INTEGRATED PEST MANAGEMENT OF INSECT VECTORED PLANT VIRUSES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1017472
• Project Start Date: Sep 6, 2018
• Project End Date: Jul 31, 2022
• Program Code: [(N/A)]- (N/A)

Recipient Organization
LOUISIANA STATE UNIVERSITY
202 HIMES HALL
BATON ROUGE,LA 70803-0100

Performing Department
Entomology

Non Technical Summary
Preventing transmission of arthropod-vectored plant viruses involves knowing more than the virus, the host, and the permissive environment. Without a vector, most plant viruses would not be efficiently spread. There is an intimate relationship between viruses,plant hosts, andvector organisms. Understanding these trophic relationships is crucial to reducing/eliminating virus transmission. Simply using insecticides to eliminate vectors does not eliminate virus transmission and in some cases, may increase transmission rates. Historically, control of virusdissemination has been through seed certification to ensure virus-free seed and use of pesticides (insecticides and crop oils) to control vectors. However, vector control is of limited benefit becausemobile vectors cantransport viruses from distantsources.Non-persistently transmitted viruses can be acquired and spread in feeding probes within a few seconds duration andinsecticides cannot kill quickly enough to prevent transmission. Persistently transmitted viruses are more complex, involving extended periods of feeding and a 24-36hincubation between acquisition and ability to transmit. Insecticides can be of benefit, but not if the arrivingvectors are already capable of transmission. A holistic approach must include seed certification programs (reduce inoculum sources), roguing, spatial and temporal isolation, vector population monitoring, crop oils, barrier crops, and host plant resistance. However, before this can be accomplished, information on vector species and biology must be wellunderstood. Thus, the goal of current virus epidemiology research should be to prevent virus infection anddistribution through better understanding of landscape, environmental, and multi-trophic interactions between the virus, vector and host in order to create an integrated pest management plan.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
211	1549	1130	17%
216	1549	1170	16%
211	1450	1130	17%
216	1450	1170	16%
211	1520	1130	17%
216	1520	1170	17%

Knowledge Area
211 - Insects, Mites, and Other Arthropods Affecting Plants; 216 - Integrated Pest Management Systems;

Subject Of Investigation
1450 - Sweet potato; 1549 - Wheat, general/other; 1520 - Grain sorghum;

Field Of Science
1130 - Entomology and acarology; 1170 - Epidemiology;

