Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

The effects of nine bermudagrass, Cynodon dactylon (L.) Pers., varieties and strains on the development, survivorship, consumption and utilization, preference, and host suitability of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) were determined. The bermudagrasses tested were 'Coastal', 'Tifton 44', 'Tifton 78', 'Tifton 292', 'Grazer', #1 R12P5, 'OSU 71 X 6-7','OSU 74 X 11-2', and 'OSU 74 X 12-1'. 'Tifton 292' was the most preferred grass by neonate larvae, while 'OSU 74 X 11-2' was the least preferred grass. 'Tifton 78' was the most susceptible host, while 'OSU 71 X 6-7' was the least suitable host to FAW based on a host suitability index. The bermudagrasses were grouped as susceptible ('Tifton 78', 'OSU 74 X 12-1', and 'Grazer'), intermediately resistant (#1 R12P5, 'Coastal', 'Tifton 292', 'OSU 74 X 11-2', and 'Tifton 44'), or resistant ('OSU 71 X 6-7') to FAW. The mechanism of resistance in 'OSU 71 X 6-7' to FAW appears to be antibiosis rather than nonpreference. Another study evaluated the development and survivorship to the adult stage of FAW on 'Coastal', 'Grazer', 'Tifton 292' and 'OSU 71 X 6-7' bermudagrasses grown in the field and greenhouse. Bermudagrasses grown in the greenhouse were more suitable to the development of FAW than grasses grown in the field. Larvae reared on greenhouse grown grasses showed significantly (P $<$ 0.05) higher larval and pupal weights in the three trials and required less time to develop. Grasses grown in the greenhouse had significantly (P $<$ 0.05) higher quality than grasses grown in the field. The quality of the field grown grasses declined more rapidly from June to September than did greenhouse grown grasses. A two-year field experiment was undertaken to determine the impact of varying densities of FAW on 'Coastal' and 'Alicia' bermudagrasses. Artificial infestations of FAW at densities of 1.1 to 9.9 larvae per 0.1 m$\sp 2$ caused yield losses that ranged from 0.5 to 1.5 metric ton per ha for 'Coastal' and 0.3 to 0.9 metric ton per ha for 'Alicia'. Fall armyworm feeding on 'Coastal' also resulted in crude protein and digestible dry matter yield losses of ca. 72 and 245 kg/ha, respectively. Significant (P $>$ 0.05) differences in quality and yield could not be detected in 'Alicia'. The economic injury level of 'Coastal' was 8 fourth and fifth instar larvae per 0.1 m$\sp 2$, while the economic threshold was 4 fourth and fifth instar larvae per 0.1 m$\sp 2$.

Pages

151

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