Record Low Monarch population expected in Mexico this winter.

[Chip Taylor]

The data I've seen for monarchs indicates that egg mortality is high 
- usually in excess of 60%. Mortality of first instars is also high 
so that the number alive after the first 6-7 days ( 4 days per egg 
stage and 2-3 days per first instar) is often less than 15%. Losses 
through the remaining instars result in a total mortality of 97-99+% 
depending on the local conditions, but most often are close to 99%. 
For a female laying 400 eggs this means that on AVERAGE she gives 
rise to 4 individuals - sometimes less or more depending on the 
conditions. The replacement rate from spg to fall varies from 2-3 to 
over 40 females per female. It was extremely low in 2000 quite high 
in 2001 and apparently low again this yr. The replacement rate from 
spg to fall is lower in yrs with spg droughts in TX and summer 
droughts in the midwest. Droughts in the northeast seem to be less 
important. Moderate droughts in MN and WISC in July and August may 
actually be beneficial.

Eggs are eaten by the usual suspects - ants, thrips, lacewing larvae, 
etc. but monarchs do not appear to have egg parasites - perhaps 
because of PAs in the eggs. This is something that needs to be looked 
at.

Chip


>Paul makes a good point about the possible importance of egg 
>mortality in deciding
>Monarch abundance. Does anyone know of any data on survivorship 
>rates in monarch eggs?
>
>
>Patrick
>patfoley at csus.edu
>
-- 

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