Why are larvae of the social parasite wasp Polistes sulcifer not removed from the host nest?
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A challenge for parasites is how to evade the sophisticated detection and rejection abilities of potential hosts. Many studies have shown how insect social parasites overcome host recognition systems and successfully enter host colonies. However, once a social parasite has successfully usurped an alien nest, its brood still face the challenge of avoiding host recognition. How immature stages of parasites fool the hosts has been little studied in social insects, though this has been deeply investigated in birds. We look at how larvae of the paper wasp obligate social parasite Polistes sulcifer fool their hosts. We focus on cuticular hydrocarbons (CHCs), which are keys for adult recognition, and use behavioral recognition assays. Parasite larvae might camouflage themselves either by underproducing CHCs (odorless hypothesis) or by acquiring a chemical profile that matches that of their hosts. GC/MS analyses show that parasite larvae do not have lower levels of CHCs and that their CHCs profile is similar to the host larval profile but shows a reduced colony specificity. Behavioral tests show that the hosts discriminate against alien conspecific larvae from different colonies but are more tolerant towards parasite larvae. Our results demonstrate that parasite larvae have evolved a host larval profile, which overcomes the host colony recognition system probably because of the lower proportion of branched compounds compared to host larvae. In some ways, this is a similar hypothesis to the odorless hypothesis, but it assumes that the parasite larvae are covered by a chemical blend that is not meaningful to the host.
KeywordsPolistes wasps Obligate social parasites Nest–mate recognition Parasite integration Larval recognition
We thank Wendy Castle for help genotyping larvae and Marcus Kronforst for his support with the genetic data analysis, particularly with the STRUCTURE program. We thank Mr. Daniele Melotti for permission to collect wasps from his property. We are grateful to the anonymous referees for their very helpful comments. The experiments reported comply with the current laws of the countries in which they were performed. This research was based on work supported by University of Florence and by the US National Science Foundation under Grant IBN-9975351. Financial support was provided by the Ente Cassa di Risparmio through a fellowship to FRD (within the grant 2003/0964) and a fellowship “Ficai” to CC.
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