Title: Pheromonal divergence between two strains of Spodoptera frugiperda Authors
|Unbehend, Melanie -|
|Hanniger, Sabine -|
|Heckel, David -|
|Groot, Astrid -|
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2013
Publication Date: March 1, 2013
Citation: Unbehend, M., Hanniger, S., Meagher Jr, R.L., Heckel, D.G., Groot, A.T. 2013. Pheromonal divergence between two strains of Spodoptera frugiperda. Journal of Chemical Ecology. 39(3):364-376. Interpretive Summary: Fall armyworm is a moth pest that attacks many agricultural crops such as corn, sorghum, pasture and turf grasses, rice, cotton, peanuts, and sugarcane. The species is composed of two types or host strains, one that feed mostly on large grasses and cotton (corn strain) and one that feeds on small grasses (rice strain). However, both host strains can be in the same area and can attack the same crops at the same time. Since the host strains can hybridize, researchers have tried to determine how the two host strains keep their individual characteristics. One possible method is for the females to release different pheromone blends that attract only males of their own host strain. Scientists at the Max Planck Institute for Chemical Ecology in Jena, Germany, and scientists at the USDA/Agriculture Research Service, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, tested different pheromone blends in different habitats in Florida and then determined the host strain of the males that were collected. Results suggested that males are attracted to blends from both host strain females and that the small differences in pheromone blends between the host strains are not enough to keep them from intermating.
Technical Abstract: Abstract- Spodoptera frugiperda consists of two genetically and behaviorally different strains, the corn- and the rice-strain, which seem to be in the process of sympatric speciation. We investigated the role of strain-specific sexual communication as a prezygotic mating barrier between both strains by analyzing strain-specific variation in a) female pheromone composition of laboratory and field strains, and b) male attraction in wind tunnel and field experiments. Laboratory and field females from Florida exhibited strain-specific differences in their relative amount of (Z)-7-dodecenyl acetate (Z7-12:OAc) and (Z)-9-dodecenyl acetate (Z9-12:OAc). In wind tunnel assays, we did not find strain-specific attraction of males to females. However, in field experiments in Florida, we observed some differential attraction to synthetic pheromone blends. In a corn field, the corn-strain blend attracted more males of both strains than the rice-strain blend, but both blends were equally attractive in a grass field. Thus, habitat-specific volatiles seemed to influence male attraction to pheromones. In dose-response experiments, corn-strain males were more attracted to 2% Z7-12:OAc than other doses tested, while rice-strain males were attracted to a broader range of Z7-12:OAc (2-10 %). The attraction of corn-strain males to the lowest dose of Z7-12:OAc corresponds to the female production, as corn-strain females produced significantly smaller amounts of Z7-12:OAc than rice-strain females. Although corn-strain individuals are more restricted in their production of and response to pheromones than rice-strain individuals, it seems that the sexual communication differences between corn- and rice-strain individuals are not strong enough to cause assortative mating.