Keywords

aphid

virus vector epidemiology

vector efficiency

Goals / Objectives
In Louisiana, insect vectored plant viruses have the potential for annual losses in sweetpotato and wheat of $21 million.Removing either the pathogen or the vector will prevent disease, preserving yields and reducing economiclosses due to quality issues. Unfortunately, a new virus vector has become widespread in Louisiana. The sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), which has now become a major pest of grain sorghum from southern Texas to Tennessee, has the potential to alter regional virus vector epidemiology. Because the potential loss to Louisiana agriculture from insect vectored viruses is great, this project will focus on understanding the multi-trophic impacts viruses and hosts can have on vector movement, feeding behavior, and population dynamics and will generate the necessary information critical to improve overall virus vector IPM. The following objectives are proposed: 1) Objective 1. Determine aphid alate densities in selected fields and surrounding landscapes. Each week, 20 plants will be randomly selected and total number of apterae and alatae will be identified to species and counted per plant (leaves, stem, and grain head, if present). Plant height and growth stage will be noted. If aphid numbers become too high to be quickly for accurate sampling in the field, leaves will be excised, individually bagged, placed in a cooler and returned to the laboratory for counting. Based on counts and planting densities, mean number of alates per week per acre will be determined. Counts as affected by week, and host plant will be compared using ANOVA. In combination with climatic data, this will give us a phenological model to accurately predict the number of virus vectors emigrating per acre per day.; 2) Objective 2. Determine aphid landing rates and species diversity in selected fields. Aphids will be trapped using yellow sticky traps (total population counts) and water pan traps (species identification purpose) throughout the year in sorghum, sugarcane, sweetpotato, and wheat (research stations and commercial producer farms) in Louisiana. A minimum of three fields per crop will be monitored. Traps will be changed weekly. A standard yellow sticky trap of dimensions 7.5 x 12 cm with double-sided adhesive (Whitemire Micro-Gen Research Laboratories Inc. St Louis, MO) will be set at plant canopy height. Three sets of yellow and green pan traps will be placed on a transect running diagonally from one corner of the field to the far corner. Insects on sticky traps will be counted with the aid of a stereo microscope (Bausch and Lomb, Rochester, NY). Pan trap contents will be brought to the laboratory, sorted, and preserved in 1.5 ml vials containing 95% ethanol for identification. Aphids will be identified to species or genus level using identification keys.; 3)Objective 3. Determine aphid vector efficiencies of key crop potyviruses and luteoviruses. Sugarcane aphid vector efficiency studies will determine acquisition, retention, and transmission of key plant pathogens of the crops listed above and will be compared to three other aphid vectors listed above. In sweetpotato, we will investigate vector efficiencies of SPFMV, SPVC, SPVG, and SPV-2. In wheat, we will investigate vector efficiencies of the BYDV/CYDV. In sorghum, we will investigate vector efficiencies of SrMV and BYDV/CYDV. In sugarcane, ScYLV vector efficiencies will be studied. To ascertain if M. sacchari can acquire a virus, aphids in groups of 5, 10, or singly will be given a 2 h pre-acquisition fast after which they will be confined in a 1.5-cm-diam clip cage on the abaxial surface of an inoculum source and allowed an acquisition access period (AAP) of 5 min (potyviruses) to 24 hr (luteoviruses). Aphids will be removed and placed into 1.5 ml microcentrifuge tubes and stored at -80°C. Viral RNA will be extracted and virus detected by RT-PCR. For persistently transmitted viruses, tests will be conducted to ascertain if M. sacchari can retain plant pathogens over time. Once the AAP is complete, M. sacchari will be placed in 1.5-cm-diam clip cage on the abaxial surface of a leaf of a virus free test plant that is not a host for the virus. Insects will be held in clip cages for 72 and 144 h, giving sufficient time for any virus particles to be purged from their digestive systems. Insects will be removed and placed into 1.5 ml microcentrifuge tubes and stored at -80°C. Viral RNA will be extracted and detected by RT-PCR. Transmission efficiency tests will be conducted as described above for pre-acquisition fast and AAP. Viruliferous M. sacchari will be given an inoculation access period (IAP) of 15 min (potyviruses) to 24 hr (luteoviruses). Insects will be manually removed and test plants will be soil treated with imidacloprid (Marathon 1% G, 0.02 g a.i./pot) and placed in a greenhouse for 2 wks for symptom development.4)Objective 4. Evaluate the impacts key crop potyviruses and luteoviruses have on host suitability, population dynamics, and feeding behavior of important aphid vectors. To determine host suitability and population dynamics of insect vectors on virus infected and virus free test plants, single adults will be transferred to each host, confined throughout the experiment in a 1.5-cm-diam clip cage on the abaxial surface of a leaf, and life table studies will be conducted for each virus and each vector. Single adults will be transferred to each host (sorghum, sugarcane, wheat, and sweetpotato), confined throughout the experiment in a 1.5-cm-diam clip cage on the abaxial surface of a leaf, and life table studies will be conducted for each virus and each vector, a minimum of three replicates, 50 aphids per replicate. Aphids will be allowed to larviposit for 12 h. After nymphs are deposited, the adult and all but a single first instar will be removed from each cage. Test plants will be placed in black 28 cm x 56 cm plastic plant trays in plant growth chambers held at 20 ± 0.2°C, 50 ± 5% RH and a photoperiod of 16:8 (L:D). Cohorts will be checked daily. Age (x), age-specific survival (lx), days to reproductive adult (DTRA), and number of progeny per female per day (mx) will be recorded, and age-specific fecundity (lxmx) calculated. Intrinsic rate of increase (rm) will be calculated using the equation of ∑e-rxlxmx = 1, net reproductive rate (R0) will be calculated as R0 = ∑ lxmx, mean generation time (T) will be calculated as T = ln(R0)/rm, finite rate of increase (λF) will be calculated as λF = erm, and doubling time (DT) will be calculated as DT = ln(2)/rm. Standard errors for all life table parameters and 95% CI will be calculated using the Jackknife procedure.

