Tritrophic interactions between an invasive weed (Lepidium latifolium), an insect herbivore (Bagrada hilaris), and a plant pathogenic fungus (Albugo lepidii)

Authors: TOFANGSAZI, NASTARAN - University Of California, Davis; Hogg, Brian; Portman, Scott; Pratt, Paul

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2019
Publication Date: 10/11/2019
Citation: Tofangsazi, N., Hogg, B.N., Portman, S.L., Pratt, P.D. 2019. Tritrophic interactions between an invasive weed (Lepidium latifolium), an insect herbivore (Bagrada hilaris), and a plant pathogenic fungus (Albugo lepidii). Environmental Entomology. 48(6):1317-1322. https://doi.org/10.1093/ee/nvz111.
DOI: https://doi.org/10.1093/ee/nvz111

Interpretive Summary: Perennial pepperweed is an invasive weed in the western U.S.A. that can form dense stands and outcompete native species. Few effective control methods are available for this weed. One promising option is biological control, which involves introducing a natural enemy from the weed's native range to help suppress populations of the weed. However, many crops plants in the cabbage family are closely related to perennial pepperweed, and would be at risk if a natural enemy was introduced. Several natural enemies of perennial pepperweed are already present in California, and may help control the weed. A fungus was discovered in California that appears to attack only perennial pepperweed, and a stinkbug, bagrada bug, attacks perennial pepperweed throughout much of California. Interactions between these two natural enemies may enhance or compromise biological control of perennial pepperweed. We investigated whether leaves infected with the fungus attract or repel bagrada bug, whether the presence of the fungus increases or decreases bagrada bug survival and development, and whether bagrada bug could transmit the fungus from plant to plant. Bagrada bug strongly preferred healthy over infected leaves, and infection by the fungus also lowered the survival of bagrada bug. Bagrada bug did not transmit the fungus between plants. These results suggest that the fungus and bagrada bug could work together to suppress perennial pepperweed, if bagrada bug focuses on healthy leaves. On the other hand, the presence of the fungus could cause bagrada bug to shift to other plants if infection rates are sufficiently high. More research is needed to explore these two possibilities in the field.

Technical Abstract: Perennial pepperweed, Lepidium latifolium L., is an invasive plant in the western U.S.A. that can form dense stands and displace native species. Currently no biological control agents are available for L. latifolium in U.S.A. A major obstacle to developing a classical biological control program targeting L. latifolium is the many closely related cruciferous vegetable crops that could be at risk from an introduced natural enemy. The plant fungal pathogen Albugo lepidii, first reported in the U.S.A. in 2008, produces white blister “rust” spots underneath the leaf surfaces of L. latifolium. Initial host range testing indicated high levels of host specificity, with L. latifolium the only known host. Bagrada hilaris (Hemiptera: Pentatomidae) is a serious economic pest of Brassicaceae vegetable crops that also feeds on L. latifolium, and may interact with A. lepidii to affect biological control of L. latifolium. Here we investigate effects of A. lepidii on B. hilaris preference and development, and of B. hilaris on A. lepidii infection. B. hilaris prefered healthy L. latifolium leaves compared to rust-infected leaves and feeding on infected leaves reduced B. hilaris survival. Our data demonstrated that B. hilaris could acquire the rust spores while feeding, but that it did not passively transmit the pathogen to healthy plants.