Population development of the green peach aphid and beneficial insects in potato fields in British Columbia

Abstract

AbstractUsing 4 years of potato monitoring data containing insect counts, population development of the green peach aphid (Myzus persicae (Sulzer)) (Hemiptera: Aphididae), ladybird beetles (Harmonia axyridis (Pallas) and Coccinella septempunctata L.) (Coleoptera: Coccinellidae), and hymenopterous aphid parasitoids is described and used to consider revisions to current sampling plans. Depending on the year, field monitoring for aphids commenced between early May and early June. Aphid populations typically increased after 1 July and fluctuated until the end of the monitoring period (September). Winged M. persicae began to appear in sweep-net samples in late May, well in advance of the detection of aphids in visual samples. Aphid counts from field edge and interior sample sites were correlated and edge population levels were slightly and significantly greater than interior levels over the period 10 June – 14 July in 2 of the 4 years analyzed, suggesting a mild but inconsistent edge effect approaching mid season. Using an action threshold of 1 aphid/leaf to restrict the aphid-mediated spread of potato leaf roll virus (PLRV), the earliest whole-field action threshold was exceeded during 18–24 June in 1997. Using an action threshold of 10 aphids/leaf to address aphid-induced yield loss in fields not at risk to PLRV, the earliest whole-field action threshold was exceeded during 16–22 July in 1997. Therefore, monitoring for aphids can begin much later than the time it is currently commenced. A case is presented for monitoring only the edges of potato fields for an action threshold of 10 aphids/leaf, as interior samples rarely exceeded this action threshold when edge samples were below. This would further reduce the effort in sampling potato fields for aphids. Population development of ladybird beetle adults and larvae showed peaks occurring at different times during the growing season, depending on the year. Parasitism of aphids by hymenopterans occurred at low to moderate levels throughout the growing season (13% of total aphids in visual samples, on average), with peak parasitism appearing toward the end of the growing season in each year.