In the Hymenoptera, males develop as haploids from unfertilized eggs and females develop as diploids from fertilized eggs. In species with complementary sex determination (CSD), however, diploid males develop from zygotes that are homozygous at a highly polymorphic sex locus or loci. We investigated mating behavior and reproduction of diploid males of the parasitoid wasp Cotesia vestalis (C. plutellae), for which we recently demonstrated CSD. We show that the behavior of diploid males of C. vestalis is similar to that of haploid males, when measured as the proportion of males that display wing fanning, and the proportion of males that mount a female. Approximately 29% of diploid males sired daughters, showing their ability to produce viable sperm that can fertilize eggs. Females mated to diploid males produced all-male offspring more frequently (71%) than females mated to haploid males (27%). Daughter-producing females that had mated to diploid males produced more male-biased sex ratios than females mated to haploid males. All daughters of diploid males were triploid and sterile. Three triploid sons were also found among the offspring of diploid males. It has been suggested that this scenario, that is, diploid males mating with females and constraining them to the production of haploid sons, has a large negative impact on population growth rate and secondary sex ratio. Selection for adaptations to reduce diploid male production in natural populations is therefore likely to be strong. We discuss different scenarios that may reduce the sex determination load in C. vestalis.
Bibliographical noteFunding Information:
We thank Dominique Bordat for supplying C. vestalis from Benin, Lynn Knutson and Beth Sandager for rearing assistance, Greg Veltri of the Flow Cytometry Core Lab at the University of Minnesota Cancer Center for his help in setting up the flow cytometry analyses and Zhishan Wu for letting us use facilities at the University of Minnesota/Minnesota Department of Agriculture Quarantine Facility. This study was supported by the US National Science Foundation and the University of Minnesota Agricultural Experiment Station.
- Biological control
- Constrained sex allocation
- Cotesia plutellae
- Courtship behavior
- Diamondback moth
- Plutella xylostella