Migration-Related Insect Problems Encountered in Nebraska in 1997 Gary L. Hein, State Representative Panhandle Research and Extension Center Scottsbluff, Nebraska The most serious migratory insect problem in Nebraska for 1997 was the potato leafhopper. This insect will establish in some years in eastern Nebraska and cause problems in alfalfa and potatoes. However, it has not been known to migrate into the Nebraska panhandle early enough and in numbers great enough to ever cause problems. This year the potato leafhopper was found in economic infestations in the panhandle in late June in alfalfa, potatoes, and dry beans. Serious infestations continued through the summer throughout all of Nebraska. Based on the size of the nymphs found in late June on alfalfa, we estimate that the leafhopper arrived in the panhandle about June 5-10. Strong southerly wind flows occurred at this time for several days. Another insect that does not overwinter in Nebraska, but migrates in each year is the sunflower head moth. Head moth populations this year were very much greater than we have seen for the last several years. Pheromone trap catches in the earliest planted sunflower fields that began heading about August 5 indicated severe infestations of the head moth. This insect migrates likely from the southerly regions of the Great Plains. Therefore, migration does not occur from as distant a region as the potato leafhopper. Two additional migratory insects caused problems in Nebraska in 1997. The army cutworm, which migrates from the Rocky mountains in the fall to lay their eggs, caused problems in southwest Nebraska alfalfa fields in the spring. The sugarbeet root aphid, which migrates from the Rocky mountains in the early summer, established widespread infestations in western Nebraska sugarbeet fields. Movement of the Wheat Curl Mite and Its Impact on the Epidemiology of Wheat Streak Mosaic and High Plains Viruses The wheat curl mite is an Eriophyid mite of considerable importance to wheat on the Great Plains. This mite transmits two viruses that cause disease in winter wheat throughout the Great Plains and the Pacific Northwest. These are the most important disease problems in the western Great Plains. Management of the disease relies on the ability to manage mite populations during the over summering period between wheat maturity in the summer and the emergence of the new crop of winter wheat in the fall. The most important of these over summering hosts is volunteer wheat that has resulted from hail storms that have shelled out and germinated the wheat before harvest thus providing a summer green bridge for the mites. The management of this mite is complicated by its ability to move, and the study of the movement of this mite is complicated by the size of the mite. This mite is extremely small (ca. 150-250 microns in length) as are all Eriophyids. The study of these mites requires a great deal of labor for counting or the development of special techniques that allow the adequate sampling of the mite either from their host plants or from the air as they are moving. We are trying to develop techniques that allow us to better monitor these mites in the field so that we can continue and expand our study of the ecology of this mite. Wheat curl mite survival off the plant: Studies have been conducted to determine the length of time the mites can survive off the plant. Historical evidence indicates that survival of the mites would be very short off the plant. Therefore, movement of the mite has been assumed to be of only a very short distance. Mites were held at different temperatures in isolation chambers and the survival of the mites monitored over time. At temperatures above 20 degrees C mites survived less than 12 hours, but as temperatures were reduced the mites survived considerably longer with the some mites surviving to five days at 5 degrees C. It was also noted that the mites survived longer at higher humidity. We are in the process of further delineating mite survival under various temperature and humidity regimes. We also will be determining their ability to reestablish and subsequently transmit the viruses after a period off the plants. This preliminary work indicates that the mites may have the potential for moving longer distances than just local field to field movement. Impact of post-harvest volunteer on fall infestations: Over the last four years we have been examining the potential for post harvest volunteer to serve as sites of over summering buildup of mite populations. Monitoring of volunteer that has emerged after harvest has indicated that the threat of disease infections is substantially limited in post harvest volunteer. We have also been investigating the impact of wheat variety of the volunteer and have shown that volunteer resulting from curl mite resistant varieties will have even more reduced potential for creating a significant disease situation. Factors that trigger mite movement off of plants and subsequent disease spread: We are beginning to investigate the reasons that trigger mite movement off of the plants. Field trials have been done that indicate that Roundup, when applied to volunteer near or after winter wheat planting time, acts to increase the potential for viral infections in neighboring wheat. Future studies are planned to determine the major trigger mechanisms that influence when mites are likely to move. Related Publications: McNeil, J. E., R. French, G. L. Hein, P. S. Baenziger, and K. M. Eskridge. 1996. Characterization of genetic variability among natural populations of wheat streak mosaic virus. Phytopathology 86:1222-1227. Mahmood, T., G. L. Hein, and R. C. French. 1997. Development of serological procedures for rapid and reliable detection of wheat streak mosaic virus in a single wheat curl mite. Plant Dis. 81:250-253. Mahmood, T., G. L. Hein, and S. G. Jensen. 1997. Mixed infection of wheat with high plains virus and wheat streak mosaic virus from wheat curl mites in Nebraska. Plant Dis. (in press) Hein, G. L. 1997. Wheat Curl Mite. In: ESA Handbook of Corn Insects. Entomological Society of America (in press) [ 1997 Research Index ]
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Migration-Related Insect Problems

