Development of economic thresholds for pea aphid (Hemiptera: Aphididae) management in lentil (Fabaceae) based on in-field insecticide efficacy trials.

Pea aphid (Acyrthosiphom pisum Harris, Hemiptera: Aphididae) presents a significant economic challenge to lentil (Lens culinaris Medik.) production in the major growing region of Saskatchewan, Canada. During 2019-2020, field experiments were conducted to optimize the management tools for pea aphid control on lentils. A randomized split-plot design was used with main plots consisting of different pea aphid pressures and subplots consisting of different insecticide treatments. The main plot design was aimed to assess the impact of A. pisum feeding on lentil yields during the late vegetative to early reproductive stages. Subplots of the study evaluated the efficacy of 3 insecticides in suppressing pea aphid populations on lentils. Lentil is susceptible to A. pisum feeding and requires management at low pest densities. The economic threshold for pea aphids on lentil crops varied depending on environmental conditions, ranging from 20 to 66 aphids per sweep, calculated using a discrete daily growth rate of 1.116. The estimated economic thresholds provided a 7-day lead time before aphid populations achieved the economic injury level (EIL). The EIL was defined as 78 ± 14 aphids per sweep net sample or 743 ± 137 cumulative aphid days from the first aphid present in the field. In addition, the results of the study found that, on average, foliar applications of insecticides containing the pyrethroid active ingredient lambda-cyhalothrin (IRAC group: 3A) reduced pea aphid populations by 83% compared with untreated control.

Detection and Identification of a 'Candidatus Liberibacter solanacearum' Species from Ash Tree Infesting Psyllids.

'Candidatus Liberibacter' species are associated with severe, economically important diseases. Nearly all known species are putatively insect transmitted, specifically by psyllids. Detection of 'Ca. Liberibacter' in plants is complicated by their uneven distribution in host plants and largely fastidius nature. The death of black (Fraxinus nigra) and mancana (Fraxinus mandshurica) ash trees in Saskatchewan, Canada has been associated with infestation by the cottony ash psyllid (Psyllopsis discrepans). A combination of conventional PCR amplification and Sanger sequencing of the 16S recombinant DNA was used to detect and identify 'Ca. Liberibacter' in psyllids collected from ash trees in Saskatchewan. BLAST analysis of two 16S sequences that were 1,058 and 1,085 bp long (NTHA 5, GenBank accession number MK942379 and NTHA 6, GenBank accession number MK937570, respectively) revealed they were 99 to 100% similar to a 'Ca. Liberibacter solanacearum' sequence (GenBank accession number KX197200) isolated from the Nearctic psyllid (Bactericera maculipennis) of U.S. provenance. Sequencing the psyllid genes CO1 and Cyt-b confirmed that the psyllids from which the bacterial DNA was isolated were P. discrepans, based on comparisons with sequences in GenBank and BOLD and a reference sample from the United Kingdom. These results provide the first evidence that 'Ca. Liberibacter solanacearum' species are associated with psyllids collected from ash trees and specifically P. discrepans. The recent episodes of dieback of ash in Saskatchewan associated with psyllid feeding are consistent with disease symptoms caused by 'Ca. Liberibacter' pathogens, and this possibility warrants further study.