Asexuality cured: The relations and differences between sexual and asexual Apoanagyrus diversicornis

We investigated whether asexual (thelytokous) Apoanagyrus diversicornis and sexual (arrhenotokous) A. diversicornis (Hymenoptera: Encyrtidae) belong to the same biological species. The strains are allopatric and there are no morphological differences. The sexual A. diversicornis strain originates from south-western Brazil, It was introduced into Africa for the biological control of the cassava mealybug Phenacoccus manihoti. The asexual strain parasitizes P. herreni in Colombia. Feeding antibiotics to asexual A. diversicornis or rearing parasitized hosts at 33 instead of 25 degrees C led to male offspring production. These males could be crossed with virgin females of the sexual strain, leading to fertile female (i.e. hybrid) offspring. There were no indications of hybrid breakdown. Thus, asexuality in A. diversicornis is caused by microorganisms, can be cured, and the two strains belong to the same biological species. The microorganisms associated with thelytoky in A. diversicornis belong to the genus Wolbachia. There were differences between A. diversicornis strains and between host species in survival probability from egg to adult. In addition, some mortality was associated with the feeding of tetracycline and with the production of males, but not with rifampicin, sulphadiazine (which was not effective), or a temperature increase from 35 to 33 degrees C. Survival of hybrids was intermediate between the survival probabilities of the parental strains. Male behaviour and function were not different between the strains, but female behaviour clearly was. Females of the thelytokous strain were less often inseminated by males of either strain than were arrhenotokous females. This suggests a difference in the rate of decay between expressed traits (female sexual behaviour, which is possibly selected against) and traits that are not expressed (male sexual behaviour and function).