Thomas M. Mowry

Changes in green peach aphid responses to potato leafroll virus-induced volatiles emitted during disease progression.

ABSTRACT Previous research has shown that green peach aphids, Myzus persicae (Sulzer), preferentially settle on leaflets of potato plants (Solanum tuberosum L.) infected with potato leafroll virus (PLRV) compared with sham-inoculated controls, at least in part because of aphid responses to volatile cues from the plants. The prior work used plants 4 wk after inoculation. In this study, aphid emigration from the vicinity of leaflets of PLRV-infected plants at 2, 4, 6, 8, and 10 wk after inoculation was compared with emigration from leaflets of sham-inoculated control plants. For the bioassay, 30 aphids were placed directly above a test leaflet on screening to exclude gustatory and tactile cues and in darkness to exclude visual cues. The numbers emigrating were recorded every 10 min for 1 h. Volatile organic compounds (VOCs) were collected from the headspace of the test plants, quantified, and compared among treatments. In bioasssays with leaflets of upper nodes of the plants, aphid immigration rates were significantly lower from leaflets of PLRV-infected plants than from sham-inoculated plants at 4 and 6 wk after inoculation, but not at 2, 8, and 10 wk after inoculation. In bioassays with leaflets from lower nodes, emigration did not differ between PLRV-infected plants and shaminoculated plants at any stage in the infection. Volatile compounds detectable in the headspace of intact plants at 2, 4, and 8 wk after inoculation (or sham inoculation) changed with plant age and with disease progression, potentially explaining behavioral responses of the aphids.

Effects of sub‐lethal imidacloprid levels on potato leafroll virus transmission by Myzus persicae

The effects of sub‐lethal imidacloprid concentrations on acquisition and inoculation of potato leafroll virus (PLRV) by Myzus persicae (Sulzer) (Hemiptera: Aphididae) were investigated. In experiments using two aphid clones to acquire PLRV from infected potatoes, virus transmission declined significantly with increasing concentrations of imidacloprid. The same was true in experiments using imidacloprid‐treated Physalis floridana Rydb. as acquisition sources. When viruliferous M. persicae were placed on uninfected, imidacloprid‐treated P. floridana, there were significant declines in PLRV transmission. Sub‐lethal concentrations of imidacloprid clearly inhibited both acquisition and inoculation of PLRV by M. persicae, either through poisoning, temporary intoxication, and/or antifeedant effects.

Green Peach Aphid (Homoptera: Aphididae) Action Thresholds for Controlling the Spread of Potato Leafroll Virus in Idaho

Abstract Arbitrary green peach aphid, Myzus persicae (Sulzer), action thresholds (0, 5, 10, 20, and 40 aphids per 100 leaves) were tested in 3 yr of field experimentation to determine if they could be maintained and if they would significantly impact aphid densities and limit the incidence of potato leafroll virus (PLRV). In 1997 and 1998, significant linear relationships between thresholds and final percentage of PLRV (expressed as the percentage of tubers infected with PLRV) were observed; there was a trend toward lower PLRV incidence with decreasing action threshold in 1999. There were significant relationships between thresholds and mean number of apterous aphids in 1998 and 1999, indicating that reduction of PLRV resulted from reduced within-field spread by apterae. In almost all cases, aphid densities exceeded threshold levels from one week to the next, clearly showing that the thresholds could not be maintained. Over all experiments, four to nine seasonal applications of methamidophos were warranted by the magnitude of the threshold. Imidacloprid applied at planting to the zero aphid threshold reduced the number of methamidophos applications from nine in the insecticide-at-detection treatment to five. A revised within-field green peach aphid management plan is recommended that includes systemic insecticide applied at planting, aphid sampling every 3–4 d, and foliar insecticide application following aphid detection.

Influence of the Potato leafroll virus and virus-infected plants on the arrestment of the aphid, Myzus persicae

Abstract A series of experiments was conducted using membrane sachets containing MP148 diet or phosphate-buffered sucrose with and without purified Potato leafroll virus to determine if direct encounter with the virus would arrest the aphid, Myzus persicae (Sulzer) (Homoptera:Aphididae). In only two out of 36 tests were there significantly more aphids settled on sachets containing the virus. In all other tests, there were either significantly fewer aphids on sachets containing virus or there were no differences between virus treatments and control sachets without virus. In an experiment using excised Physalis floridana leaves, twice as many M. persicae settled on virus-infected leaves as on noninfected control leaves. Taken together, the results indicate that arrestment of M. persicae on potato leaf roll virus-infected plants may be due to enhanced nutritional qualities resulting from disease, but not from direct encounter with or detection of the virus.