Project Methods
To compare vector probing behavior, electrical penetration graph (EPG) experiments will be conducted iFour test plants (2 virus-free, 2 infected) will be placed randomly within the Faraday cage. Next, one insect per test plant will then be placed on the abaxial side of a leaf and feeding behavior will be recorded for 4 h. This was repeated 20 times. Pre-probe, xylem phase (G), E1 (sieve element salivation), and E2 (phloem sap ingestion) durations were recorded per 4 h feeding bout.

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:The target audience for the project research outputs are other researchers, producers, and policy makers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project trained one postdoc this year. How have the results been disseminated to communities of interest?This project generated outputs in the form of research presentations presented at regional and national meetings and four published peer-reviewed journal articles. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? First, field movement of aphids was examined to identify trends in vector abundance throughout the sweetpotato growing season. Aphid abundance at the sites sampled appears to reflect the population dynamics of the most commonly collected species, the non-vector Melanaphis sacchari. Headspace volatiles of sweetpotato were collected to determine if virus infection status had an effect on the sweetpotato volatile profile. Thirteen compounds were produced by virus tested sweetpotato and 21 compounds were produced by infected sweetpotato. Compounds induced by virus infection were mainly green leaf volatiles and terpenes, many of which affect insect behavior. Additionally, this was the first recorded effort to identify volatiles from sweetpotato free of known diseases. Green peach aphid (GPA) preferred the odor of infected plants over virus tested plants, and the odor of virus tested plants and methyl salicylate (MESA) over the odor of virus tested plants alone. GPA preferred the odor of virustested plants alone over that of plant and methyl jasmonate (MEJA) or plant and neem oil. Settling assays were performed to determine if these preferences had any effect on aphid settling behavior. While GPA preferred plants treated with MESA, contrary to the result of the Y-tube assays, aphids preferred to settle on virus infected plants and neem oil treated plants over virus tested plants. This suggests that orientation towards odors does not necessarily indicate settling preference in GPA. The effect of headspace volatiles on aphid feeding on infected and virus tested sweetpotato was examined in order to determine if volatile treatments that do not directly affect the plant affect aphid feeding behavior. Both GPA and cotton aphid exhibited changes in behaviors related to virus transmission in the presence of all volatile treatments compared to controls when feeding on both virus tested and virus infected plants, suggesting that exposure to headspace volatiles while feeding affects aphid feeding behavior. However, in virus transmission assays, exposure to these volatiles during feeding did not affect the number of plants showing virus symptoms, suggesting that the changes in behavior are too subtle to affect transmission rates. We found that transmission of SrMV differs among two aphid species; M. sacchari and M. persicae. M. sacchari failed to transmit SrMV both singly and in groups under laboratory conditions. Studies of feeding behavior by EPG suggested that by virtue of producing higher numbers of probes during feeding, a longer potential drop duration with longer subphases II-1 and II-3, higher number of archlets during subphase II-3, and lower time to produce first potential drops than M. sacchari, M. persicae possesses an ability to successfully transmit SrMV from sorghum to sorghum. We conducted greenhouse and laboratory experiments to determine the effects of Cucumber mosaic virus or Sunn-hemp mosaic virus infected cowpea on soybean looper and fall armyworm larval growth and adult oviposition preference. We found that both viruses did not affect soybean looper larval growth. However, fall armyworm larvae benefitted upon feeding on CMV-infected cowpea leaves in our studies. In the oviposition preference study, we observed that soybean looper and fall armyworm adults preferred to lay more eggs on the healthy plants as compared to the virus-infected ones. We conducted lab experiments to understand if BPEV-infection provides any benefit to bell pepper hosts against a common pest, M. persicae. We designed experiments to determine preference behavior, host suitability and population dynamics of M. persicae on BPEV-infected and non-infected pepper plants. Through host preference bioassays, we found that M. persicae preferred virus-free leaves as compared to virus infected ones. This could indicate that BPEV infection might have benefitted the host by making them unattractive to the vector herbivores and could be reducing virus inoculation of non-persistent viruses. Moreover, we also found that BPEV negatively affected longevity and fecundity of aphids. The findings of this study provide an important first step towards understanding the complex interaction that occur between BPEV, bell pepper and M. persicae.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Wilson, B. E., Reay-Jones, F. P. F., Lama, L., Mulcahy, M., Reagan, T. E., Davis, J. A., Yang, Y. and Wilson, L. T. 2020. Influence of sorghum cultivar, nitrogen fertilization, and insecticides on infestations of the sugarcane aphid (Hemiptera: Aphididae) in the southern United States. J. Econ. Entomol. 113: 18501857.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Price, T., Valverde, R., Singh, R., Davis, J. A., Brown, S. and Jones, H., 2020. First report of cotton Leafroll dwarf virus in Louisiana. Plant Health Progress, https://doi.org/10.1094/PHP-03-20-0019-BR.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Souza, M. F., and Davis, J.A. 2020. Detailed characterization of Melanaphis sacchari (Hemiptera: Aphididae) feeding behavior on different host plants. Environ. Entomol. 49: 683-691.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Souza, M. F., and Davis, J.A. 2020. Potential population growth of Melanaphis sacchari (Zehntner)(Hemiptera: Aphididae) under six constant temperatures on grain sorghum (Sorghum bicolor L.). Florida Entomol. 103: 116-123.

