Progress 10/01/01 to 09/30/05
Outputs
We conducted a series of laboratory, greenhouse, and field experiments to investigate locomotory behavior of potato aphids (Macrosiphum euphorbiae (Thomas)), buckthorn aphids (Aphis nasturtii Kaltenbach), or green peach aphids (Myzus persicae (Sulzer)). All three species of potato-colonizing aphids were capable of surviving off host plants for 24-48 hours and walking on the soil surface between potato plants. Potato aphid, which is the largest in size, was the most mobile of the three species. The green peach aphid was intermediately mobile, and the buckthorn aphid was the least mobile species. Ten percent of potato aphids dispersed between potato plants in the absence of any environmental disturbance, with most of them moving onto plants located within the same row with the plant of their origin. This suggests that they employ the "bet-hedging" strategy distributing population in space. When forcibly removed from the host plant and released on the soil surface, all
three species colonized the nearest plant within one hour. However, when given no other choice, a significant proportion of aphids was fully capable of colonizing potato plants as far as 180 cm away from the point of release. After potato canopies closed later in the season because of plant growth, aphid dispersal increased and they became more evenly distributed among the plants. Environmental perturbations like wind, rain, and mechanical raking encouraged aphid movement, with the effect being more pronounced on larger plants with overlapping canopies. Regardless of canopy overlap, most aphids moved within the rows of potato plants. However, there was also considerable movement between the rows, even though the aphids had to walk over the surface of bare soil. Density of colonizing aphids along an artificial gradient created by insecticide applications did not affect PVY transmission within experimental plots. However, during one year of the experiment, significantly fewer tubers
were infected in the plots treated with foliar imidacloprid formulation than in plots treated with in-furrow formulation. It is possible that foliar imidacloprid applications in our study disrupted virus acquisition by non-colonizing aphid vectors.
Impacts
Currently, most management decisions are made based on the aphid abundance and/or on the proportion of aphid-infested plants. However, if aphids feed on the same plant for their entire life, even relatively high populations will not result in significant virus transmission. Alternatively, even a small population of highly mobile aphids can infect a large number of potato plants. Improved understanding of within-field aphid dispersal will allow fine-tuning control techniques, so that they are directed towards disrupting aphid movement, not just towards reducing aphid numbers. Proper timing of insecticide applications to eliminate aphids that are about to engage in interplant movement (rather than all aphids) may significantly reduce the amount of chemicals necessary for successful crop protection.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Potato aphids (Macrosiphum euphorbiae (Thomas)) used in the study were taken from the colonies currently maintained in our laboratory. They were originally collected from potato fields at Aroostook Experiment Farm in Presque Isle, Maine. The aphids were maintained in culture for no more than one year to prevent possible genetic shift due to adaptation to artificial laboratory conditions. We focused our most recent research efforts on the dispersal of the potato aphid because of its abundance and relatively high mobility. We were particularly interested in environmental stimuli that might promote early season aphid movement between potato plants. Aphid movement was observed in large arenas inside a greenhouse. Greenhouse arenas contained field-collected soil and simulated a small segment of a potato field. Their more detailed description is provided in my previous report that covered the first year of this project. Aphids were released on the central plant in the arena
and, after an initial settling down period, exposed to the following environmental disturbances: mechanical raking, simulated wind, simulated rain, increased lighting of the lower leaf surface, presence of a predator (adult lady beetle, Harmonia axyridis), fungicide application, and undisturbed control. None of the disturbances significantly encouraged aphid movement. However, between 10 and 17% of released aphids did move between the plants. Of those, up to one-third moved between the rows. Therefore, we may conclude that wingless potato aphids are fairly well adapted to withstanding environmental disturbances without falling off potato plants. In the same time, some of them moved between the plants even in the absence of such disturbances, possibly as part of the "bet-hedging" strategy distributing population in space. We also investigated the role that olfaction may play in host finding by potato aphids. Experiments were conducted in a Y-shaped olfactometer in our laboratory. Both
winged and wingless aphids responded positively to potato foliage odor. Of the 100 wingless aphids tested, 55 moved towards the source of potato odor, while only 24 aphids moved towards the odorless side of the olfactometer. A similar trend was noticed with the winged aphids, where 48 aphids moved towards foliage side, but only 25 aphids moved towards the odorless side. The remaining aphids engaged in very little movement and stay close to the point of their release in the olfactometer.
Impacts
A better understanding of aphid movement will allow more efficient management of viral outbreaks within potato fields. If aphids do not move between potato plants, their presence does not by itself indicate that control actions are necessary. This, in turn, will result in reduced insecticide use by commercial growers.
Publications
- Alyokhin, A. and G. Sewell. 2003. On-soil movement and plant colonization by walking wingless morphs of three aphid species (Homoptera: Aphididae) in greenhouse arenas. Environmental Entomology 32: 1393-1398.
