Record Low Monarch population expected in Mexico this winter.

[Paul Cherubini]

Patrick Foley wrote:

> Is your group keeping enough time series data on 
> Monarchs and natural enemies to see if predator-prey 
> oscillations are going on over time? Or do you have any
> relevant information? If monarchs are the main hosts of 
> some Tachinids or some other insect, then some coupling 
> may be ccurring. If weather fluctuations are
> driving most of the Monarch population fluctuations, then 
> such a coupling may be one way. Monarch pops may drive 
> tachinid posp but not vice versa. I am assuming
> that the ultimate Monarch density regulation comes from either 
> Winter roosting habitat or from Milkweed abundance. DOes 
> anybody have a handle on that?

Pat, in private industry an employee must produce product 
and/or results or be fired. Same deal in the academic community.

Because of this situation, scientists will tend to focus their attention 
on butterfly mortality factors that can be easily observed and quantified 
and therefore will quickly produce publishable results.

So the scientists mainly study mortality factors like weather extremes,
tachinid fly parasitism, milkweed condition and abundance, overwintering
mortality, etc.  But they will largely ignore mortality factors like egg
predation which may be far more significant because it is logistically
difficult to physically observe and measure this predation (egg predation
by ants, for example, can occur at night) .

In Minnesota and northern Iowa this past July and early August I observed
a great abundance of monarch eggs on milkweed plants but no caterpillars.
Therefore my reasonable conclusion was that a tremendous amount
of egg predation was occurring that would prevent the normal buildup of migrant
monarch butterflies in late summer.

As early as Aug. 21 I predicted a record low population of monarchs in 
Mexico this coming winter based on this severe egg predation and lack 
of caterpillar abundance (beyond the first instar).  

I would be a hypocrit if I didn't also mention there are other possible reasons
for the lack of caterpillar abundance beyond the first instar besides egg predation. 
For example, there might be some kind of obscure disease that affects 
periodically affects monarch eggs or first instar caterpillars that has never been 
studied.   

Paul Cherubini

 
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