Progress 07/01/02 to 06/30/07
Outputs
Implementing biological control as part of an IPM program in Idaho: The 1st step in my IPM program was to identify and investigate potential natural enemies of Colorado potato beetle (CPB) and aphids in southeastern Idaho. With the use of pitfall traps, yellow pan traps, suction traps, and leaf counts, more than 12,000 arthropod individuals were collected, identified, and their relative frequency in plots treated with and without insecticides was assessed. The most significant difference between untreated and treated fields was the presence of carabid beetles in the untreated ones. 19 species of carabid beetles were identified; one of these, Pterostichus melanarius (Illiger), an introduced European species, accounted for 88 % of all individuals caught. Laboratory tests showed that P. melanarius responds to different aphid and CPB densities in a functional manner (the number of prey consumed per predator increases as prey density goes up). The carabid was observed
killing and feeding on all instars of CPB and 3 species of aphid vectors of potato viruses. Given the rate of consumption of eggs and the estimated rate of oviposition by the CPB, one P. melanarius adult could potentially stop the total reproductive potential of up to 5 CPB adults. P. melanarius could be a potential biological control agent of potato pests, and since is already present and abundant in southeast Idaho it could be used in conjunction with soft chemistries for the control of potato pests. The evaluation of weeds as potential inoculum sources for aphid-mediated transmission of Potato Leafroll Virus (PLRV): Even the most strict aphid control strategy may not prevent the spread of the two most important potato viruses, PLRV and Potato virus Y (PVY), unless measures also are taken to keep virus-source plants within and outside the crop at a minimum. My studies revealed that weeds, such as the hairy nightshade (HNS), Solanum sarrachoides (Sendtner), are an important inoculum
source of potato viruses and an excellent host for their aphid vectors. HNS is one of the 4 most prevalent weeds in Idaho. With the use of several molecular tools, we demonstrated that PLRV transmission from HNS to potato by the green peach aphid (GPA) is four times the transmission rate of potato to potato. Natural HNS PLRV infection in the field could be as high as 6%. Laboratory and field studies revealed a preference of aphids for HNS and for infected plants, and the involvement of visual, gustatory, tactile and olfactory cues in the response of aphids. Olfactory cues generated by HNS and also by virus infected plants attract and/or arrest aphids. Therefore, a low level of PLRV-hairy nightshade infection could enhance the disease spread in the field. We also found that mixed-viral infections of PVY and PLRV are a regular occurrence in Idaho's potato cropping systems. Laboratory studies show that the fecundity of the potato and GPA was significantly higher on mixed-infected plants
than on singly-infected plants or non-infected plants. Both winged and wingless potato and GPA preferentially settled on PVY-PLRV infected plants than on singly-infected plants or non-infected plants.
Impacts
Chemical companies are working in the production of new "softer" chemistries that could potentially improve the effect of natural enemies, such as P. melanarius. If the new chemistries could in fact prevent the disruption of natural balances in the crop ecosystems by selectively killing only the pest insects, we could potentially have a successful IPM program using soft insecticides and natural enemies at the same time. Pest control decisions using an IPM approach will help to reduce production costs by decreasing pesticide use. The final result of reduced pest control costs will be higher income for growers and reduced health risks for all people involved in crop management. Before this research, little was known about the involvement of HNS in aphid vector attraction and performance, and PLRV and PVY epidemiology. Higher disease transmission rates from HNS to potato than from potato to potato makes HNS an efficient inoculum source of PLRV. Increasing detection of
PLRV and PVY infections in the PNW potato fields over the last few years despite using high quality planting material supports our findings. This research will allow a more complete understanding of the interaction between viruses, and vectors, and aid in development of much needed and improved virus management plan. These results suggest that the basis of any virus reduction program in Idaho and the PNW should be reevaluated to place more emphasis on HNS control. Recommendation for nightshade control have been developed and published.
Publications
- Srinivasan, R. and Alvarez, J.M. 2007. Effect of mixed-viral infections (Potato virus Y-Potato leafroll virus) on the biology and preference of vectors, Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae). J. Economic Ent. in Press.
- Hamm, P., Boydston, R., Hoy, C.W., Hutchinson, P., Stevenson, W., Alvarez, J.M., Alyokhin, A., Boiteau, G., Dively, G., Gudmenstad, N. and Kirk, W. 2007. Managing pesticide resistance. In Potato Health Management D.A. Johnson ed. The American Phytopathological Society, St. Paul, MN. In press.
