Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2005
Publication Date: 1/3/2006
Citation: Jackson, M.A., Erhan, S., Poprawski, T.J. 2006. Influence of formulation additives on the desiccation tolerance and storage stability of blastospores of the entomopathogenic fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes). Biocontrol Science and Technology. 16(1/2):61-75. Interpretive Summary: 'Yeast-like' blastospores of the bioinsecticidal fungus Paecilomyces fumosoroseus (Pfr) infect numerous soft-bodied insects including whiteflies, aphids, and subterranean termites and are being developed as a non-chemical control for these serious insect pests. Fantesk is a starch:oil composite that can incorporate various additives and form a stable aqueous suspension upon rehydration. In these studies, various compositions of Fantesk were tested as formulates for blastospores of Pfr with the goal of improving the storage stability, suspension stability, and biocontrol efficacy of this biological control agent. These studies showed that Fantesk composites containing sucrose and whole milk significantly improved the ability of blastospores of Pfr to survive freeze-drying and remain viable for up to one year during cold storage. Blastospore suspensions also demonstrated improved suspension stability when formulated with Fantesk. Improved suspension stability keeps blastospores in suspension longer thus ensuring uniform coverage during spray application. The infectivity of Pfr blastospores against the silverleaf whitefly was not improved by formulation but was also not significantly reduced compared to the standard blastospore formulation tested. Further studies directed at understanding how formulation additives impact the ability of blastospores to infect their insect host are needed. These studies have shown that stable, dry formulations of Pfr blastospores can be produced using appropriate formulation technology thus improving their commercial potential for use as a non-chemical pest control agent.
Technical Abstract: Blastospores of the bioinsecticidal fungus Paecilomyces fumosoroseus were formulated with 10% lactose/1% bovine serum albumin (BSA) or various compositions of Fantesk(TM), a starch-oil composite prepared by jet-cooking an aqueous dispersion of starch and oil. Blastospore formulates were evaluated for storage stability as wet or freeze-dried preparations, for efficacy in infecting and killing silverleaf whitefly nymphs, and for dispersion and stability as aqueous suspensions. Storage stability studies with wet blastospore formulates showed that maximum blastospore survival was achieved during low-temperature storage at -20C with lactose/BSA formulates or Fantesk formulates supplemented with zein protein, sucrose, and whole milk. Under conditions of wet storage at -20C, the addition of whole milk to Fantesk formulates significantly improved blastospore stability while the addition of sucrose or zein protein had no effect. When blastospores were formulated with lactose/BSA or Fantesk formulates with zein protein, sucrose, and whole milk prior to freeze-drying, no significant differences were seen in blastospore desiccation tolerance or in stability during storage at either 4C or -20C. Freeze-dried blastospore formulates stored at 4C showed no significant loss in blastospore viability after 3 months' storage and blastospore formulates stored at -20C showed no significant loss in viability during the 12-month study. For freeze-dried Fantesk formulations, the addition of sucrose was shown to improve blastospore survival during the freeze-drying or desiccation process. The addition of whole milk to Fantesk formulations significantly improved the stability of freeze-dried blastospores stored at 4C. The LD90 dosage rate for blastospores of P. fumosoroseus formulated with lactose/BSA or Fantesk formulates supplemented with zein protein, sucrose, and whole milk were not significantly different in bioassays using 3rd instar nymphs of the silverleaf whitefly (Bemisia argentifolii). In addition, all formulates tested produced blastospore suspensions that remained stable for up to 2 hours after mixing. The blastospore concentration in unformulated blastospore suspensions were significantly reduced due to settling after standing for only 30 minutes. These results suggest that formulates can be used to improve the desiccation tolerance, storage stability, and dispersion characteristics of blastospores of this promising bioinsecticide.