Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2001
Publication Date: 11/1/2001
Citation: ALTRE, J.A., VANDENBERG, J.D. COMPARISON OF BLASTOSPORES OF TWO PAECILOMYCES FUMOSOROSEUS ISOLATES: IN VITRO TRAITS AND VIRULENCE WHEN INJECTED INTO FALL ARMYWORM, SPODOPTERA FRUGIPERDA. JOURNAL OF INVERTEBRATE PATHOLOGY. 2001. v. 78. p. 170-175. Interpretive Summary: Control of caterpillar pests of vegetables costs farmers billions of dollars every year. However, many pests 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 process of fungal infection are needed for effective control in the field. We evaluated the growth and infection of two strains of the insect-pathogenic fungus named Paecilomyces fumosoroseus. We found that spores of a more virulent strain germinate more quickly and are more readily grown in culture. We also found that, under most conditions, this virulent strain kills its insect host more quickly and at lower dosages. However, older larvae are equally susceptible to the two strains we evaluated. We showed that even when the virulent strain does not kill its host, it can delay its normal development. 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: Blastospore germination speed and production rate were compared in vitro between two isolates of Paecilomyces fumosoroseus. Virulence of blastospores of the two isolates was compared after injection into larvae of the fall armyworm, Spodoptera frugiperda. Blastospores of less virulent isolate 1576 are smaller than those of isolate 4461, and they germinate and dproliferate more slowly in vitro. The infectivity of injected blastospore of isolate 1576 against fall armyworm varies with larval size. In small larvae, percentage mortality was lower among those injected with isolate 1576 than among those injected with isolate 4461. Large larvae were equally susceptible to both isolates. Those larvae injected late in development that ultimately died, regardless of treatment, did not lose weight typical of developing pupae. Injection of large larvae with isolate 4461 resulted in a significantly longer time to pupation even though infection was not observed.