Post-application field persistence and efficacy of Cordyceps javanica against Bemisia tabaci

Authors: WU, SHAOHUI - University Of Georgia; TOWES, MICHAEL - University Of Georgia; Behle, Robert; BARMAN, APURBA - University Of Georgia; SPARKS, ALTON - University Of Georgia; Simmons, Alvin; Shapiro Ilan, David

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2023
Publication Date: 8/5/2023
Citation: Wu, S., Towes, M.D., Behle, R.W., Barman, A.K., Sparks, A.N., Simmons, A.M., Shapiro Ilan, D.I. 2023. Post-application field persistence and efficacy of Cordyceps javanica against Bemisia tabaci. The Journal of Fungi. 9/827. https://doi.org/10.3390/jof9080827.
DOI: https://doi.org/10.3390/jof9080827

Interpretive Summary: Whiteflies are serious pests of various vegetable and row crops. Various levels of whitefly control can be achieved using chemical insecticides. However, due to environmental and regulatory concerns, alternative methods of pest control are needed. Insect-killing fungi (also called entomopathogenic fungi) are safe environmentally friendly biopesticides that are used to control a variety of economically important pests. Previously, we discovered a new strain of entomopathogenic fungus called Cordyceps javanica Wf GA17. In laboratory studies, the new fungus strain killed whiteflies better than fungal biopesticides that are commercially available. However, the viability of the fungi under field conditions needed to be tested. In this study, we tested the persistence of the Wf GA17 fungus and a commercially available fungus strain (Apopka97) in cotton and snap bean fields. The fungi did not persist well initially so an oil formulation was added to enhance survival. The Wf GA17 strain caused whitefly mortality over a 14 day period and declined thereafter. Nonetheless, fungal persistence still requires improvement under field conditions as fungal spores declined rapidly, even after 24 h. . Future studies will be directed to improved formulation development and enhancing spray coverage to improve spore persistence and control levels in open field and controlled environments (such as greenhouses).

Technical Abstract: Previously, Cordyceps javanica Wf GA17 (a new strain of an entomopathogenic fungus causing natural and widespread epizootics among whiteflies in southern Georgia) demonstrated superior temperature tolerance and higher virulence against the whitefly Bemisia tabaci than commercial strains in the laboratory. The post-application persistence and efficacy of this fungus against B. tabaci was compared with the commercially available C. javanica Apopka97 strain over a two-year field study in cotton and vegetable crops. When blastospores of both strains were applied alone, whitefly populations were not effectively suppressed, although there were up to 17% mycosis occurrence in immatures. Thus, JMS stylet oil was added to fungal treatments for enhancing efficacy and persistence. For cotton leaves collected immediately after application, all fungal treatments caused similar but significant levels of immature mortality regardless of fungal strain, propagule form (conidia vs. blastospores), and application method (alone or mixed with JMS) except that Apopka97 blastospores caused higher mycosis levels than Wf GA17 alone. Wf GA17 blastospores + JMS incurred the highest mortality and mycosis levels at 7 days and reduced whitefly numbers for 14 days, but the efficacy declined thereafter. The JMS oil alone caused significant mortality and suppressed whiteflies. There was over 90% decline in the number of colony forming units 24 h after treatment in all fungal treatments. Across evaluation times, there was no difference between the two fungal strains (conidia or blastospores, alone or combined with JMS), but conidia had better persistence than blastospores for both strains; JMS oil enhanced persistence of Apopka97 but not Wf GA17 blastospores.