Abstract
Trissolcus basalis (Wollaston) (Hymenoptera, Scelionidae) is an egg-parasitoid of the southern green stink bug, Nezara viridula (Linneaus) (Hemiptera, Pentatomidae). Many behaviors associated with female T. basalis host-finding and acceptance are mediated by chemosensory pathways, for which olfactory, gustatory and ionotropic receptors have been previously identified. Odorant binding proteins (OBPs) are small, globular proteins, one of the functions of which is the transport of odorant ligands through the aqueous lymph of chemosensory sensilla to these receptors. We identified 18 classical OBP sequences in the T. basalis genome and transcriptomes sharing an average 26.8% pairwise identity. Gene tree analyses suggest very limited lineage-specific expansion and identify potential orthologs among other scelionids and Hymenoptera. Transcriptome mapping and qPCR comparison of expression levels in antennae and bodies of both sexes determine that at least five TbOBPs are preferentially expressed in the female antennae. These are, therefore, prime candidates for further study to determine their role in detecting host-produced semiochemicals.
Highlights
The subfamily Telenominae (Hymenoptera, Scelionidae) encompasses nearly a thousand species of egg-parasitoids, many of which have proven to be valuable as biological control agents of their host insects (Laumann et al 2008; Talamas et al 2015; Sacaccini et al 2020)
In gregarious species, telenomines mate on the host eggs from which the wasps emerge, suggesting that evolution of the chemosensory ability of the female wasp to find eggs may be a driver of the speciation mechanisms that have resulted in their high species richness (Loch and Walter 2002)
The molecular weights range from 14.5–22.7 kD. Both atypical Odorant binding proteins (OBPs) and C-plus OBPs (Xu et al 2003; Spinelli et al 2012) were used as queries, none of the sequences found in the T. basalis genome or transcriptomes display those motifs
Summary
The subfamily Telenominae (Hymenoptera, Scelionidae) encompasses nearly a thousand species of egg-parasitoids, many of which have proven to be valuable as biological control agents of their host insects (Laumann et al 2008; Talamas et al 2015; Sacaccini et al 2020). Numerous studies have demonstrated that these minute wasps (generally 0.5–2.5 mm in total length) locate eggs to attack by orienting to semiochemicals produced by their adult hosts. These include sex pheromones, alarm pheromones, aggregation pheromones, and cuticular hydrocarbons (Isidoro et al 2001; Yang et al 2016). Behavioral experiments have demonstrated that females of T. basalis respond to the plant volatiles 3-methylbutanoic acid and p-benzoquinone (Slimani et al 2016); to the N. viridula kairomones (E)-2-decenal, 4-oxo-(E)-hexenal, and the sesquiterpenes trans- and cis-(Z)-alpha-bisabolene epoxide; the stink bug cuticular hydrocarbon n-nonadecane; and to mucopolysaccharides on the surface of an egg mass (Bin et al 1993; Mattiacci et al 1993; Colazza et al 2007; Laumann et al 2009)
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