (Stone, 1993). Flour made from cycad seeds has been implicated in the onset of ALS-PDC, and has been found to impair motor, olfactory and cognitive abilities in mice (Wilson et al., 2002; Shaw & Wilson, 2003). A sterol glucoside, β-Sitosterol-β-D-Glucoside (BSSG), was identified as the most likely molecule within the cycad flour to be causing the impairments (Wilson et al., 2002) and is toxic to cells in the rat cerebral cortex (Khabazian et al., 2002).
BSSG was administered to honey bees in food at concentrations of 20 nM, 2 μM and 200 μM. A control group was fed untreated food as a comparison. Bees treated with the herbicide paraquat were also examined because, like BSSG, it targets dopamine pathways of the brain. Paraquat is an herbicide that is toxic to many species and leads to a dose-dependent reduction in dopaminergic neurons and a decrease in locomotor activity in mice (Brooks et al., 1999). Effects of BSSG and paraquat on honey bee locomotor activity were examined using the following assays: motor activity, ability to right after being flipped, and performance in a climbing test. Motor abilities were tested in adult worker bees at ages of one, four and six days after emergence. To examine potential effects of BSSG and paraquat on sensory processing, sucrose sensitivity was measured in seven-day old bees by presenting them with solutions of 0.1%, 3%, 10%, 30% and 55% sucrose. Learning ability was tested in eight-day old bees using single trial olfactory conditioning with eugenol scent as the conditioned stimulus; either 10% or 55% sucrose solution was used as the unconditioned stimulus.
BSSG did not affect motor behaviour but paraquat effects were seen in one-day old bees in righting, and in four- and six-day old bees in flying behaviour. BSSG and paraquat both impaired honey bees’ responses to sucrose, but neither were found to affect single trial olfactory conditioning. At one week of age worker honey bees also do not respond well to low and moderate sucrose solutions. The results also show that behavioural development continues after honey bees emerge as adults. One-day old bees are unable to fly and some motor behaviours are still developing until bees are four to six days old.