Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Weekly during the growing season in 12 alfalfa fields in Kent County, Delaware populations of alfalfa weevil larvae and adults, potato leafhoppers, pea aphids, leaf blotch miners and tarnished plant bug nymphs and adults were monitored. Throughout the growing season outbreaks of alfalfa weevils, potato leafhoppers, pea aphids and tarnished plant bugs did occur and exceeded the economic threshold. Because of successful USDA-ARS classical biological control projects, insect pest control for alfalfe has been biologically based. However, about 70 percent of the alfalfa growers still relied on spraying for control. All tarnished plant bug (Lygus lineolaris) nymphs were sent to the USDA-ARS Beneficial Insect Introduction Lab and reared to adults to determine degree of paratism. Three indigenous parasitoid species, Leiophron uniformis, Peristenus pallipes and P. pseudopallipes, were recovered from tarnished plant bug nymphs, but levels of parasitization were extremely low, less than 1 percent on average. The tarnished plant bug, not only feeds on alfalfa but it is a pest of over half of the 30 most important crops in the U. S. It has been brought under control in most areas north of 40.5 degree N latitude (corresponding to New York City) by Peristenus digoneutis, a nymphal parasite of European origin established by USDA-ARS scientists in the 1980s. Unfortunately, this species has not spread south of New Youk City, so more southern populations of tarnished plant bug have not been impacted by this parastoid. During the 2006, 2007 alfalfa growing seasons and again in 2008 25,000 P. relicuts (tarnished plant bug parastitoids) were obtained from the State of New Jersey, Dept. of Agri. and released weekly into four alfalfa fields in Delaware that are part of the weekly sampling program. P. relicuts is the dominate parasite of lygus bugs in southern Europe. The first P. relicuts, a female, was recovered on July 25, 2007 from a caged adult release. In addition, on the same date, a P. digoneutis was recovered, a new county recovery. So far in 2008 three more P. relicuts have been recovered. A second objective was to establish economic thresholds for potato leafhopper in resistant (glandular-haired) cultivars of alfalfa. Five glandular-haired and two susceptible cultivars were established. To achieve different levels of pest pressure in 2006 and 2007 leafhopper densities of 0, 40, 80 and 160 per cage were covered over an area of 0.21 m/sq for 30 days. The economic threshold for the two susceptible varieties when averaged over 168 observations (2 varieties x 4 reps x 3 potato leafhopper densities x 4 harvest at one location and x 3 harvest at another location) was found to be 2.8 per 10 sweeps, which is consistant with current recommendations. The economic threshold for the resistant varieties when averaged over 420 observations (5 varieties x 4 reps x 3 potato leafhopper densities x 4 harvests at one location and x 3 harvests at another location) was found to be 4.9 per 10 sweeps. Therefore, a farmer using resistant alfalfa varieties will not need to use control measures to control potato leafhoppers in alfalfa until the count per 10 sweeps is 5 or greater. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Communities and Consumers. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
If the tarnished plant bug can be brought under control in areas south of 40.5 degree N latitude by establishing Peristenus relicuts, the dominate parasite of lygus bugs in southern Europe for release in alfalfa fields in Delaware, it has the potential of saving food and fiber producers an estimated 350 million dollars annually, similar to money being saved with controlling alfalfa weevil biologically. Although the leafhopper can be controlled with insecticides, recent development of resistant varieties demonstrated a large reduction in the use of pesticides needed to control this pest. The newer alfalfa varieties resistant to potato leafhopper demonstrated a 43 percent greater resistant when compared to the susceptible varieties. Thus, if alfalfa growers seed the new glandular-haired alfalfa varieties resistant to potato leafhopper, they will not need to spray until the count per 10 sweeps in 5 or greater; thus, using less insecticide and reducing production costs.
Publications
- Gibson, Lindsey N. 2008. Economic Thresholds for Potato Leafhopper (Empoasca fabae)(Harris)) on Glandular-Haired Varieties of Alfalfa (Medicago sativa L.). M. S. Thesis. Delaware State University, Dover, DE
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Progress 01/01/07 to 12/31/07
Outputs
Weekly during the growing season in 12 alfalfa fields in Kent County, Delaware the number of alfalfa weevil larvae and adults, number of potato leaf hoppers, number of pea aphids, number of leaf blotch miners, and number of tarnished plant bug nymphs and adults were monitored. Throughout the growing season outbreaks of alfalfa weevils, potato leafhoppers, pea aphids and tarnish plant bugs did occur and exceeded the economic threshold. Because of successful USDA-ARS classical biological control projects, insect pest control for alfalfa has been biologically-based. However, about 70 percent of the alfalfa growers still relied on spraying for control. All tarnished plant bug (Lygus lineolaris) nymphs were taken to the USDA-ARS Beneficial Insect Introduction Research Lab and reared to adults to determine degree of parasitism. Three indigenous parasitoid species, Leiophron uniformis, Peristenus pallipes and Peristenus pseudopallipes, were recovered from tarnished plant bug
nymphs, but levels of parasitization were extremely low, less than 1 percent on average. The tarnished plant bug, not only feeds on alfalfa but it is a pest of over half of the 30 most important crops in the U. S. It has been brought under control in most areas north on 40.5 degree N latitude (corresponding to New York City) by Peristenus digoneutis, a nymphal parasite of European origin established by USDA-ARS scientists in the 1980s. Unfortunately, this species has not spread south of New York City, so more southern populations of tarnished plant bug have not been impacted by this parasitoid. During the 2006 alfalfa growing season and again in 2007 25,000 Peristenus relicuts (tarnished plant bug parastitoids) were obtained from the State of New Jersey, Department of Agriculture and released weekly into four alfalfa fields in Delaware that are part of the weekly sampling program. P. relicuts is the dominant parasite of lygus bugs in southern Europe. The first P. relictus, a female,
was recovered on July 25, 2007 from a caged adult release. In addition, on the same date, a P. digoneutis was recovered, a new county recovery. A second objective was to establish economic thresholds for potato leafhopper in resistant (Glandular-haired) cultivars of alfalfa. Five glandular-haired and two susceptible cultivars were established. The glandular-haired cultivars were: WL-346LH, Mycogen 4375LH, DKA-3720, Trailblazer 4.0 and PEGASUS. Susceptible controls were Saranac AR and Cimarron. To achieve different levels of pest pressure in 2006 and 2007 potato leafhopper densities of 0, 40, 80 and 160 per cage were caged over an area of 0.21 m/sq and randomly assigned with all four densities in each plot for 30 days. At potato leafhopper infestations of 40, 80 and 160, susceptible cultivars showed yellowing of the foliage, reduced yield, quality and dead plants. All glandular-haired cultivars demonstrated high resistance to potato leafhopper at both 80 and 160 levels of infestations
and difference among cultivars. A graduate student has collected two year of data and will graduate May 2008 and earn a Master of Science degree in Plant Science from Delaware State University.