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:Producers, consultants, extension agents and researchers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project is providing professional development of two PhD students. How have the results been disseminated to communities of interest?Results have been disseminated through talks at professional meetings and through 1 peer reviewed journal article. What do you plan to do during the next reporting period to accomplish the goals?This project has only been active for one year prior to reporting on progress. We will continue to work on the objectives listed above, addressing changes as needed.

Impacts
What was accomplished under these goals? First, field movement of aphids was examined to identify trends in vector abundance throughout the sweetpotato growing season. Aphid abundance at the sites sampled appears to reflect the population dynamics of the most commonly collected species, the non-vector Melanaphis sacchari. Sweetpotato virus vectors numbers were consistently low throughout the years sampled, and there were no discernable trends in vector abundance, which suggest that aphid control tactics should be deployed early in the season when sweetpotato is most vulnerable to virus transmission. Headspace volatiles of sweetpotato were collected to determine if virus infection status had an effect on the sweetpotato volatile profile. Thirteen compounds were produced by virus tested sweetpotato and 21 compounds were produced by infected sweetpotato. Compounds induced by virus infection were mainly green leaf volatiles and terpenes, many of which affect insect behavior. Additionally, this was the first recorded effort to identify volatiles from sweetpotato free of known diseases. Green peach aphid (GPA) preferred the odor of infected plants over virus tested plants, and the odor of virus tested plants and MESA over the odor of virus tested plants alone. GPA preferred the odor of virus tested plants alone over that of plant and MEJA or plant and neem oil. Settling assays were performed to determine if these preferences had any effect on aphid settling behavior. While GPA preferred plants treated with MESA, contrary to the result of the Y-tube assays, aphids preferred to settle on virus infected plants and neem oil treated plants over virus tested plants. This suggests that orientation towards odors does not necessarily indicate settling preference in GPA. The effect of headspace volatiles on aphid feeding on infected and virus tested sweetpotato was examined in order to determine if volatile treatments that do not directly affect the plant affect aphid feeding behavior. Both GPA and cotton aphid exhibited changes in behaviors related to virus transmission in the presence of all volatile treatments compared to controls when feeding on both virus tested and virus infected plants, suggesting that exposure to headspace volatiles while feeding affects aphid feeding behavior. However, in virus transmission assays, exposure to these volatiles during feeding did not affect the number of plants showing virus symptoms, suggesting that the changes in behavior are too subtle to affect transmission rates. We found that transmission of SrMV differs among two aphid species; M. sacchari and M. persicae. M. sacchari failed to transmit SrMV both singly and in groups under laboratory conditions. Based on our results, we state that M. sacchari is a non-vector of SrMV in sorghum. M. persicae, however, successfully transmitted SrMV in sorghum in our studies at different efficiencies (4.2 to 8.2 %), depending upon whether they were allowed to transmit singly or in groups. Studies of feeding behavior by EPG suggested that by virtue of producing higher numbers of probes during feeding, a longer potential drop duration with longer subphases II-1 and II-3, higher number of archlets during subphase II-3, and quicker to produce first potential drops than M. sacchari, M. persicae possesses an ability to successfully transmit SrMV from sorghum to sorghum. We conducted greenhouse and laboratory experiments to determine the effects of Cucumber mosaic virus or Sunn-hemp mosaic virus infected cowpea on soybean looper and fall armyworm larval growth and adult oviposition preference. We found that both viruses didn't affect soybean looper larval growth. However, fall armyworm larvae benefitted upon feeding on CMV-infected cowpea leaves in our studies.In the oviposition preference study, we observed that soybean looper and fall armyworm adults preferred to lay more eggs on the healthy plants as compared to the virus-infected ones. Based on our results, we propose that plant viruses may be "benefitting" themselves from non-vector herbivores by discouraging adult oviposition and subsequent larval feeding on the infected hosts in order to ensure their movement and spread by vector herbivores. We conducted lab experiments to understand if BPEV-infection provides any benefit to bell pepper hosts against a common pest, M. persicae. We designed experiments to determine preference behavior, host suitability and population dynamics of M. persicae on BPEV-infected and non-infected pepper plants. Through host preference bioassays, we found that M. persicae preferred virus-free leaves as compared to virus infected ones. This could indicate that BPEV infection might have benefitted the host by making them unattractive to the vector herbivores and could be reducing virus inoculation of non-persistent viruses. Moreover, we also found that BPEV negatively affected longevity and fecundity of aphids. The findings of this study provide an important first step towards understanding the complex interaction that occur between BPEV, bell pepper and M. persicae.

