Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2003
Publication Date: 4/15/2004
Citation: Peterson, R.K.D., C.L. Shannon, and A.W. Lenssen. 2004. Photosynthetic responses of legume species to actual and simulated insect defoliation. Environmental Entomol. 33:450-456. Interpretive Summary: Relatively few plant species have been examined for plant physiological changes due to insect herbivory. It is unknown whether responses to leaf-mass removal by insects vary among plant families and species. The goal of this research was to determine if gas exchange and photosynthesis vary among cultivated legumes subjected to simulated or actual leaf-mass consumption by fall armyworm. Our results support the idea that there is a generalized plant gas exchange response to leaf-mass consumption injury among the cultivated legumes, and that this generalized plant response may extend to many plant species.
Technical Abstract: Several studies have addressed plant primary physiological responses (gas exchange responses) to insect herbivory. However, relatively few plant species have been examined. It is unknown whether responses to leaf-mass removal by insects vary among plant families and species. Within the legumes, only alfalfa, Medicago sativa L., and soybean, Glycine max (L.) Merrill, have been examined. The goal of this study was to test the hypothesis that gas exchange responses to leaf-mass consumption in a broad range of cultivated legumes do not differ from those of soybean and alfalfa. The species and cultivars used were M. sativa Cimarron, Medicago scutellata (L.) Sava, Medicago truncatula Gaertner Paraggio, Melilotus officinalis (L.) Pallas, Trifolium hybridum L., and Trifolium pratense L. Twelve greenhouse experiments were conducted and each legume species was used in a separate experiment. Depending on the experiment, there were either two or three treatments (control, simulated insect injury, and actual insect injury). For simulated and actual insect defoliation, injury was limited to a single leaf per plant. Simulated insect injury treatments were imposed by removing leaf tissue on each leaflet with scissors. For the actual insect defoliation treatment, fall armyworm larvae, Spodoptera frugiperda (J.E. Smith), were used. Defoliation of single leaves on the six species resulted in similar responses. Plant gas exchange variables (Photosynthesis, stomatal conductance, intercellular CO2, and transpiration) were not significantly affected by either simulated or actual insect defoliation. Our results support the hypothesis that there is a generalized primary physiological response to leaf-mass consumption injury among the cultivated legumes. More generally, the results from this experiment support that there is a generalized plant gas exchange response to leaf-mass consumption injury.