Boivin T, Candau J-N. 2007. Flow cytometric analysis of ploidy levels in two seed-infesting Megastigmus species: applications to sex ratio and species determination at the larval stage. Entomologia Experimentalis et Applicata 124: 125-131.
These authors tested the utility of flow cytometry for both species and sex discrimination in the larvae of two congeneric species of pest wasps. These wasps are recently-introduced pests of cedar trees in southern France, and cannot be identified to either species or sex by morphology during their larval stages. In this genus, most species have an obligate larval diapause that can last more than 5 years. Thus, a method for determining sex ratios (for population-dynamics studies) and species (for invasion dynamics) was required.
Their method of flow cytometry involved a commercially-available staining solution containing DAPI, and no mention of known standards appears. They do not report absolute or relative genome sizes, rather they report ratios of cells of various ploidy levels.
Flow cytometry was shown to be effective for identifying both sex and species in this system. Like other hymenoptera, these species have haplodiploid sex determination, though they differ in the details: Megastigmus pinsapinis are thelytokous, M. schimitscheki are arrhenotokous. Species can be discriminated in female larvae, because M. schimitscheki female larvae include large numbers of haploid cells. The failure of species discrimination among male larvae is not critical, as the sex ratio of M. pinsapinus is severly female-biased, with males occuring at the rate of about 1 in 4000.
The discovery of haploid cells in the abdomens of female M. schimitscheki lead to a brief discussion and some speculation regarding haploidization and gametogenesis. However, I am under the impression that universally among animals, female mieosis does not complete until after fertilization, and thus eggs are never actually haploid. A reference in this section, Pannebakker et al. (2004), may shed light on this issue.
Glossary of Terms:
Arrhenotoky: females and males result from fertilized and unfertilized eggs, respectively.
Thelytoky: parthenogenetic diploid females develop from unfertilized eggs, males are absent or rare.
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