Doctor of Philosophy (PhD)



Document Type



Sugarcane in Louisiana is colonized and sometimes heavily infested by two aphid species, the sugarcane aphid, Melanaphis sacchari (Zehntner), and the yellow sugarcane aphid,Sipha flava(Forbes). Melanaphis sacchari, the main vector of sugarcane yellow leaf virus, is distributed throughout Louisiana’s sugarcane-growing regions. Five cultivars representing 90% of the commercial acreage in Louisiana (LCP 85-384, HoCP 91-555, Ho 95-988, HoCP 96-540,L 97-128) were evaluated for resistance to aphids in the greenhouse. Antibiosis was the primary category of resistance to both aphid species. Based on the intrinsic rate of natural increase, L 97-128 and HoCP 91-555 were comparatively susceptible and resistant cultivars, respectively. In plant and ratoon cane field experiments, the fewest number of aphids occurred on HoCP 91-555,indicating resistance under field conditions. Melanaphis sacchari was more abundant than S.flava in both plant and ratoon cane. Laboratory studies indicated that Diomus terminatus(Coleoptera: Coccinellidae) could have additional role in managing M. sacchari. Categories of resistance were also assessed by studying the feeding behavior of M. sacchari on LCP 85-384, HoCP 91-555, and L 97-128 using the electrical penetration graph technique. Differences among cultivars were not detected in the time interval that aphids initiate sieve element feeding; however, M. sacchari ingested phloem sap of L 97-128 twice as long as on HoCP 91-555. Differences between L 97-128 and HoCP 91-555 were not detected in levels of total phenolics and available carbohydrates, and in water potential. Free amino acid analyses of phloem sap extracts indicated that two essential amino acids (histidine and arginine) were absent in the phloem sap of HoCP 91-555. Analyses of honeydew collected from aphids feeding on both cultivars showed that two free essential (leucine and isoleucine) and two free nonessential (tyrosine and proline) amino acids were absent in the honeydew of aphids feeding on HoCP 91- 555. These studies suggest that the absence of particular free essential amino acids in the phloem sap of HoCP 91-555 and inability of M. sacchari to derive specific free essential and nonessential amino acids are underlying mechanisms responsible for reduced feeding time and lower growth potential on this cultivar.



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Committee Chair

Reagan, Thomas E.



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Entomology Commons