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Progress 10/01/02 to 09/30/03
Outputs
Potato aphids (Macrosiphum euphorbiae (Thomas)), green peach aphids (Myzus persicae (Sulzer)), and buckthorn aphids (Aphis nasturtii Kaltenbach) used in the study were taken from the colonies currently maintained in our laboratory and originally collected from potato fields at Aroostook Experiment Farm in Presque Isle, Maine. Aphid survivorship on the surface of bare soil away from their host plants was tested in small arenas inside an environmental chamber. Each arena consisted of a clear plastic Petri dish lid, half filled with field-collected soil. The soil was moistened daily. To prevent aphid escape, the dish was covered by a clear ventilated plastic container. The container was turned upside-down and fitted inside the dish. In experimental arena, ten adult aphids were placed on the top of the soil using a camel hair brush. In control arena, ten adult aphids were placed on an excised potato leaflet inserted in a small plastic vial filled with tap water. Aphids
were checked for signs of life every 24 hours by visual observations and gentle probing with a soft camel hair brush. Aphid ability and propensity to move on the surface of bare soil was tested in larger arenas inside a greenhouse. Greenhouse arenas contained field-collected soil and simulated a small segment of a potato field. Their more detailed description is provided in my previous report that covered the first year of this project. During the first experiment, we investigated the propensity of wingless aphids to emigrate from potato plants. The aphids were released on the central plant in the arena, and the number of individuals moving on the surrounding plants was determined 48 hours later. During the second experiment, we released aphids on top of the soil either 90 cm or 180 cm from a row of potato plants, and then determined the number of individuals colonizing the plants during 48 hours following their release. On average, aphids survived 1.16 days (SE=0.04) on the surface
of bare soil; all of them dying within three-days. Wingless aphids did not leave potato plants that were adequate as a food supply. However, when given no other choice, a significant proportion of aphids was fully capable of colonizing potato plants as far as 180 cm away from the point of release. Potato aphid, which is the largest in size, was the most mobile of the three species. The green peach aphid was intermediately mobile, and the buckthorn aphid was the least mobile species. We also continued field experiments assessing relative contribution of colonizing and non-colonizing aphids to potato virus Y (PVY) transmission. Small potato plots each containing 5% of PVY-infected plants were left untreated with insecticides and open to the inflow of non-colonizing aphids. Population densities of non-colonizing aphids were monitored using green tile traps. Population densities of colonizing aphids were monitored by weekly visual observations. Tubers from each plot were harvested at the
end of the season and stored for further assessment of PVY infection and its correlation with aphid densities in experimental plots.
Impacts
A better understanding of aphid movement will allow more efficient management of viral outbreaks within potato fields. If aphids do not move between potato plants, their presence does not by itself indicate that control actions are necessary. This, in turn, will result in reduced insecticide use by commercial growers.
Publications
- Alyokhin, A. and G. Sewell. 2002. On-soil movement and plant colonization by walking wingless morphs of three aphid species (Homoptera: Aphididae) in greenhouse arenas. Accepted by Environmental Entomology, in press.
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Progress 10/01/01 to 09/30/02
Outputs
Our first experiment investigated aphid ability to move on the soil surface between the rows of potato plants. Three experimental arenas each consisting of a wooden box filled with field-collected soil have been constructed in the greenhouse. Eight 3-week old potted potato plants were arranged in three rows (two rows of three plants on the sides and one row of two plants in the middle) inside the arena. The pots were sunk to the brim into the soil. Plants within the side rows were spaced 20 cm apart, and the plants within the middle row were spaced 50 cm apart. Distance between the rows was 90 cm. Such an arrangement reflected approximate plant and row spacing in commercial potato fields in Maine. The arenas were enclosed in a Saran screen cage with a transparent plastic roof. Two laboratory-reared potato aphids (Macrosiphum euphorbiae (Thomas)), buckthorn aphids (Aphis nasturtii Kaltenbach), or green peach aphids (Myzus persicae (Sulzer)) were released in the center
of the arena. Each species was released into its own arena separately from other species. Released aphids were observed for 1 hour, or until they colonized one of the plants in the arena, or until they climbed up the arena wall. Experiment was repeated 12 times, with a total of 24 aphids of each species tested. None of the aphids moved between the rows in our experiments. Eighty-three percent of potato aphids, 67% of green peach aphids, and 58% of buckthorn aphids colonized plants with the middle row where they were released. Potato aphid was the most mobile species, and it took it the least amount of time to locate and colonize the plants. Greenhouse data were verified in large-walk-in field cages. The central plant in each cage was artificially infested with aphids, and then the proportion of aphids leaving the plants of their origin was monitored. The study was repeated three times during the growing season (early in the season soon after potato emergence from the soil, in
mid-season right before canopy closure, and late in the season after the canopy closure). The majority of aphid movement before the canopy closure took place within the rows, although occasional movement between the rows was also observed. Potato aphid was again the most mobile of the three potato-colonizing species. After the row closure, aphids became more evenly distributed among the plants. We also conducted a field experiment to assess relative contribution of colonizing and non-colonizing aphids to potato virus Y (PVY) transmission. We created different population densities of colonizing aphids by treating potato plots with different concentrations of imidacloprid. All plots were open to the inflow of non-colonizing aphids. Density of colonizing aphids did not affect PVY transmission within experimental plots. However, significantly fewer tubers were infected in the plots treated with foliar imidacloprid formulation than in plots treated with in-furrow formulation. It is
possible that foliar imidacloprid applications in our study disrupted virus acquisition by non-colonizing aphid vectors.
Impacts
A better understanding of aphid movement will allow for more efficient management of viral outbreaks within potato fields. If aphids do not move between potato plants, their presence does not by itself indicate that control actions are necessary. This, in turn, will result in reduced insecticide use by commercial growers.
Publications
- Alyokhin, A., G. Sewell, and E. Groden. 2002. Aphid abundance and potato virus Y transmission in imidacloprid-treated potatoes. American Journal of Potato Research 79: 255-262.
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