Hi Sibylle

We have not looked at the antifeedant effects of neem limonoids because we deal mostly with haematophagous insects.  However, we have looked for effects of mixed limonoids in other ways and to be honest we have never been able to identify any activity of any kind against the insects we deal with, whether azadirachtin was included or not.  

I do not doubt the antifeedant effect of various of the limonoids on phytophagous species but logically, if the limonoids are repellent, wouldn't that deter phytophagous species from feeding on treated plants?  So I am inclined to suspect that claimed repellent effects of neem limonoids are due to some other factor that those reporting them have not taken into account.

Ian

Hi Ian,

Thank you, - quite interesting your response. The antifeedant properties seem irrfutably in existence, having in mind all these papers on the impact of salannin, nimbin, nimbidin, and the like (such as Yamasaki & Klocke 1989; Govindachari TR et al 1996; Su & Mulla 1998; Koul O. et al 2004 and some others).  But few mention the repellent effects, indeed. However, repellency is a property that you could easily  measure by looking at their reactions simply  (meaning I don't understand what you actually mean, when saying "claimed repellent effects of neem limonoids are due to some other factor that those reporting them have not taken into account"... Do you mean, these are, in fact, antifeedant effects not having properly been described  and monitored as yet?

"....we have looked for effects of mixed limonoids in other ways and to be honest we have never been able to identify any activity of any kind against the insects we deal with....." 

Which one were these?

There has been quite some research in India that might go unbeknownst to those outside the country. May some response from there ….?

Sibylle

I know this good paper in 2008, realised in Niger, West Africa http://www.ncbi.nlm.nih.gov/pubmed/18651964

Hi Sibylle

Sorry I missed the notification of your response to my comments in October and have just picked it up.

When I refer to the "claimed repellent effects of neem limonoids" I was thinking of the claims made by those people using neem and its extracts for deterrence of blood feeding insects such as mosquitoes, fleas, and lice.  As far as I can see these are just claims with no real substantive evidence in support of those claims.

 If neem extracts do repel in the true sense it would have the opposite effect from that which is required for the anti-feedant effect, i.e. phytophagous insects should be repelled from treated plants, which we can reasonably assume not to be the case because those insects do feed off neem treated plants and suffer the anti-feedant effect as a consequence.  

My suggestion is that products containing neem that are sold for repelling mosquitoes etc may derive their activity from some other component of the formulation or perhaps, at the most basic level, the insects are deterred from biting either by the sticky nature of the neem oil component or else the unpleasant allium-like odour of the neem.

With regard to the comment "....we have looked for effects of mixed limonoids in other ways and to be honest we have never been able to identify any activity of any kind against the insects we deal with....." I was referring to the claimed effects of neem to kill blood feeding insects, such as lice, when applied topically to the insects.  There are numerous products on sale around the world that are claiming efficacy from azadirachtin and the other large limonoids against insects that could not possibly ingest the compounds due to their blood feeding habits and these compounds could also not possibly enter the insects via the cuticle.  Hitherto none of these products has a defined mode of action but the makers imply that as neem is considered a "wonder" insecticide the products work in a similar way to how neem controls phytophagous insects.  Largely a matter of BS baffles brains, as most of the purchasers have no idea how the material works against any insect - they just like the idea of a natural "wonder drug".

Ian