|Lopez, Juan De Dios|
Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2007
Publication Date: 12/1/2007
Citation: Blanco, C.A., Teran-Vargas, A.P., Lopez, J., Kauffman, J.V. 2007. Naturally-occurring densities of Heliothis virescens and Helicoverpa zea (Lepidoptera: noctuidae) in three different plant hosts. Florida Entomologist. 90:742-750. Interpretive Summary: In 1996, Dr. Fred Gould (North Carolina State University) and a group of collaborators found out that one in every 1,000 tobacco budworms present in the field had a Bacillus thuringiensis (Bt) Cry1Ac toxin resistant gene. Cry1Ac is the insecticide expressed in transgenic cotton (Bt-cotton) that provides control of this insect. Monitoring the resistance levels to Bt proteins is an annual requirement that EPA demands from Bt-cotton registrants. The USDA, ARS in Stoneville, Mississippi serves as the institution that tests tobacco budworm (and bollworm) susceptibility to Bt. Since resistant individuals are so rare in the population, ideally a test should include at least 1,000 different tobacco budworms in order to have the likelihood of detecting a resistant one. Tests evaluating so many insects are usually constrained by the availability of such large numbers of tobacco budworms at any given time. This 3-year, 2-location (Mississippi and Tamaulipas, Mexico) study evaluated the potential of 3 plant species, cotton, garbanzo bean and velvetleaf, to produce large numbers of tobacco budworms (main objective) and bollworms. Garbanzo beans produced 14 and 5 times more tobacco budworm larvae than cotton or velvetleaf respectively. Bollworm larvae were also 40 and 2 times more abundant on garbanzo bean than on cotton or velvetleaf. This information serves as a reliable indicator that plots seeded with garbanzo bean can provide the necessary tobacco budworms to conduct reliable Bt monitoring tests. This technique has already been adopted in Texas, Alabama, Georgia and Arkansas, Florida, Mexico and Mississippi in 2005 by collaborators of the Bt resistance monitoring program.
Technical Abstract: Large numbers of field-collected tobacco budworms Heliothis virescens L., and/or bollworms Helicoverpa zea (Boddie) (heliothines) might be difficult to obtain from certain crops, geographies and at a given moment in time to perform laboratory tests. Of the >95 cultivated and wild plants that have been identified as hosts, some are highly attractive and can be used to collect both insect species, however, the reliability of these plants in space and time in providing large numbers of these insects is not well understood. Quantifying naturally-occurring densities of heliothines throughout the entire life cycle of a host plant can assist in getting this information. We studied heliothine populations over a three-year period in two different geographic locations in plots of garbanzo bean Cicer arietinum L, upland cotton Gossipium hirsutum L., and velvetleaf Abutilon theophrasti Medikus. Garbanzo bean produced up to 14- and 5-fold significantly higher numbers of tobacco budworm larvae as compared to cotton and velvetleaf respectively. Bollworm larvae had 40- and 2-fold higher numbers on garbanzo bean than in the other two plant species, although not consistent in all years. Presence of larvae on garbanzo bean coincided more with cotton than with velvetleaf. Tobacco budworm and bollworm moths also emerged in higher quantities from garbanzo bean than from cotton or velvetleaf, coinciding with the emergence of lower numbers of moths after development on the other two plants species. For obtaining large numbers of both insect species for a diversity of field and laboratory studies, garbanzo bean, due to its high larval and moth production and its adaptation for growing at colder temperatures not suitable for the other plant species, offer a clear advantage over cotton or velvetleaf to improve the collection of feral heliothines. KEY WORDS: Tobacco budworm, bollworm, Cicer arietinum, Gossipium hirsutum, Abutilon theophrasti, larval and moth densities.