|Throne, James - Jim|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/19/2005
Publication Date: 2/20/2006
Citation: Qureshi, J.A., Buschman, L.L., Throne, J.E., Ramaswamy, S.B. 2006. Dispersal of adult Diatraea grandiosella (Lepidoptera: Crambidae) and its implications for corn borer resistance management in Bacillus thuringiensis maize. Annals of the Entomological Society of America 99: 279-291. Interpretive Summary: The southwestern corn borer is a destructive pest of corn in the southern parts of North America, where the annual cost of control and damage is in the millions of dollars. Southwestern corn borer is a primary target of transgenic Bt corn hybrids; however, there is concern that the southwestern corn borer could develop resistance to the insecticidal protein expressed in Bt corn plants. Insecticide-resistance management strategies have been developed to try to slow resistance to the insecticidal protein, but, for these strategies to work, there needs to be enough dispersal of adults between transgenic and nontransgenic “refuge” crop fields to allow genetic mixing of the populations to suppress development of pest resistance to the transgenic crop. Dispersal of southwestern corn borer adults was investigated in western Kansas where corn is grown under irrigation in a semi-arid climate to determine whether dispersal assumptions used in development of the resistance management strategy for European corn borer could also be applied to southwestern corn borer. Dispersal of marked insects was similar to that for European corn borer and suggests that a minimum distance of 350 m between Bt corn and non-Bt corn “refuge” would be appropriate; however, dispersal of naturally occurring adults suggests that dispersal from neighborhood fields was more extensive than suggested by marked adults. However, it is not clear if the dispersal recorded in this study is extensive enough to support the current resistance management strategy for corn borers.
Technical Abstract: Dispersal of the southwestern corn borer, Diatraea grandiosella Dyar, was examined by release and recapture of dye-marked adults and by capture of feral adults in and around 50 ha center pivot irrigated fields of Bacillus thuringiensis (Bt) maize. Pheromone and black light traps were used to capture the adults. In 1999, 2000, and 2001, a total of 177, 602, and 1,292 marked males, and 87, 231, and 1,045 marked females were released in four irrigated Bt-maize fields, respectively. Recapture beyond release point was 2.13, 6.17, 3.16, and 17.91% for males and 0, 0, 2.23, and 4.18% for females in the four fields, respectively. One male was recaptured over native vegetation outside the field perimeter, and one was caught in a neighboring maize field, 457 m from the release point. An exponential decay function explained recapture of marked adults across the dispersal distance. More than 90% of adults were recaptured within 300 m of the release point. Large numbers of feral adults were captured throughout the study fields and over native vegetation between fields. The feral adult dispersal could be described with a linear model. Virgin females (38% marked and 14% feral) were captured throughout the study fields. The recapture of marked insects suggests that the dispersal was limited. However, capture of feral adults throughout Bt-maize fields indicates that the actual dispersal may be more extensive than indicated by recapture of marked adults. Potential refuge sources for the feral adults were 587 to 1387 m from the edge of the fields. There appears to be some dispersal of corn borers from the nontransgenic “refuge” fields into the transgenic fields that allows some genetic mixing of the two populations. Such genetic mixing may help suppress potential development of pest resistance to transgenic maize. However, it is not clear if the dispersal recorded in this study is extensive enough to support the current resistance management strategy for corn borers.