- Srinivasan, R., Alvarez, J.M., Eigenbrode, S. and Bosque-Perez, N. 2006. Influence of hairy nightshade Solanum sarrachoides (Sendtner) and Potato leafroll virus (Luteoviridae: Polerovirus) on the preference of Myzus persicae (Sulzer) (Homoptera: Aphididae). Environmental Entomology. 35:546-553.
- Alvarez, J.M., Menalled, F. and Hoy, M.A. 2006. Herramientas moleculares en el control biologico. Revista Manejo Integrado de plagas y Agroecologia. 16(6):249-252.
- Novy, R.G., Alvarez, J.M., Sterret, S.B., Kuhar, T.P. and Horton, D. 2006. Progeny of a tri-species potato somatic hybrid express resistance to wireworm in eastern and western potato production regions of the U.S. Am. J. Potato Res. 83:126.
- Alvarez, J.M. and Novy, R.G. 2005. Resistance to wireworms in different advanced potato selections in Idaho. 53rd Annual Meeting of the Entomological Society of America. Abstract of presented research may be found at: http://esa.confex.com/esa/2005/techprogram/paper_21408.htm.
- Alvarez, J.M. and Hutchinson, P.J.S. 2005. Managing hairy nightshade to reduce potato viruses and insect vectors. Outlooks on Pest Management Journal. 16(6):249-252.
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Progress 01/01/05 to 12/31/05
Outputs
1) Implementing biological control as part of an IPM program in Idaho: Several microcosmic preference and feeding assays were conducted with the objective of studying the predatory potential of P. melanarius on potato pests. Preference assays conducted with various life stages of Colorado potato beetle (CPB) (Leptinotarsa decemlineata; Coleoptera: Chrysomellidae) in the presence and absence of aphids revealed a preference for early instar CPB larvae and eggs when compared to late instars and adults. P. melanarius preferred aphids only after CPB larvae and eggs. In both cases, P. melanarius did not prefer adult CPB. Various instars of CPB and various species of virus vectoring aphids were also offered as preys. The rate of some different prey species attacked by P.melanarius showed a positive linear relationship with prey density. Therefore, a functional response to density of some potato pests killed by P.melanarius seems to be present. P. melanarius devoured as many
as 24 first 12 and second third and fourth instar CPB larvae /day and preyed on over 50 aphids/day Vine climbing experiment to study the behavioral suitability of P. melanarius to potato pests clearly revealed that P. melanarius could also climb the potato vine and actively forage for prey. 2) The evaluation of weeds as potential inoculum sources for aphid-mediated transmission of Potato Leafroll Virus (PLRV): The potential of Hairy nightshade, Solanum sarrachoides (Sendtner) as an aphid reservoir and virus source and its spread or perpetuation was investigated. With the use of DAS- ELISA, it was confirmed that green peach aphid can transmit PLRV to hairy nightshade and that aphids can become viruliferous after feeding on infected hairy nightshade plants. Transmission from hairy nightshade to potato is four times the rate of potato to potato or potato to hairy nightshade. The green peach aphid preferred hairy nightshade over potato plants and reproduced at a higher rate on hairy
nightshade than on potato. Settling bioassays with both winged and wingless green peach aphid revealed a preference for S. sarrachoides over potato and for PLRV-infected plants over non-infected plants of both species. Settling patterns of green peach aphid remained the same under both light and dark conditions, indicating that visual cues were not required for the observed response and other cues like gustatory, tactile and olfactory could be involved. Additional experiments confirmed the involvement of olfactory cues that attract and/or arrest green peach aphid, thereby influencing its preference for S. sarrachoides over potato and PLRV-infected over non-infected plants. Therefore, a low level of PLRV-hairy nightshade infection could enhance the disease spread in the field.
Impacts
The abundance, predatory potential and suitability of P. melanarius indicates the effectiveness of this beetle to reduce populations of potato pests and its potential to be used in an integrated pest management program in Idaho, together with cultural practices, host plant resistance, and selective pesticides. From field experiments, we have learned that the insecticide aldicarb drastically reduced populations of P. melanarius. Therefore, this insecticide should be avoided to promote the positive effect of this predator. Hairy nightshade plants can not only act as aphid reservoirs but also can be infected with PLRV. Higher disease transmission rates from hairy nightshade to potato than from potato to potato makes hairy nightshade an efficient inoculum source of PLRV and could explain the frequent outbreaks of PLRV in southeastern Idaho despite the use of high-grade seed at planting. The importance of hairy nightshade in the epidemiology of potato viruses is not unique
to Idaho. Our research contributes to the overall understanding of the role of S. sarrachoides in the potato-PLRV pathosystem and could be used to design more efficient PLRV disease management strategies. These results suggest that the basis of any PLRV reduction program in Idaho and the PNW should be reevaluated to place more emphasis on hairy nightshade control. Recommendation for nightshade control have been developed and published.
