A Special Pellet and Fungus Offer Multiple Protections to Mealybugs

Jim Crocker
17th May, 2024

A Special Pellet and Fungus Offer Multiple Protections to Mealybugs

The symbiotic fungus Penicillium citrinum, introduced by mealybugs, colonizes and proliferates within their honeydew (a–h), which then serves as a medium for horizontal transmission to other mealybugs (i) and a competitive environment where it suppresses the pathogen Akanthomyces lecanii (j).

Image adapted from: Li et al. / CC BY (Source)

Key Findings

  • Mealybugs feeding on tomato plants develop unique pellet-like structures on their legs that house the fungus Penicillium citrinum
  • These at-leg pellets form through a collaboration of plant secretions and waxy filaments from the mealybugs
  • The fungus within these pellets protects mealybugs by inhibiting harmful fungal pathogens, enhancing their survival
Insects and fungi often form intricate mutualistic relationships, where each partner benefits from the other’s presence. These mutualisms can evolve to become highly specialized, with both insects and fungi developing unique adaptations to support their interaction[2]. A recent study by Zhejiang University has uncovered new insights into such a mutualism involving mealybugs and the fungus Penicillium citrinum[1]. Mealybugs are significant agricultural pests that can cause extensive damage to crops. While it is known that beneficial fungi can aid insects in adapting to various environments, the specific locations and mechanisms of these interactions have remained elusive. This study reveals that mealybugs feeding on tomato plants develop a unique pellet-like structure on their legs, which houses P. citrinum. Interestingly, this structure does not form when mealybugs feed on other plants such as cotton, potato, or eggplant. The formation of these at-leg pellets is a collaborative process involving secretions from the host plant and waxy filaments produced by the mealybugs. Within these pellets, the researchers identified the presence of P. citrinum, a fungal strain that also colonizes the honeydew excreted by the mealybugs. This fungus plays a crucial role in protecting mealybugs by inhibiting fungal pathogens that could otherwise harm them. The compounds found within the pellets exhibit inhibitory activity against these pathogens, enhancing the survival rate of mealybugs under pathogen pressure. The study also found that the at-leg pellets provide additional benefits to the mealybugs. They increase the frequency with which the insects suck plant sap and reduce the defensive responses of the host plants, thereby facilitating easier feeding and greater nutrient intake for the mealybugs. This discovery ties into previous research on insect-fungus mutualisms. For instance, ambrosia beetles are known to carry fungal symbionts in specialized structures called mycangia, which help them farm these fungi as a nutritional resource[3]. Similarly, necrophagous beetles use antimicrobial secretions to regulate the microbial communities on carrion, creating a favorable environment for their larvae[4]. These examples illustrate how insects utilize fungi not only for nutrition but also for protection and environmental manipulation. The findings from the Zhejiang University study expand our understanding of these complex interactions by highlighting a novel mechanism through which mealybugs and P. citrinum interact. The at-leg pellets represent a unique adaptation that enhances the mealybugs’ ability to thrive in specific environments, similar to the specialized structures seen in other insect-fungus mutualisms. In conclusion, this study sheds light on the intricate relationships between mealybugs, fungi, and host plants. By forming at-leg pellets that house beneficial fungi, mealybugs can protect themselves from pathogens and manipulate their environment to their advantage. This research not only provides new insights into the coevolution of insect-fungi-plant interactions but also opens up potential avenues for developing strategies to manage mealybug infestations in agriculture.

BiochemAnimal ScienceMycology

References

Main Study

1) An at-leg pellet and associated Penicillium sp. provide multiple protections to mealybugs.

Published 16th May, 2024

https://doi.org/10.1038/s42003-024-06287-2

Related Studies

2) Ecology and Evolution of Insect-Fungus Mutualisms.

https://doi.org/10.1146/annurev-ento-011019-024910

3) Fungal mutualisms and pathosystems: life and death in the ambrosia beetle mycangia.

https://doi.org/10.1007/s00253-021-11268-0

4) Burying beetles regulate the microbiome of carcasses and use it to transmit a core microbiota to their offspring.

https://doi.org/10.1111/mec.14269


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