Impacts
If the tarnished plant bug can be brought under control in areas south of 40.5 degree N latitude by establishing Peristenus relictus, the dominant parasite of lygus bugs in southern Europe for release in alfalfa fields in Delaware, it has the potential of saving food and fiber producers an estimated 350 million dollars annually, similar to money being saved with controlling the alfalfa weevil biologically. Although the leafhopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the use of pesticides needed to control this pest, but separate economic thresholds for these varieties are needed. Thus, the establishment of economic thresholds for potato leafhopper in resistant (glandular-haired) varieties of alfalfa will result in using less insecticides and lower production costs.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
The project was a joint effort with the UDSA ARS Beneficial Insects Introduction Research Lab (BIIRL), Newark, Delaware. To assess the over abundance of and damage by alfalfa insect pests in Delaware, weekly throughout the growing season 12 alfalfa fields in Kent County Delaware were sampled for alfalfa weevil, potato leafhopper, pea aphid, tarnished plant bug, alfalfa plant bug and alfalfa blotch leafminer. The abundance of potato leafhopper was strongly (P<0.0001) and positively correlated with the abundance of tarnished plant bug (r=0.619), alfalfa plant bug (r=0.378), height of alfalfa (r=0.345), and the previous week's leafhopper counts (r=0.547). Hopper burn was strongly (P=<0.0001) and positively correlated with leafhopper counts on the same (r=0.331) and previous week's (r=0.364) sampling date, the abundance of tarnished plant bugs (r=0.362) and alfalfa (r=0.332) plant bugs, and height of alfalfa (r=0.252). Populations of alfalfa weevil peaked between April 23
and May 13 and 50% of the alfalfa growers sprayed an insecticide. The abundance of alfalfa larvae was strongly (P=0.001) and positively correlated with larvae counts the previous week (r=0.402), adult counts on the date sampled (r=0.381), and plant height in cm (r=0.291). A second objective was to establish economic thresholds for potato leafhopper in resistant (Glandular-haired) cultivars of alfalfa. Five glandular-haired and two susceptible cultivars were established and all seven cultivars showed no complete resistant to potato leafhopper. However, the resistant cultivars possessed a greater yield potential then susceptible cultivars under potato leafhopper conditions. A third objective was an attempt to establish Peristenus stygicus to control populations of tarnished plant bug (Lygus lineolaris), in alfalfa fields in Delaware. During 2006 weekly releases were made from June 26 through September 25 of 10,000 Peristenus stygicus adults in each of two alfalfa fields and 10,000
Peristenus stygicus parasitized nymphs in each of two alfalfa fields. In addition, two methods of releases were compared: live adults vs. lab-parasitized nymphs. All tarnished plant bug nymphs were taken to the USDA ARS BIIRL and reared to adults to determine degree of parasitism. Throughout the growing season no alfalfa grower sprayed specifically for the tarnished plant bug, but they were sprayed when other pest were being sprayed. Three indigenous parasitoid species, Leiophron uniformis, Peristenus pallipes and Peristenus pseudopallipes, were recovered from tarnished plant bug nymphs, but levels of parasitization were extremely low, less than 1% on average. One male Peristenus stygicus may have been recovered from a tarnished plant bug nymph. The good news is currently being verified. In 2007 we will attempt recovery thereof, and document establishment.
Impacts
The tarnished plant bug (Lygus lineolaris), not only feeds on alfalfa but it is a pest of over half of the 30 most important crops in the U. S., that it has a major impact on the agroecosystem. The insect is highly mobile, and can move from one crop to another very quickly. It has been brought under control in most areas north of 40.5 degree N latitude (corresponding to New York City) by Peristenus digoneutis in the 1980's. But south of New York City populations of tarnished plant bug have not been impacted by this parasitoid. If the tarnished plant bug can be brought under control in areas south of 40.0 degree N latitude by establishing Peristenus stygicus, the most important parasitoid of lygus bugs in the southern regions of Europe, farmers in Delaware growing alfalfa and other susceptible crops could save an estimated 5 million dollars annually. In addition, food and fiber producers in the southern states could save an estimated 300 million dollars by having
Peristenus stygicus moving into their crop fields and controlling the tarnished plant bug. Although the leafhopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the use of pesticides needed to control this pest, but separate economic threasholds for these new varieties are needed. Thus, the establishment of economic threasholds for potato leafhopper in resistant (glandular-haired) varieties of alfalfa will result in using less inasecticides and lower production costs.
Publications
- No publications reported this period
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