Abstract
The proboscis extension reflex (PER) applied to restrained individuals is an important method to assess the sucrose responsiveness under laboratory conditions. Several authors have used the PER bioassay to assess behavioral effects of pesticides. A lot of them reported the difficult to use this method with non-Apis bees showing that this basic technique cannot be applied for all bees. The aim of this study was to evaluate the sucrose responsiveness of two brazilian stingless bees, Melipona scutellaris and Scaptotrigona postica using two different protocols: the traditional one and the new one where bees have free movements. In both cases, the bees were anesthetized (freezing) and inserted into plastic tubes with the tip cut out. After a starvation period were offered an increasing concentration of sucrose-water solution (w/v). Between the solutions, were offered water. With the traditional method, the sucrose responsiveness were observed only in M. scutellaris bees (12.5% of tested bees) in just one sucrose concentration (75%). Using the methodology with free movements, both species showed sucrose responsiveness in all concentrations (25%, 50% and 75%) tested. The number of M. scutellaris bees that had sucrose response ranged from 53.7% to 76.2 % depending on the sucrose concentration. And the number of S. postica ranged from 54% to 79%. These results showed that using the methodology with free movements the sucrose responsiveness can be assessment non-Apis bees.
Highlights
The Proboscis Extension Reflex (PER) considers that the bees extend their proboscis reflexively when the chemoreceptors in their antennae, buccal apparatus or tarsi are stimulated with sucrose solution (Takeda, 1961; Bitterman et al, 1983; Menzel, 1999).This assay is considered a quantifiable and reliable method since it reproduces the bee-plant interaction: when the bee lands on the flower its gustative receptors are stimulated by the nectar and in response, the bee extends its proboscis, collecting the nectar and memorizing the floral odours that, once memorized, are fundamental for the recognition of flowers in the foraging
The mortality rate of the M. scutellaris bees was of 20%, both for the traditional PER and for the PER in tube like eppendorf
For the S. postica bees, the mortality rate in the PER test in the plastic tube was of 6%
Summary
The Proboscis Extension Reflex (PER) considers that the bees extend their proboscis reflexively (unconditioned response) when the chemoreceptors in their antennae, buccal apparatus or tarsi are stimulated with sucrose solution (unconditioned stimulus) (Takeda, 1961; Bitterman et al, 1983; Menzel, 1999). This assay is considered a quantifiable and reliable method since it reproduces the bee-plant interaction: when the bee lands on the flower its gustative receptors are stimulated by the nectar and in response, the bee extends its proboscis, collecting the nectar and memorizing the floral odours that, once memorized, are fundamental for the recognition of flowers in the foraging. Strong similarities were observed between the results with the contained and in free flight individuals (Mauelshagen and Greggers 1993; Pham-Dèlegue et al, 1993)
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