Aphid Alert 1999, No. 13, September 8

Summer 1999: Aphid trapping data

Results reported in this issue of Aphid Alert are total captures of winged aphids and species identifications for the following locations and sampling interval end-dates. At some locations the potato crop has been harvested. If additional data is received for locations not reported on this page (no data) that data be incorporated into this week's issue of the newsletter once the samples have been received and sorted.

3 September Figure 1 (below). Mean number of winged green peach aphid captured per trap across all locations reported, 1998 data (blue line) and 1999 data (maroon line). These data are also available in table format (Table 1). Figure 2 (below). Mean number of winged aphids of species known to be capable of transmitting PVY (exclusive of green peach aphid) captured per trap across all locations reported, 1998 data (blue line) and 1999 data (maroon line). These data are also available in table format (Table 1).

Summary of Observations for Week Ending 8 September

Green peach aphids per trap averaged just 0.55 per trap during the week ending 8 September. Other aphids species which can vector PVY averaged 8.00 per trap. Thus, aphid numbers are lower than last week, and especially so for green peach aphid which was down 73%. Today, trap capture data is reported for only 9 of the 14 stations in the network. Missing data will be added to this WWW report as it becomes available and associated files will be updated accordingly. PCR data for green peach aphids captured during the week ending 2 September is also not yet available.

Last week, heavy rains were widespread. Some locations where we have traps received 3 or more inches of rain. Not only was the weather unfavorable for aphid flight, but some of the traps filled with water probably resulting in some loss of aphids that had been captured. Given the prevalence of late blight and the dire consequences of the wet weather, aphids probably were not the most immediate concern of most potato growers. However, the aphid and virus situation may be better than we earlier expected.

In early summer 1999, green peach numbers were considerably higher than on the same dates last year, but for the past two weeks numbers have been lower than last year. Over all dates, green peach aphid captures per trap are 49.4% higher than in 1998. Captures of PVY vectors other than green peach aphid are down 75.5% from 1998.

This summer, we have yet to detect our first PLRV-positive green peach, whereas last year 59% of green peach aphids captured in August 1998 were positive for PLRV. Our PCR tests have also been negative for PVY. PVY. However, IC-PCR data for PVY may less useful because PVY is non-persistent in the aphid, so non-detection only means that that aphid was not infected when captured. The data for PLRV is greater biological significance, because an aphid once infected with PLRV remains so for life.

Table 2. IC-PCR test results for week ending 30 August

Our most abundant potential PVY vector in 1999 has been turnip aphid, which reproduces on canola. A search of the literature has not provided much information as to the importance of this aphid as a PVY vector. This species is known to transmit PVY, but it appears that its efficiency as a vector is not established.