The Biology and Ecology of the Bromegrass Seed Midge in Nebraska

These studies indicate that smooth bromegrass, Bromus inermis Leyss, is the only host of the bromegrass seed midge, Stenodiplosis bromicola Marikovskiy and Agafonova, in Nebraska. The midge did not infest two common annual brome species under field conditions. The midge has been collected from all counties surveyed in Nebraska and seems to be widely distributed throughout the midwestern states. An apparently undescribed species of Tetrastichus (Hymenoptera: Eulophiclae) was observed to parasitize all stages of the bromegrass seed midge. Parasitism rates greater than 90% were observed. The parasite larvae do not kill the midge until damage to the bromegrass floret has occurred. However, a high parasite population may help to reduce the population of the bromegrass seed midge in succeeding generations

Seasonal Population Fluctuations and Natural Control of the Sweetclover Aphid

Because the potential of the sweetclover aphid for damaging sweetclover is well documented, yet damage occurs only occasionally under field conditions, it would appear that natural factors which depress midsummer populations are important in preventing greater damage and worthy of detailed study. Thus, this study was begun early in 1959 to investigate the natural factors which generally keep populations of this aphid below levels causing economic damage

Studies of the Mechanisms and Sources of Spotted Alfalfa Aphid Resistance in Ranger Alfalfa

Mechanisms and sources of spotted alfalfa aphid resistance in Ranger alfalfa and its five parental strains were investigated during 1957-1960

Identification of QTL for resistance and susceptibility to Stagonospora meliloti in autotetraploid lucerne

In eastern Australia and California, USA, one of the major lethal fungal diseases of lucerne (Medicago sativa) is Stagonospora root and crown rot, caused by Stagonospora meliloti. Quantitative trait loci (QTL) involved in resistance and susceptibility to S. meliloti were identified in an autotetraploid lucerne backcross population of 145 individuals. Using regression analysis and interval mapping, we detected one region each on linkage groups 2, 6 and 7 that were consistently associated with disease reaction to S. meliloti in two separate experiments. The largest QTL on linkage group 7, which is associated with resistance to S. meliloti, contributed up to 17% of the phenotypic variation. The QTL located on linkage group 2, which is potentially a resistance allele in repulsion to the markers for susceptibility to S. meliloti, contributed up to 8% of the phenotypic variation. The QTL located on linkage group 6, which is associated with susceptibility to S. meliloti, contributed up to 16% of the phenotypic variation. A further two unlinked markers contributed 5 and 8% of the phenotypic variation, and were detected in only one experiment. A total of 517 simple sequence repeat (SSR) markers from Medicago truncatula were screened on the parents of the mapping population. Only 27 (6%) SSR markers were polymorphic and could be incorporated into the autotetraploid map of M. sativa. This allowed alignment of our M. sativa linkage map with published M. truncatula maps. The markers linked to the QTL we have reported will be useful for marker assisted selection for partial resistance to S. meliloti in lucerne