Domyzus (nectarosiphon) species other thanm persicae pose a threat to the idaho potato crop

Green peach aphids (Myzus persicae (Sulzer) ) pose a threat to the Idaho potato (Solanum tuberosum L.) crop primarily because they transmit potato leafroll virus (PLRV). Only colonizing vectors are epidemiologically significant because PLRV is persistently transmitted. Additionally, Idaho winters are severe enough that most permanently anholocyclic aphid species do not establish. It is now accepted that the taxon that has been known asMyzus (Nectarosiphon)persicae (Sulzer) is in fact at least three species (M. persicae, Myzus nicotianae Blackman andMyzus antirrhinii (Macchiati) ). It was not known whether the newly designated species had the potential to damage the Idaho potato crop. The objectives of our research were to determine whetherMyzus (Nectarosiphon) spp. other thanM. persicae occurred naturally in Idaho, whether they could colonize potato and transmit PLRV, and whether they were potentially holocyclic.NoMyzus (Nectarosiphon) spp. other thanM. persicae were found in Idaho in trap nurseries; howeverMyzus ascalonicus Doncaster recently has been found on stored bulbs and in suction trap collections in north Idaho. Laboratory bioassays for PLRV vector potential usingPhysalis floridana Rydb. indicator plants show thatM. nicotianae can transmit PLRV as efficiently asM. persicae. Similarly,M. nicotianae colonized potato as well asM. persicae in a replicated laboratory experiment comparing two clones ofM. nicotianae and one clone ofM. persicae. Our observations indicate that North AmericanM. nicotianae may be capable of a limited facultative holocycle. Thus, in laboratory experiments,M. nicotianae is as damaging asM. persicae with respect to PLRV vector potential; however,M. nicotianae may not occur naturally in areas like Idaho that have no tobacco production. A summary of allMyzus (Nectarosiphon) spp. with respect to PLRV epidemiology is provided.CompendioLos áfidos verdes del melocotonero [Myzuspersicae (Sulzer) ] representan un problema para el cultivo de papa (Solanum tuberosum L.) de Idaho debido principalmente a que ellos transmiten el virus del enrollamiento de la hoja de la papa (PLRV). Sólo los vectores que constituyen colonias son epidemiológicamente significativos debido a que elPLRV es persistentemente transmitido. Adicionalmente, los inviernos de Idaho son suficientemente severos de manera a que la mayoría de las especies de áfidos permanentemente anholocíclicas no se establecen. Se acepta ahora que el taxon que fuera conocido comoMyzus (Nectarosiphon)persicae (Sulzer) representa por lo menos tres especies [M. persicae, Myzus nicotianae Blackman yMyzus antirrhinii (Macchiati) ]. No se conocía si las especies designadas recientemente tenían el potencial para dañar el cultivo de papa en Idaho. Los objetivos de la investigación fueron determinar si las especies deMyzus (Nectarosiphon) diferentes aMyzus persicae ocurren naturalmente en Idaho, si ellas pueden colonizar a la papa y transmitir el PLRV y si eran potencialmente holocíclicas.No se encontraron en los semilleros trampa, en Idaho, especies deMyzus (Nectarosiphon) diferentes alMyzus persicae, sin embargo, se ha encontrado recientemente en el norte de Idaho alMyzus ascalonicus Doncaster en bulbos almacenados y recolecciones en trampas de succión. Bioensayos de laboratorio para determinar el potencial de los vectores del PLRV, utilizandoPhysalis floridana Rydb. como planta indicadora, muestran queM. nicotianae puede transmitir el PLRV tan eficientemente como elM. persicae. Similarmente,M. nicotianae colonizó a la papa tan bien como elM. persicae en un experimento de laboratorio con repeticiones en el que se compararon dos clones deM nicotianae con un clon deM. persicae. Las observaciones indican que elM. nicotianae norteamericano puede ser capaz de un holociclo facultativo limitado. Así, an experimentos de laboratorio, elM. nicotianae es tan dañino como elM. persicae en relación al potencial como vector del PLRV; sin embargo,M. nicotianae puede no ocurrir naturalmente en zonas como Idaho en donde no se produce tabaco. Se presenta un resumen de todas las especies deMyzus (Nectarosiphon) en relación a la epidemiología del PLRV

Survey of Colorado potato beetle insecticide resistance in Idaho

Colorado potato beetle populations from Idaho were surveyed for resistance to carbofuran, endosulfan, esfenvalerate, and phosmet in a discriminating concentation bioassay of spring emergent and first generation adults. No carbofuran or endosulfan resistance was detected in 29 populations surveyed. Esfenvalerate and phosmet resistance was detected in all potato growing areas of the state. For the same populations, spring adults were more sensitive to phosmet than were first generation adults. Susceptible populations were found in the same regions as resistant populations.