Tests for antibiosis and antixenosis resistance to Rhopalosiphum padi L., the bird cherry-oat aphid, were conducted among four wheat (Triticum aestivum L.) and eight triticale (XTriticosecale Wittmack) accessions. Tests for antibiosis included measuring R. padi-population growth over 13 days, number of days to reproduction of individual R. padi, and number of aphid progeny produced in the first 7 days of adulthood. Antixenosis was measured in no-choice nymphiposition tests and in choice tests of host selection by winged R. padi. Three of seven triticale accessions limited R. padi populations relative to control accessions. Lower R. padi-population growth on N1185 and Okto Derzhavina could be explained partially by increased developmental times. Lower R. padi-population growth on triticale accessions N1185, N1186 and Okto Derzhavina could be explained at least partially by fewer aphid progeny on these accessions. Developmental time of R. padi on N1185 and Okto Derzhavina was greater than that on Stniism 3 triticale, identified previously as resistant to R. padi. There were less R. padi progeny on N1185 than on Stniism 3, and comparable numbers of R. padi progeny among N1186, Okto Derzhavina, and Stniism 3. None of the accessions limited nymphiposition by R. padi. Choice tests revealed heterogeneity in host selection by R. padi but an overall trend that triticale accessions Okto Derzhavina, N1185, N1186 and Stniism 3 were less preferred hosts than Arapahoe wheat. Relatively strong resistance in these triticale accessions warrant consideration of their future use in breeding programs for cereal-aphid resistance.

The toxicity of imidaloprid to the migratory grasshopper, Melanoplus sanguinipes (F.), was measured in bioassays, greenhouse trials, and field trials. An LD50 of 53 and 86 ppm for the oral/topical applications of imidacloprid confirmed a low toxicity for this chemical when compared with carbofuran as a standard. However, 100% debilitation was observed at concentrations of > or = 1 ppm. Grasshoppers exhibited leg flexing, abdominal quivering, and tremors before becoming motionless and appearing dead. Knockdown was temporary with a high percentage of recovery within 1 h. Efficacy and feeding damage were determined from artificial infestations of M. sanguinipes at the 2nd, 4th, and early tillering growth stages of winter and spring wheat treated with foliar and seed treatments of imidacloprid. All rates of imidacloprid tested resulted in < 45% mortality to 4th instar and adult M. sanguinipes in the greenhouse and field. Although efficacy was low, high rates of debilitation in bioassays suggest that improved control may be gained by combining imidacloprid with insect pathogens or additional chemicals.

The toxicity of imidacloprid to the cereal leaf beetle, Oulema melanopus (L.), was measured under laboratory and field conditions. Insect mortality and plant damage were determined from artificial and natural infestations of O. melanopus applied to various growth stages of barley. All rates of imidacloprid formulated and applied as a seed treatment caused >90% mortality to cereal leaf beetle larvae when barley was infested with eggs at the 4-leaf stage, but were ineffective when barley was infested with eggs at the early tillering or flag-leaf stages of barley. This window of susceptibility influenced results obtained in field trials where peak larval emergence did not occur until the early tillering stage of barley. The resulting mortality in plants from treated seeds never exceeded 40% in the field. Foliar imidacloprid, however, caused >90% mortality in the field, and may be another option in the management of the cereal leaf beetle.

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Malting barley was planted by a producer located near Edgar, MT on 13 Apr. Plots were 20 ft long and 8 rows wide (1 ft row spacing) and arranged in a RCB design with four replications (Trial 1) and 3 replications (Trial 2). Insecticide applications were made using a backpack, CO2-powered sprayer equipped with TeeJet XR8002VS nozzles, calibrated to deliver 8.2 gpa at 30 psi. Number of CLB eggs and larvae per plant were counted on 3 plants from center rows. Plots in Trial 1 were treated on 17 May when barley was at 2 to 3 tiller stage and evaluated on 1,3, and 11 DAT. No CLB larvae were detected until 28 May. A second trial was conducted to determine insecticide efficacy on CLB larvae. Plots in Trial 2 were treated on 4 Jun when barley was beginning to joint and evaluated on 1,3, 7, and 14 DAT. Data were analyzed using ANOVA and means were separated using DMRT.