Publications

• Type: Theses/Dissertations Status: Published Year Published: 2019 Citation: EFFECTS OF PLANT VIRUSES ON VECTORS AND NON-VECTOR HERBIVORES IN THREE DIFFERENT PATHOSYSTEMS by S. Paudel, PhD Dis.
• Type: Theses/Dissertations Status: Published Year Published: 2019 Citation: EFFECTS OF VIRUS INFECTION AND VOLATILES ON APHID VIRUS VECTOR BEHAVIOR ON SWEETPOATO by J. Dryburgh, PhD Dis.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Li, Z., J. A. Davis, and D. R. Swale. 2019. Chemical inhibition of Kir channels reduces salivary secretions and phloem feeding of the cotton aphid, Aphis gossypii (Glover). Pest Manag. Sci. doi: 10.1002/ps.5382.

Progress 09/06/18 to 09/30/18

Outputs
Target Audience:Producers, consultants, extension agents and researchers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project is providing professional development of two PhD students. How have the results been disseminated to communities of interest?Results have been disseminated through talks at professional meetings. What do you plan to do during the next reporting period to accomplish the goals?This project has only been active for one month prior to reporting on progress. We have just initiated the objectives listed above and will continue to work on those, addressing changes as needed.

Impacts
What was accomplished under these goals? We evaluated the impacts of plant viruseson feeding, growth, and oviposition preference of soybean looper, Chrysodeixis includens (Walker) and fall armyworm, Spodoptera frugiperda (JE Smith), in soybean, Glycine max (L.), and cowpea, Vigna unguiculata (L.) ,infected with Cucumber mosaic virus (Cucumovirus, Bromoviridae) or Sunn-hemp mosaic virus (Tobamovirus, Virgaviridae). Soybean looper larvae showed no differences in body weight and defoliation on virus infected and non-infected leaves. However, fall armyworm showed significant differences in 7-day weight gain on cowpea when infected with either virus. Oviposition choice assays showed a statistically significant preference for virus-free plants. Based on our results, we propose that plant viruses may be "protecting" themselves from other herbivores in order to ensure their movement and spread by a vector herbivore. However, even though adults preferentially choose to oviposit on healthy plants, fall armyworm larvae seem to benefit from feeding on virus-infected cowpea leaves.

Publications