Publications
- Hoy, C.W., Boiteau, G., Alyokhin, A., Dively, G. and Alvarez, J.M. 2005. Managing insect pests. In APS Potato Health Management book. In Press.
- Alvarez, J.M., Menalled, F. and Hoy, M.A. 2005. Molecular tools in biological control. (in Spanish). Revista Manejo Integrado de plagas y Agroecologia. In Press.
- Alvarez, J.M. and Srinivasan, R. 2005. Evaluation of hairy nightshade as an inoculum source for the aphid-mediated transmission of potato leafroll virus. Journal of Economic Entomology. 98:1101-11008.
- Alvarez, J.M. 2004. Potato insect pests. In J.L. Capinera (ed.), Encyclopedia of Entomology. Klower Academic Press, 1803-1816.
- Menalled, F., Alvarez, J.M. and Landis, D. 2004. Molecular techniques, habitat management and parasitoid conservation in annual cropping systems. In: G. Gurr, S. Wratten and M.A. Altieri (Eds) Ecological Engineering: Advances in habitat manipulation for arthropods. CSIRO Press, 6:103-117.
- Novy, R.G., Alvarez, J.M., Corsini, D.L., Nasruddin, A., Radcliffe, E.B. and Ragsdale, D.W. 2004. Resistance to PVY, PLRV, PVX, green peach aphid, Colorado potato beetle, and wireworm in the progeny of a tri-species somatic hybrid. American Journal of Potato Research. 81 (1):77-78.
- Kuhar, T., Speese, P.J. III, Whalen, J., Alvarez, J.M., Alyokhin, A. and Ghidiu, G. 2003. Current status of insecticidal control of wireworms in potatoes. Pesticide Outlook. 14:265-267.
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Progress 01/01/04 to 12/31/04
Outputs
1) Implementing biological control as part of an IPM program in Idaho: We continued experiments with Pterostichus melanarius (Illiger), the predominant carabid species in Southern Idaho. The insect was again observed killing and feeding on all instars of CPB and aphids that are vectors of potato viruses. Research in 2002 and 2003 demonstrated that it is a well-established species in potato fields and could be an effective predator of CPB and aphids. We have developed an increase knowledge base on the behavior and predator attributes of P. melanarius. From field experiments, we have learned that fields where the insecticide aldicarb has been applied at planting presented lower number of P. melanarius than fields without the insecticide. Laboratory tests conducted with the objective of characterizing the attributes and effectiveness of P. melanarius showed that this beetle responded to different prey densities in a functional manner (the number of prey consumed per
predator increases as prey density goes up). These tests showed that P. melanarius could be a potential biological control agent of Colorado potato beetle and several species of aphids, and since is already present and abundant in southeast Idaho; it can be used in conjunction with more selective chemistries for the control of potato pests. In 2005, we will conduct laboratory experiments to evaluate the effect of new chemistries on P. melanarius and compare them with the organophosphate, pyrethroid and carbamate insecticides. 2) The evaluation of weeds as potential inoculum sources for aphid-mediated transmission of Potato Leafroll Virus (PLRV): Research results revealed that green peach aphid (GPA) can transmit PLRV from hairy nightshade to potato and transmission rate from the weed to potato is greater than from potato to potato. An increase in GPA reproduction on hairy nightshade compared with reproduction on potato also was observed. In addition, laboratory and field experiments
demonstrated that GPA preferred hairy nightshade over potato. Also, GPA preferred PLRV infected hairy nightshade or potato plants compared with uninfected plants, with plant volatiles as possible attractants. Otherwise, little is known about the involvement of hairy nightshade in GPA attraction and performance, and PLRV epidemiology. The current PNW PLRV and GPA management plan is not always effective and calls for expensive and environmentally challenging control measures. Field trials conducted in southern Idaho indicated that nightshade plays an important role in the PLRV epidemiology and the presence of the weed in potato plots increases the amount of aphids and consequently the amount of virus infection. We are currently investigating the hairy nightshade plant factors, such as volatile attractants, compared with potato plant factors influencing GPA.