Encountered in Nebraska in 1997

Gary L. Hein, State Representative
Panhandle Research and Extension Center
Scottsbluff, Nebraska

The most serious migratory insect problem in Nebraska for 1997 was the potato leafhopper. This insect will establish in some years in eastern Nebraska and cause problems in alfalfa and potatoes. However, it has not been known to migrate into the Nebraska panhandle early enough and in numbers great enough to ever cause problems. This year the potato leafhopper was found in economic infestations in the panhandle in late June in alfalfa, potatoes, and dry beans. Serious infestations continued through the summer throughout all of Nebraska. Based on the size of the nymphs found in late June on alfalfa, we estimate that the leafhopper arrived in the panhandle about June 5-10. Strong southerly wind flows occurred at this time for several days.

Another insect that does not overwinter in Nebraska, but migrates in each year is the sunflower head moth. Head moth populations this year were very much greater than we have seen for the last several years. Pheromone trap catches in the earliest planted sunflower fields that began heading about August 5 indicated severe infestations of the head moth. This insect migrates likely from the southerly regions of the Great Plains. Therefore, migration does not occur from as distant a region as the potato leafhopper.

Two additional migratory insects caused problems in Nebraska in 1997. The army cutworm, which migrates from the Rocky mountains in the fall to lay their eggs, caused problems in southwest Nebraska alfalfa fields in the spring. The sugarbeet root aphid, which migrates from the Rocky mountains in the early summer, established widespread infestations in western Nebraska sugarbeet fields.

Movement of the Wheat Curl Mite and Its Impact on the Epidemiology of Wheat Streak Mosaic and High Plains Viruses

The wheat curl mite is an Eriophyid mite of considerable importance to wheat on the Great Plains. This mite transmits two viruses that cause disease in winter wheat throughout the Great Plains and the Pacific Northwest. These are the most important disease problems in the western Great Plains. Management of the disease relies on the ability to manage mite populations during the over summering period between wheat maturity in the summer and the emergence of the new crop of winter wheat in the fall. The most important of these over summering hosts is volunteer wheat that has resulted from hail storms that have shelled out and germinated the wheat before harvest thus providing a summer green bridge for the mites. The management of this mite is complicated by its ability to move, and the study of the movement of this mite is complicated by the size of the mite. This mite is extremely small (ca. 150-250 microns in length) as are all Eriophyids. The study of these mites requires a great deal of labor for counting or the development of special techniques that allow the adequate sampling of the mite either from their host plants or from the air as they are moving. We are trying to develop techniques that allow us to better monitor these mites in the field so that we can continue and expand our study of the ecology of this mite.

Wheat curl mite survival off the plant: Studies have been conducted to determine the length of time the mites can survive off the plant. Historical evidence indicates that survival of the mites would be very short off the plant. Therefore, movement of the mite has been assumed to be of only a very short distance. Mites were held at different temperatures in isolation chambers and the survival of the mites monitored over time. At temperatures above 20 degrees C mites survived less than 12 hours, but as temperatures were reduced the mites survived considerably longer with the some mites surviving to five days at 5 degrees C. It was also noted that the mites survived longer at higher humidity. We are in the process of further delineating mite survival under various temperature and humidity regimes. We also will be determining their ability to reestablish and subsequently transmit the viruses after a period off the plants. This preliminary work indicates that the mites may have the potential for moving longer distances than just local field to field movement.

Impact of post-harvest volunteer on fall infestations: Over the last four years we have been examining the potential for post harvest volunteer to serve as sites of over summering buildup of mite populations. Monitoring of volunteer that has emerged after harvest has indicated that the threat of disease infections is substantially limited in post harvest volunteer. We have also been investigating the impact of wheat variety of the volunteer and have shown that volunteer resulting from curl mite resistant varieties will have even more reduced potential for creating a significant disease situation.

Factors that trigger mite movement off of plants and subsequent disease spread: We are beginning to investigate the reasons that trigger mite movement off of the plants. Field trials have been done that indicate that Roundup, when applied to volunteer near or after winter wheat planting time, acts to increase the potential for viral infections in neighboring wheat. Future studies are planned to determine the major trigger mechanisms that influence when mites are likely to move.

Related Publications:

McNeil, J. E., R. French, G. L. Hein, P. S. Baenziger, and K. M. Eskridge. 1996. Characterization of genetic variability among natural populations of wheat streak mosaic virus. Phytopathology 86:1222-1227.

Mahmood, T., G. L. Hein, and R. C. French. 1997. Development of serological procedures for rapid and reliable detection of wheat streak mosaic virus in a single wheat curl mite. Plant Dis. 81:250-253.

Mahmood, T., G. L. Hein, and S. G. Jensen. 1997. Mixed infection of wheat with high plains virus and wheat streak mosaic virus from wheat curl mites in Nebraska. Plant Dis. (in press) Hein, G. L. 1997. Wheat Curl Mite. In: ESA Handbook of Corn Insects. Entomological Society of America (in press)

[ 1997 Research Index ]