Abstract
BackgroundTrichogrammatids are minute parasitoid wasps that develop within other insect eggs. They are less than half a millimeter long, smaller than some protozoans. The Trichogrammatidae are one of the earliest branching families of Chalcidoidea: a diverse superfamily of approximately half a million species of parasitoid wasps, proposed to have evolved from a miniaturized ancestor. Trichogramma are frequently used in agriculture, released as biological control agents against major moth and butterfly pests. Additionally, Trichogramma are well known for their symbiotic bacteria that induce asexual reproduction in infected females. Knowledge of the genome sequence of Trichogramma is a major step towards further understanding its biology and potential applications in pest control.ResultsWe report the 195-Mb genome sequence of Trichogramma pretiosum and uncover signatures of miniaturization and adaptation in Trichogramma and related parasitoids. Comparative analyses reveal relatively rapid evolution of proteins involved in ribosome biogenesis and function, transcriptional regulation, and ploidy regulation. Chalcids also show loss or especially rapid evolution of 285 gene clusters conserved in other Hymenoptera, including many that are involved in signal transduction and embryonic development. Comparisons between sexual and asexual lineages of Trichogramma pretiosum reveal that there is no strong evidence for genome degradation (e.g., gene loss) in the asexual lineage, although it does contain a lower repeat content than the sexual lineage. Trichogramma shows particularly rapid genome evolution compared to other hymenopterans. We speculate these changes reflect adaptations to miniaturization, and to life as a specialized egg parasitoid.ConclusionsThe genomes of Trichogramma and related parasitoids are a valuable resource for future studies of these diverse and economically important insects, including explorations of parasitoid biology, symbiosis, asexuality, biological control, and the evolution of miniaturization. Understanding the molecular determinants of parasitism can also inform mass rearing of Trichogramma and other parasitoids for biological control.
Highlights
Trichogrammatids are minute parasitoid wasps that develop within other insect eggs
We present the genome sequence of one such asexual, Wolbachia-infected line of Trichogramma pretiosum and a sexual strain of the same species
A total of 12,928 genes were annotated for Trichogramma pretiosum, a value which is more similar to the fig wasp’s (Ceratosolen solmsi) repertoire of 11,412 genes than to Nasonia vitripennis’s 24,388 predicted genes [39]
Summary
Trichogrammatids are minute parasitoid wasps that develop within other insect eggs They are less than half a millimeter long, smaller than some protozoans. Trichogramma (Hymenoptera: Trichogrammatidae) wasps are minute polyphagous egg parasitoids used globally for controlling a variety of agricultural insect pests [1]. They are some of the smallest known insects (smaller than the largest protozoans), with adults measuring only tenths of millimeters in length. The family Trichogrammatidae is one of the earliest branching families of the superfamily Chalcidoidea [2, 3] ( referred to as chalcids) This puts Trichogramma in a position to help us more broadly study the evolution of chalcid parasitoids, a diverse and ecologically important insect group. Trichogramma is an excellent group to use for investigations of the evolution, ecology, and mechanisms of asexual reproduction
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