Hi all
In some folks version of reality, everything is either good for you or bad for you, whereas in reality everything is a mix. For example, nectar frequently contains various alkaloids, some of which are toxic, along with the various sugars. What these are doing there is the subject of much speculation, as you will see below. One suggestion is that the plant simply has limited control over the alkaloids, which are expressed in the leaves to deter herbivores but may be less appropriate in the nectar. 

> Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as antiherbivore
defences are frequently present in floral nectars.

The occurrence of secondary metabolites in nectar has been
reported in at least 21 angiosperm families (Adler 2000).
Little is known about the significance of these nectar components
in plant–pollinator relationships, or about the possible
tradeoffs between defence and attraction. Various
hypotheses have been proposed to explain the apparent paradox
of deterrent compounds in a pollinator attractant. 
For example, secondary metabolites in nectar could
attract effective pollinators while deterring nectar robbers
or inefficient pollinators. 

Alternatively, these compounds could
help to protect nectar from degradation due to microorganisms
such as yeasts (Herrera et al. 2008); and there is some
evidence that secondary metabolites in nectar could have
indirect benefits by reducing the pathogen loads of pollinators. 
Not to be excluded is the possibility
that secondary metabolites are present in nectar as
a pleiotropic consequence of plant defence chemistry.

We have demonstrated that the nicotine tolerance
of three bird pollinators depends on both the nicotine and
sugar concentrations of artificial nectar. 

Increasing sugar concentration is likely to mask the bitter
taste of alkaloids, and a sweeter solution is also a more profitable
diet that pollinators might choose to consume despite
the presence of secondary metabolites.

The pyridine alkaloid nicotine, highly toxic and deterrent to herbivores, 
is one of the best-studied secondary metabolites in terms of plant defence. 

In the case of nicotine, the dose-dependent deterrent effect on 
honeybees is stronger in dilute artificial nectars (Köhler et al. 2012).

	
Lerch‐Henning, S., & Nicolson, S. W. (2013). 
Bird pollinators differ in their tolerance of a nectar alkaloid. 
Journal of Avian Biology.

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