sex ratio

[Robert Butcher]

Hi everyone,
 for those who people who are in a position to comment upon sex 
ratios in lepidoptera....Have you ever noticed a strong female biased 
species? 

Just curious as a male killing bacteria (not the ricketsia 
species associated with ladybirds, but rather another isolate of 
Wolbachia) has been reported in an african lepidoptera (Hurst et al. 
1999 proc roy. Soc. lond. B). Usually these bacteria, which are 
maternally transmitted only (they cannot pass on through the 
sperm, only the ova), kill sons in species where they are gregarious, 
so either the daughters eat the dead brothers eggs (and hence each 
daughter sort of gets a double nutrient alloquote from the mother), 
or the death of the males results in more food for the daughters by 
reducing sibling rivarly. Its hence easy  to see how this evolved in 
gregarious and food limited species like ladybirds, and indeed many 
lepidoptera. 
And hence my question.

What is also interesting, however, is this reported 
lepidoptera species with male killing Wolbachia lays single eggs per 
host plant, so neither of the above two benefits are immediately 
obvious! of course it may well be that it is not solitary on 
other host plants and so sibling rivalry ocurrs on a different host 
plant. It is certainly not likely to be a recent infection into a 
host that isnt gregarious and will be selected against, since in this 
species females form lecks and compete against each other  for males. 
therefore the infection, and female biased secondary sex ratios as a 
consequence, have been around long enough for mating behaviour to be  
altered!!

Hope that was of interest to some of you. If anyone wants to know 
more i can pass on a copy of the manuscript, just ask.
Cheers
Rob
Robert Butcher,
Evolutionary and Ecological Entomology Unit,
Department of Biological Sciences,
Dundee University,
Dundee, DD1 4HN,
Tayside, Scotland,
UK.
Work Phone:- 01382-344291 (Office), 01382-344756 (Lab).
Fax:- 01382-344864
e-mail:- r.d.j.butcher at dundee.ac.uk