Impacts
The EPA is in the process of re-registering pesticides under the requirements of the FQPA, and could eventually cancel some or all OP, and carbamate pesticides on potatoes. The alternative could be the use of more selective pesticides, which could potentially maximize the effectiveness of biological control agents such as P. melanarius. The beetle is abundant in southeast Idaho and could be used in conjunction with selective chemistries for the control of potato pests. Once growers adopt this research, the total chemical input could be reduced. Saving even one pesticide application per year would result in a substantial savings to growers and would greatly reduce the use of OPs. PLRV, one of the most important viruses of potato, is transmitted most efficiently by green peach aphid (GPA). GPA and other aphids have been identified as the potato pest most frequently targeted for pesticide applications in the U. S. primarily due to their role as virus vectors.
Insecticides are moderately-effective at reducing virus transmission. Even the most intense aphid control may not prevent spread of PLRV unless measures are also taken to keep virus-source plants at a minimum. Nightshade weeds also may become infected with PLRV. This may explain why, even with pesticide usage, there have been potato seed lot rejections of >50% by state seed certification agencies due to high levels of viruses in the lot. This research will allow a more complete understanding of the interaction between the weeds, virus, and vector, and aid in development of much needed and improved management plan.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
1) Implementing biological control as part of an IPM program in Idaho: The first step in my IPM program was to identify and investigate potential natural enemies of Colorado potato beetle (CPB) and aphids in southeastern Idaho. After two years of field experiments it was determined that Pterostichus melanarius (Illiger), an introduced European species, is the predominant species in southeastern Idaho accounting for 88 % of all individuals caught and also that CPB damage appeared to be less severe in the fields where newer insecticides had spared populations of P. melanarius. Laboratory tests showed that P. melanarius responds to different aphid and CPB densities in a functional manner (the number of prey consumed per predator increases as prey density goes up). The carabid was observed killing and feeding on all instars of CPB and three species of aphid vectors of potato viruses. Given the rate of consumption of eggs and the estimated rate of oviposition by the CPB,
one P. melanarius adult could potentially stop the total reproductive potential of three to five CPB adults. 2) The evaluation of weeds as potential inoculum sources for aphid-mediated transmission of Potato Leafroll Virus (PLRV): PLRV is one of the most serious aphid-transmitted diseases that affect yields and quality of potatoes. The green peach aphid (GPA) is considered to be by far the most effective vector of this virus. Even the most intense aphid control may not prevent spread of PLRV unless measures are also taken to keep virus-source plants at a minimum. Nightshades are one of the four most prevalent weeds in Idaho and are one of the preferred weed hosts for GPA. Laboratory and field experiments demonstrated an increased preference of GPA to hairy nightshade over potato, an increased preference of PLRV-infected plants over non-infected plants and also that host preference of GPA remained the same under light and dark conditions, confirming the original hypothesis of an
involvement of olfactory cues in host selection. The final objective of this research is to isolate what is attracting the aphids, so we could potentially use that as a trap. 3) The optimization of insecticide applications to reduce virus transmission in the field: All insecticides treatments reduced aphid numbers significantly from the untreated checks through the entire study period in Russet Burbank fields (this virus susceptible variety is planted in more than 75% of the potato acreage in Idaho). Although plots treated with aldicarb and methamidophos presented higher number of alate GPA than plots treated with more selective chemistries at two different dates, these differences were not significant. However, these insecticides do not prevent virus transmission because they do not prevent other infected aphids flying from nearby fields. Besides, when OPs are eventually lost as a control option due to the FQPA, growers will have to transition to other pest control chemicals. ELISA
data is being processed to determine the amount of virus transmission for each treatment.
Impacts
According to the Food Quality Protection Act, broad-spectrum insecticides, especially the organophosphates, will be eventually eliminated from the market. Growers in Idaho and the Pacific Northwest will have to find alternatives to these insecticides. The alternative could be the use of more selective pesticides, which could potentially maximize the effectiveness of biological control agents of potato pests. P. melanarius could be a potential biological control agent of potato pests, and since is already present and abundant in southeast Idaho, it can be used in conjunction with soft chemistries for the control of potato pests. Once growers adopt this research, the total chemical input could be reduced. Saving even one pesticide application per year would result in a substantial savings to growers and would greatly reduce the use of organophosphates. For virus management, even the most intense aphid control may not prevent spread of PLRV unless measures are also taken
to keep virus-source plants at a minimum.
