Submitted to: Mycopathologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 2003
Publication Date: September 1, 2004
Citation: Lord, J.C., Howard, R.W. 2004. A proposed role for the cuticular fatty amides of Liposcelis bostrychophila (Psocoptera: Liposcelidae) in preventing adhesion of dry-conidia entomopathogenic fungi. Mycopathologia 158: 211-217. Interpretive Summary: Book lice or psocids are increasingly problematic contaminants in stored grain and grain products. In previous work, we found that psocids bear a unique profile of cuticular lipids that includes the only fatty amides known to occur in insects. We showed that psocids are highly tolerant of insect pathogenic fungi. We tested major components of the cuticular lipids to determine if they had anti-fungal activity. None of the lipids found on the psocids inhibited germination or growth of either of the two most important fungal pathogens of insects, but the fatty amide appears to limit adhesion of spores to insect surfaces. Spore adhesion to the fatty amides did not differ from adhesion to psocid cuticles. Treatment of larval sawtoothed grain beetles with fatty amide reduced spore adhesion to the level that occurred on psocids. Understanding insects' defenses against diseases helps to develop strategies for deploying pathogens to control insect pests and protect beneficial insects.
Technical Abstract: Maximum challenge exposure of Liposcelis bostrychophila to Beauveria bassiana, Paecilomyces fumosoroseus, Aspergillus parasiticus or Metarhizium anisopliae resulted in no more than 16% mortality. We investigated several of L. bostrychophilas cuticular lipids for possible contributions to its tolerance for entomopathogenic fungi. Saturated C14 and C16 fatty acids did not reduce the germination rates of B. bassiana or M. anisopliae conidia. Saturated C6 to C12 fatty acids that have not been identified in L. bostrychophila cuticular extracts significantly reduced germination, but the reduction was mitigated by the presence of stearamide. Cis-6-hexadecenal did not affect germination rates. Mycelial growth of both fungal species did not occur in the presence of caprylic acid, was reduced by the presence of lauric acid, and was not significantly affected by palmitic acid. Liposcelis bostrychophila is the only insect for which fatty acid amides have been identified as cuticular components. Stearamide, its major fatty amide, did not reduce germination of B. bassiana or M. anisopliae conidia or growth of their mycelia. Adhesion of conidia to stearamide preparations did not differ significantly from adhesion to the cuticle of L. bostrychophila. Pretreatment of Oryzaephilus surinamensis larvae with stearamide significantly decreased adhesion of B. bassiana or M. anisopliae conidia to their cuticles. Cuticular fatty amides may contribute to L. bostrychophila's tolerance for entomopathogenic fungi by decreasing hydrophobicity and static charge, thereby reducing conidial adhesion.