Monarch eggs / predation / sibling rivalry

[Paul Cherubini]

Martha Rosett Lutz wrote:

> I don't know how significant a factor this is (especially in the field
> versus the lab), but I have direct evidence that newly-hatched Monarch
> larvae are predators of Monarch eggs.  Also, older larvae will eat younger
> ones.  

Yes this is fairly common in crowded rearing conditions and perhaps
also in the spring in high population years when a half dozen or more
monarch eggs and/or larvae can sometimes be found on oa single 
small milkweed shoot.

But this past summer the monarch egg predation was so bad in the upper midwest
that one could  find literally hundreds of eggs without too much effort but have a  
difficult time finding a single living caterpillar. 

Anyway, one point to keep in mind is that low numbers of monarchs do not
mean the environment is polluted  or degraded.  It may just mean the egg 
predators are having a banner year. So I think scientists should start thinking
about what biotic and abiotic factors might be influencing  the abundance of 
monarchs egg and young larval predators on a wide regional scale in order to
better understand the causes of the huge annual fluctuations in monarch
populations.  

Paul Cherubini

 
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