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Efficacy of the natural enemies of the greenbug, Schizaphis graminum (Rondani), in Texas High Plains grain sorghum
The efficacy of greenbug, Schizaphis graminum (Rondani), natural enemies was determined in grain sorghum using mechanical exclusion techniques and paired comparison experimental approaches. Indirect methods of evaluation including regression procedures and life table analyses were employed for comparison of efficacy evaluation methodologies. Greenbug emigration was shown to be progressively more important in causing declines in greenbug density as the growing season advanced. Dispersal of larval hymenopterous parasites within emigrating alate greenbugs and corn leaf aphids, Rhopalosiphum maidis (Fitch), also increased as the season progressed. Age structure of apterous greenbug forms was stable during periods of rapid density increase. Environmental conditions did not differ significantly between cages excluding natural enemies and those allowing enemy access in direct evaluation experiments. Greenbug densities on plants in cages excluding natural enemies rapidly exceeded established economic threshold levels and killed plants. Greenbug densities on plants in cages that allowed natural enemy access remained far below threshold levels. Significant increases in greenbug density on plants in these latter cages occurred only after the grain crop reached the soft dough stage of development and was probably not affected thereafter by aphid feeding. Predators provided a higher level of control than parasites throughout most of the study and increased to high densities in the absence of greenbug by feeding on corn leaf aphid. The coccinellids Hippodamia convergens (Guerin-Meneville) and H. sinuata (Mulsant) were responsible for greenbug suppression as determined by selective exclusion of these predators. Data did not show significant parasite activity during mid-season when greenbug is capable of rapidly exceeding the economic threshold level. Regression analyses indicated a significant (P = 0.05) relationship between coccinellid and greenbug densities. These analyses also show a positive relationship between corn leaf aphid and coccinellid densities, indicating a supportive role for corn leaf aphid in maintaining predator densities. Application of various correlation and regression procedures, as well as construction of variable, time-specific life tables, contributed results in strong agreement with those from direct evaluation of natural enemy efficacy. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI
1984 Dissertation K92
Diseases and pests
Kring, T. J. (1984). Efficacy of the natural enemies of the greenbug, Schizaphis graminum (Rondani), in Texas High Plains grain sorghum. Texas A&M University. Texas A&M University. Libraries. Available electronically from
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