Scientists have shed new light on the evolution of an important species of wasp – and believe that the findings could help improve the effectiveness of natural pest control.
Dr Rebecca Boulton, from the University of Stirling, has shown, for the first time, that Lysiphlebus fabarum – a tiny species of wasp – can reproduce with or without a mate. This discovery challenges the previous assumption that asexual females could not mate and produce offspring sexually.
Significantly, the wasps lay their eggs inside small sap-sucking insects called aphids before consuming their host from the inside out — meaning that they are natural pest controllers.
Lysiphlebus fabarum is known to have both sexual and asexual populations but, until now, it was not known whether asexual females could reproduce sexually with males. The discovery opens up new possibilities for improving biological pest control.
Many species of parasitoid wasps are mass-reared and released as a natural alternative to pesticides because they lay their eggs on or in other species, many of which are pests, before the developing wasp larvae consumes their host, killing it in the process.
Asexual reproduction makes it easy to produce large numbers of wasps, but these need to be suitably adapted to local pests and environments to be effective. Currently, Lysiphlebus fabarum is not used commercially despite being found worldwide and naturally targeting aphids.
Developing an understanding of how the species reproduce could help boost genetic diversity in commercially reared lines, making future biocontrol agents more resilient and better adapted.
Dr Boulton, a lecturer in Biological and Environmental Sciences at the University’s Faculty of Natural Sciences, led the study. She said: “In an evolutionary sense, facultative sex seems like a perfect strategy – asexual reproduction is highly efficient, and takes away the costs of finding a mate as well as the risks of failing to find one.
“But sex is really important for evolution. When females reproduce asexually they don’t mix their genes up with any others which limits the potential for evolution to happen.
“If the environment changes, asexual species may be unable to adapt in the same way that sexuals can.
“Facultative sex brings the efficiency of asexual reproduction with the evolutionary benefits of sex and so has been touted as the best of both worlds.
“The results of my study show that there might be hidden costs to facultative sex though as it reduces female wasps’ reproductive success, and this might limit how frequently it occurs in nature.
“The wasps that I studied are an important natural enemy of aphids, they aren’t currently commercially reared, but they are found globally.
“My findings could be used to develop new biocontrol agents that can be used to control aphids throughout the world, harnessing their natural reproductive behaviour to ensure that they are adapted to the hosts and environments that are specific to different regions.”
Dr Boulton reared the wasps in a Controlled Environment Facility (CEF) at the University and had initially planned to put asexual and sexual wasps together, in direct competition, to see which parasitised the most aphids.
However, in the early stages of these experiments she realised the female asexual wasps were behaving unexpectedly and were mating with males from the sexual population.
This led to a change in strategy, as she started to record this behaviour in more detail, before carrying out wasp paternity testing to see whether the asexual females were just mating or actually fertilising eggs.
Once it confirmed that the asexual wasps were engaging in facultative sex, Dr Boulton carried out an experiment where asexual females either mated or didn’t, before examining how successful these females, and their daughters, were at parasitising aphids.
The study involved putting around 300 wasps, each around 1mm long, in their own petri dish with a colony of sap-sucking aphids and counting how many were parasitised.
Lysiphlebus fabarum wasps only live a few days but spend two weeks developing as larvae on their hosts.
The entire experiment, which was carried out across two generations of wasps, took six weeks to run.
On completion Dr Boulton extracted DNA from the wasps and sent it to be paternity tested. When the results were returned it was clear that the asexual wasps which mated were, in most cases, reproducing sexually as their offspring had bits of DNA that were only found in the fathers.
The study, Is facultative sex the best of both worlds in the parasitoid wasp Lysiphlebus fabarum? is published in the Royal Society of Open Science.
It was funded through a BBSRC Discovery fellowship.
Professor Anne Ferguson-Smith, Executive Chair of BBSRC, said: “This is an exciting example of how BBSRC’s Discovery Fellowships are helping talented early career researchers explore fundamental questions in bioscience with real-world relevance.
“Dr Boulton’s work, which measures the costs of sex in this predominantly asexual parasitoid wasp, opens up promising avenues for more sustainable pest control. Supporting curiosity-driven research like this not only strengthens the UK’s research base, but helps drive innovation that benefits the environment, food systems and society at large.”
University of Stirling
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