Caterpillar genders

[ROBERT BUTCHER]

> Do caterpillars have a gender?
Yes. Either male or Female. 
Most species of lepidoptera are sexual, and thus they exist in two 
forms, male or female. However, examples of parthenogenesis exist in 
which only females exist. Hermaphrodites (both male and female 
functions in the same organism) are not known in lepidoptera (moths 
and butterflies)

 Do female
> caterpillars turn into female butterflies/moths, or are they gender-
> neutral - and perhaps have some clever means of determining if
> ButterflyWorld needs more males or females at that time, and
> become whatever is needed?
Males become males, females likewise only females.
Sex is determined early after egg fertilisation in a manner 
simplistically similar to mammals like us except that females are 
heterogametric (W/Z) and males arent (In mammals it is the male that 
is heterogametric..X/Y and females carry only the Y chromosome). 
Therefore, female caterpillars will develop into female 
moths/butterflies, and males likewise into males.
Their is no known ability to sex change (e.g .females become males as 
in say some fish) in response to a skewed sex ratio in the local 
population). Neither is their any known naturall;y evolved 
environmental sex determination (e.g. temperature during development 
affects sex, such as in many reptilians like crocodiles), but see 
below under exceptions.

However, two sorts of exceptions, albeit relatively rare, are known.
(1) gynadromorph / intersexes. (Fairly common in cultured lepidoptera 
of some species, but less common in the "wild").
Here a "female" butterfly/moth will have some morphology of a "male" 
or visa versa. This is not a hermaphrodite. What happens is that 
after initial sex determination at fertilisation determined by master 
gene(s) on the sex chromosomes in some cells either factor(s) act to 
inhibit the sex determination cascade down stream of the sex genes 
and so these cells develop as the opposite sex (giving a mosaic 
pattern according to the cells that are affected and at what point 
during development). This is analagous to the effect of antibarnacle 
paints on the sex of many marine crustaceans you may have heard 
about, or the PBD? in PVC food wrappings in humans etc). Another is 
that as the fertilised egg commited to female development (WZ) 
divides to form all the cells that will constitute the organism, in 
rare cases one of the sex chromosomes is "lost" (non-dysjunction) and 
so all the cells derived from this, now carrying only the W 
chromosome, will be committed to being male. Again the mosaicism seen 
depends upon when the dysjunction happened in the cellular 
differentitaion / replication phase of development.

(2) Feminisation
Genetically determined males are modified to develop as females. 
Usually the caterpilla and adult will appear as a female and so 
this will go unnoticed. Indeed only molecular genetics will allow 
you to see that the female is indeed genetically determined as a 
male!! However, If this is not complete in all tissues (e.g. the 
bacteria is not in all tissue..see below), mosaic gynandromorphs will 
result. 
It has recently been shown that in the asian corn borer moth 
(sorry, cant remember the latin name at present) that a bacteria from 
the Wolbachia pipientis subgenera, a group of intracellular parasites 
that are widespread in insects, cause genetically determined males to 
develop as females. the site of action is unknown, as is the 
frequency of this across all lepidoptera.
Hope this answers your questions, but ask if not
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