Improved control of Rhopalosiphum maidis and Acyrthosiphon pisum, using the predatory natural enemy Harmonia axyridis carrying entomopathogenic fungi.

Background: Aphids are important agricultural and forestry pests that not only directly harm plants, but also transmit various plant viruses. Biological control, including the use of entomopathogenic fungi (EPFs) and predatory natural enemies, can effectively control aphids. However, there are few reports on the combined use of natural enemies carrying EPF to enhance the efficiency of aphid control.

Results: In the present study, we evaluated the compatibility of five EPF strains with adults of the Harlequin ladybird (Harmonia axyridis). The pathogenicity, impact on predatory function, and fertility of EPF on H. axyridis were assessed as indicators, and the control efficiency of the predator carrying EPF was evaluated. The results showed that four EPF strains did not exhibit direct or indirect pathogenicity toward H. axyridis. Additionally, they did not significantly affect the survival rate, predation function, egg production or hatching rate of adult H. axyridis. The feeding rate of H. axyridis on Acyrthosiphon pisum was significantly lower than that of the control group after 0 h of starvation, but there were no significant differences observed following 24 and 48 h of starvation. Under semi-field conditions, the release of H. axyridis that had been treated previously with Metarhizium rileyi resulted in a significantly higher control of A. pisum and Rhopalosiphum maidis on Day 4 with aphid mortality rates of 83.33% and 98.35%, respectively. In comparison, the H. axyridis treatment group exhibited 46.22% and 84.16% mortality, respectively, whereas the M. rileyi treatment group experienced 10.67% and 61.06%, respectively.

Conclusion: Four EPF isolates showed no effect on the survival and predation of adult H. axyridis. The M. rileyi treatment had no effect on the reproduction of H. axyridis, yet H. axyridis adults carrying EPF conidia had a significantly higher control efficiency toward two species of aphids compared to each type of enemy alone. Therefore, predator dissemination of EPF may be an efficient and low-cost strategy for controlling of aphids. © 2025 Society of Chemical Industry.