Hornets are the largest of the social wasps, and are important regulators of insect populations in their native ranges. These insects are also very successful as invasive species, with often devastating economic, ecological and societal effects. Understanding why they are such successful invaders is critical to managing future introductions and minimizing impact on native biodiversity. Critical to the management toolkit is a comprehensive genomic resource for these insects. In new research, scientists sequenced the genomes of two hornet species: the European hornet (Vespa crabro) and the Asian hornet (Vespa velutina). They also compared these genomes with those of other social Hymenoptera, including the northern giant hornet (Vespa mandarinia). The three hornet genomes show evidence of selection pressure on genes associated with reproduction, which might facilitate the transition into invasive ranges.
Biology of Vespa crabro, Vespa velutina and Vespa mandarinia hornets. Image credit: Favreau et al., doi: 10.1038/s41598-023-31932-x.
There are around 1,200 species of social wasps, including relatively well-known Vespidae yellowjackets and hornets, and lesser-known species of Stenogastrinae and Polistinae.
They display a huge variety of ecological and life-history characteristics; e.g. the colony size varies enormously, from species with less than 10 individuals in the society (e.g. as found in the Stenogastrine hover wasps) to those with tens of thousands of workers (e.g. Vespula species).
Some species have many reproductive queens (e.g. epiponine wasps, like Metapolybia) whilst others are monogynous (e.g. Vespa crabro); reproductive hierarchies can be regulated by conventions such as age or size, aggression or pheromones.
The first aculeate wasp genome was published in 2015 (Polistes canadensis), closely followed by the European paper wasp (Polistes dominula).
Currently there are genome sequences published for seven polistine wasp species and nine vespine wasps.
However, evolutionary analyses of these vespine genomes are lacking, and particularly so for the hornets, the Vespa genus.
“To better understand how these species have so successfully expanded their ranges, we investigated the genomes of three types of hornets,” said University College London researcher Emeline Favreau and colleagues.
In their research, the authors sequenced the genomes of the native European hornet — an important top predator, which is protected in parts of Europe — and the invasive yellow-legged Asian hornet, which has become established through much of Europe over the last 20 years threatening native ecosystems.
They compared these with the genome of the giant northern hornet, a species known for its role as pest controller, pollinator and food provider in its native Asian range, but is a recent arrival in North America, where it may threaten native fauna.
By analyzing differences between the three related species, the researchers were able to identify genes that have been rapidly evolving since the species differentiated themselves from other wasps and from one another, and found some noteworthy genes that are rapidly evolving, particularly relating to communication and olfaction.
“We were excited to find evidence of rapid genome evolution in these hornet genomes, compared to other social insects,” Dr. Favreau said.
“Lots of genes have been duplicated or mutated; these included genes that are likely to be involved in communication and in sensing the environment.”
“These findings are exciting, as they may help explain why hornets have been so successful in establishing new populations in non-native regions,” said Dr. Alessandro Cini, a researcher at the University of Pisa.
“Hornets are carried to different parts of the world accidentally by humans. All that is needed is a small number of mated queens to be transported, hidden in cargo perhaps.”
“The genomes suggest that hornets have lots of genes involved in detecting and responding to chemical cues — these may make them especially good at adapting to hunt different types of prey in non-native regions.”
“These hornet genomes are just the beginning,” said University College London’s Professor Seirian Sumner.
“The genomes of more than 3,000 insect species have now been sequenced by efforts around the world, but wasps are under-represented among these.”
“Genomes tell us about aspects of the ecology and evolution that other methods cannot.”
“Evolution has equipped these insects with an incredible genetic toolbox with which to exploit their environment and hunt their prey.”
The findings appear in the journal Scientific Reports.
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E. Favreau et al. 2023. Putting hornets on the genomic map. Sci Rep 13, 6232; doi: 10.1038/s41598-023-31932-x
