Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/28/2001
Publication Date: 8/1/2001
Citation: ALTRE, J.A., VANDENBERG, J.D. FACTORS INFLUENCING THE INFECTIVITY OF ISOLATES OF PAECILOMYCES FUMOSOROSEUS AGAINST DIAMONDBACK MOTH, PLUTELLA XYLOSTELLA. JOURNAL OF INVERTEBRATE PATHOLOGY. 2001. v. 78. p. 31-36. Interpretive Summary: The diamondback moth is a worldwide pest of cruciferous vegetables. Each year, farmers spend more than $1 billion to control this pest, primarily with chemical insecticides. However, many populations of diamondback moth have become resistant to conventional, as well as some biological, insecticides. Alternative control measures being investigated include the use of insect-pathogenic fungi, but basic studies of the conditions under which insects are susceptible to fungal infection are needed for effective control in the field. We tested whether changing any of three factors would alter the infectivity against diamondback moths of fungal strains. We found that pregermination of fungal spores improved infectivity for 3 out of 4 strains tested. For a strain that shows very low infectivity under normal conditions, we found that insect larvae starved for 3 days are more susceptible to infection and that insects maintained in conditions of high relative humidity are more susceptible to infection. These findings improve our understanding of the factors that make insects susceptible to fungi and will help us design effective strategies for their use as safe, biological control agents.
Technical Abstract: Paecilomyces fumosoroseus isolate 1576 was isolated from an insect, but is avirulent against larvae of diamondback moth, Plutella xylostella. Pregermination of conidia failed to increase infectivity of isolate 1576, but the procedure did increase infectivity of 3 other isolates. Isolates 1576 and 4461 were both more infective when moisture was high during incubation of inoculated larvae. Starved diamondback moth larvae were mor susceptible than fed larvae to isolate 1576 (40% and 10% mortality, respectively), but starved and fed larvae were similar susceptibility to isolate 4461. Isolate 1576 grew faster and produced more conidia than isolate 4461 on potato dextrose agar. These results suggest that isolate 1576 is a saprophyte that is generally unable to penetrate insect cuticle, but can sometimes infect larvae that are starved or otherwise stressed.