Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

A method for screening rice, Oryza sativa L., germplasm for resistance to the fall armyworm, Spodoptera frugiperda (J. E. Smith), was developed. Infesting rice seedlings grown in the greenhouse proved to be an efficient method to identify sources of resistance. In the evaluation of over 5,000 rice accessions, moderate resistance to S. frugiperda larval defoliation was detected in plant introductions 160842, 346830, 346833, and 346853. Moderate levels of resistance were also detected in the United States cultivars 'Honduras', 'Newrex', and 'Chinese'; and in O. glaberrima Steud accessions 101800, 102554, and 369453. Effects of S. frugiperda feeding on rice were studied in the field during 1983 and 1984. Increased infestation levels resulted in increased defoliation, reduced plant and panicle density, and reduced rice yields. Yield component studies indicated that lower yields on infested plots were the result of reduced plant and panicle densities and reduced panicle size. Kernel weight and filling were not affected. Yield reductions were found to be linearly related to S. frugiperda larval density. The linear model E(y) = b x(,1) accounted for a large proportion of the variance of yield during both years. Twenty-eight parasitoid adults, larvae, and puparia were recovered from S. frugiperda larvae collected from rice fields in Puerto Rico. Eight were identified as Lespesia sp. (Diptera:Tachinidae), and one as Archytas mormoratus (Townsend), (Diptera:Tachinidae). The fungus Nomuraea rileyi (Farlow) Sampson killed eight larvae and three were infected by an unidentified microsporidium. Development, longevity, and reproduction of S. frugiperda from Louisiana (LA) and Puerto Rico (PR) were evaluated in larvae reared on artificial diet and rice foliage. At egg hatch, larvae of PR origin were smaller than LA larvae. Differences in neonate larval size were also evident at the other stages of development, but did not extend to adult longevity or reproductive parameters. Larvae, pupae and adults of the LA strain were heavier and completed development in a shorter period of time than the PR strain. Differences are probably under genetic control and may indicate some degree of reproductive isolation.

Pages

130

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