Publications
- Alvarez, J.M., R.L. Stoltz, C.R. Baird, and L.E. Sandvol. 2003. Insect pests and their management. In: Love S. and J. Stark (eds.) Potato Production Systems 12: 204-239.
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Progress 01/01/02 to 12/31/02
Outputs
Implementing biological control as part of an IPM program in Idaho: In efforts to identify and investigate potential biological control agents in potato fields, an inventory of natural enemies occurring in southeastern Idaho was conducted. Coleopterans dominated the complex of ground arthropods and Pterostichus melanarius (Pm), an introduced European carabid species, represented 88 % of all individuals caught. We have developed an increase knowledge base on the behavior and predator attributes of Pm. Field plots where the insecticide aldicarb had been applied at planting presented the lowest number of Pm. The highest populations of Pm coincide with the time when mature Colorado potato beetle (CPB) larvae of the 1st generation and adults of the summer generation are present in potato fields. Unfortunately, application of foliar pyrethroid insecticides against CPB also reduced the populations of Pm. Laboratory tests conducted with the objective of characterizing the
attributes and effectiveness of Pm found that adults of this beetle kill and feed on all instars of CPB, green peach aphid (GPA), potato aphid, and bird cherry oat aphid, and respond to different densities in a functional manner (the number of prey consumed per predator increases as prey density goes up). These tests showed that Pm could be a potential biological control agent and since is already present and abundant in southeast Idaho, it can be used in conjunction with soft chemistries for the control of potato pests. Evaluating weeds as an inoculum source for the aphid-mediated transmission of PLRV: GPA is the most effective vector of Potato leafroll virus (PLRV), one of the most serious diseases that affect yields and quality of potatoes. Nightshades are one of the preferred weed hosts for GPA. We found that reproduction of GPA on the weed is up to 50 % higher than on potatoes. We recorded early infestations of aphids along the edges of potato fields and observed colonies on
nightshades before detecting any aphid on potato plants. Laboratory experiments showed that nightshades become infected with PLRV at the same rate as potatoes and that GPA can transmit the virus from nightshade to a potato plant. Six % of nightshade plants from the field were found positive for PLRV and in few cases for other viruses such as PVY and PVX. Most of the infected nightshades were located in a field planted with a high amount of infected potato seed as inoculum source. Optimizing insecticide applications to reduce PLRV transmission in the field: Field experiments found that most insecticides treatments reduced aphid numbers significantly from the untreated checks through the entire study period. However, they might not prevent virus transmission because they do not stop other infected aphids flying from nearby fields. We will test tubers from each insecticide treatment (all and new chemistries) to determine the amount of virus transmission for each treatment.
Impacts
According to the Food Quality Protection Act, broad-spectrum insecticides, especially the organophosphates, will be eventually eliminated from the market. Growers in Idaho and the Pacific Northwest will have to find alternatives to these insecticides. The alternative could be the use of more selective pesticides, which could potentially maximize the effectiveness of biological control agents of potato pests. This research will identify effective natural enemies in Idaho that could be compatible with new selective pesticides. The final result of less insecticides usage would be reduced pest control costs and consequently a higher income for growers and reduced health risks for all people involved in crop management. Saving even one pesticide application per year would result in a substantial savings to growers and would greatly reduce the use of organophosphates. Our program will utilize grower-cooperators as the primary outreach component, complemented with a web site
and traditional extension outreach programs such as the Potato Schools and commodity publications. For virus management, even the most intense aphid control may not prevent spread of PLRV unless measures are also taken to keep virus-source plants at a minimum. We are currently caution growers to keep their nightshade well in check, especially in seed-growing areas where disease prevention is essential.
Publications
- Alvarez, J.M. 2002. Another alternative. Beetle power: fighting bug to bug. Potato Grower. June- 28-29.
- Alvarez, J.M., N. Matteson, and M. Wiebe. 2002. Biological control in the potato crop in Idaho. 44th Idaho Academy of Science meeting proceedings. 45.
- Stoltz, R. L., C. R. Baird, and Alvarez, J.M. 2002. PNW Beneficial organisms associated with Pacific Northwest crops. Extension publication PNW 343.
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