There are few bigger enemies for an aphid than ladybirds — but the threat from the predatory beetles could be about to get even greater.
Chinese researchers have found that the harlequin ladybird (Harmonia axyridis) can carry fungi which infect and kill the pea aphid (Acyrthosiphon pisum) and green corn aphid (Rhopalosiphum maidis) without any negative effect on its own ability to feed on the crop-damaging pests.
Harlequin passes tests
They tested five strains of fungi that are known to infect certain insects, finding that four of them didn’t affect the health of the ladybirds, or their ability to feed and reproduce. Only Beauveria bassiana proved to have a negative effect on the specimens used in the study, meaning it was rejected as a possible option for use in further tests, which explored the use of the ladybirds as a natural pesticide delivery agent.
For pot experiments, they applied fungal spores to the beetles by briefly rolling them in a fungal culture until they were covered. After a four-day period of starvation, they were introduced to their prey, and ladybirds carrying Metarhizium rileyi were the best performers against both the aphid species. They killed 83.33% and 98.35% of A. pisum and R. maidis, respectively, with the ladybirds alone killing 46.22% and 84.16% and the fungus alone seeing off 10.67% and 61.06%.
“Ladybirds actively search for aphids and during the feeding process, the entomopathogenic conidia loaded on the surface of ladybirds can be transmitted to aphid populations,” the researchers from Jilin Academy of Agricultural Sciences wrote in the journal Pest Management Science.
“However, further clarification is needed on the transmission of EPF to pest populations in the field. The use of ladybirds carrying EPF conidia might not only reduce the costs of pathogen application and formulation but also improve the control of aphid pests.”
Future fungal backpackers
While some studies have shown that certain fungal pesticides can affect natural enemies, the harlequin ladybird is not the first invertebrate to be used effectively as a carrier, with no detrimental effects. The scientists pointed to studies using other ladybirds and fungal species as a dual attack against specific pests, as well as fungus-carrying tiny wasps and nematodes, suggesting that the approach has promise as part of Integrated Pest Management strategies.
Harlequin ladybirds are mainly known as being one of the most prolific invasive species, which are now widespread in Europe and the Americas, sometimes at the expense of native species. Perhaps its potential new role as a tooled-up super pest controller could bring about an image change.
