Aphids are recognized as some of the world’s most economically damaging pests. These sap-sucking pests cause stunted growth, diminish grain quality, and reduce crop yields. Not to mention they are known vectors of plant viruses, further compounding risk to crops.
As scientists search for new ways to stay one step ahead of these pesticide resistant pests, recent studies are now investigating the use of tiny bacteria that live inside aphids, known as endosymbionts, for pest management.
Similar strategies have proven effective in addressing disease vectors, such as the transfer of the bacteria Wolbachia into mosquitoes to reduce their ability to transmit viruses topeople. Theoretically, this approach holds promise for agricultural purposes. However, Australia currently lacks comprehensive data regarding aphid endosymbionts, which hinders the establishment of future research endeavours.
A recent study led by Dr. Qiong Yang and undertaken by researchers at the University of Melbourne aims to create new pest control strategies – ones that don’t rely on chemical insecticides, by addressing this knowledge gap around endosymbionts, as part of the Australian Grains Pest Innovation Program (AGPIP) supported by the GRDC.
What are endosymbionts and why do they matter?
Like our own microbiomes, aphids have intricate relationships with a diverse community of microbes in their bodies. Some of them are mutualistic endosymbionts. These microbes aid in nutrition and reproduction and even influence how aphids spread viruses, react to insecticides, cope with heat stress, and defend themselves against predators.
Researchers are investigating the possibilities of manipulating endosymbionts to reduce the damage aphids cause to crops, control their population size and reproduction, limit the spread of plant diseases they carry, and better leverage natural predators to control aphid populations.
Most aphids inherit their endosymbionts, and they differ across populations. Innovative studies are now exploring the possibilities of transferring endosymbionts between aphids through microinjections, like a tiny aphid vaccine. This technique aims to manipulate various traits in aphid pests and could be used to create new avenues for pest control.
The establishment of laboratory populations with specific manipulated endosymbionts, such as those that reduce disease transmission, means modified aphids could be introduced into wild populations to pass on their bacteria and provide a natural way to control pests and protect crops. A possible game-changer for pest control strategies.
However, exploring these potential benefits requires an understanding of which endosymbionts live in which aphids, and where different species are distributed. In Australia we lacked this critical information, until the findings uncovered by Dr. Qiong Yang and the research team.
Understanding Australia’s unique endosymbiont landscape
Between 2019 and 2021, the research team conducted a study to uncover a rich dataset of endosymbionts within various aphid species. Their research spanned from urban Melbourne to agricultural areas across southern Australia, where they collected 123 samples of over 30 different aphid species. Samples were obtained from 64 host plants, across 122 localities.
To identify the endosymbionts within the aphids, the researchers used a technique called metabarcoding, which involves sequencing DNA. Researchers then established controlled populations of various aphid species with known endosymbionts to investigate how long these endosymbionts survive and how they interact with host aphids.
Across the study, an endosymbiont called Buchnera emerged as the predominant primary endosymbiont as expected. However, researchers also identified eight secondary endosymbionts, including Regiella, Rickettsia, Rickettsiella, Serratia and Wolbachia that could be maintained in laboratory aphid populations. This is a significant finding as it offers a valuable donor resource for future research involving the transfer of these endosymbionts to other aphid species.
In nineteen aphid species, including some of the most agriculturally important species such as oat aphid (Rhopalosiphum padi), green peach aphid (Myzus persicae), Russian wheat aphid (Diuraphis noxia) and bluegreen aphid (Acyrthosiphon kondoi), researchers were unable to identify any secondary endosymbionts. This raises the potential to introduce secondary endosymbionts into these recipient species, essentially giving them new traits for the purpose of pest control.
The research found that Australian aphid populations had fewer secondary endosymbionts than aphids from elsewhere in the world. This difference may allude to the natural patterns of infection among aphid populations, influencing endosymbiont distribution and how effectively they are passed from one generation of aphids to the next.
It appears that the persistence of specific endosymbionts might be influenced by the type of host plant on which the aphids are raised. In some cases, aphids needed to stay on their original host plant to keep their endosymbionts and could then be consistently maintained over multiple generations in the laboratory. However, other endosymbionts were lost regardless of the host plant. This suggests that factors beyond the type of host plant, such as temperature, may affect the maintenance of endosymbionts. The inability to maintain certain endosymbionts within laboratory-cultured aphids raises important questions including how long these endosymbionts will survive once released into the wild.
The researchers also found that aphid populations from urban environments had more diverse endosymbionts compared to those from agricultural regions. This discovery raises the question of whether secondary endosymbionts might be more advantageous for urban aphids compared to their agricultural counterparts. This may be attributed to the fewer types of pesticides available for use in urban areas compared to farms.
Due to the intensive use of a limited range of pesticides, aphids in urban areas might benefit from having endosymbionts that provide resistance compared to agricultural regions. This means endosymbionts are more likely to be found in a greater diversity in urban areas. Differences in the temperature across cities, which often traps heat, and the greater variety of inner-city plant species are other factors that could be influencing the spread of endosymbionts within aphid populations.
A promising path for pest control
We expect that pest management research could benefit significantly from identifying potential donor species for the transfer of endosymbionts into pest aphid species. These microscopic bacteria, often overlooked, have the potential to influence everything from pesticide resistance to virus transmission among aphids.
While we are still some distance away from putting this into practice in the field, as our understanding of endosymbionts and how they operate grows through AGPIP, we open doors to innovative strategies for managing pest populations and safeguarding our crops.
To read more about the research undertaken by the Pest & Environmental Adaptation Research Group at the University of Melbourne, you can find the paper here.
This research is being undertaken as part of the Australian Grains Pest Innovation Program (AGPIP). AGPIP is a collaboration between the Pest & Environmental Adaptation Research Group at the University of Melbourne and Cesar Australia. The program is a co-investment by the Grains Research and Development Corporation (GRDC) and the University of Melbourne, together with in-kind contributions from all program partners.