Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2008
Publication Date: 12/1/2008
Citation: Hix, R., Kairo, M., Reitz, S.R. 2008. Does secondary plant metabolism provide a mechanism for plant defenses in the tropical soda apple Solanum viarum (Solanales: Solanaceae) against the beet armyworm Spodoptera exigua and southern armyworm S. eridania? Florida Entomologist. 91:566-569. Interpretive Summary: Insect feeding damage to plants can have consequences for both the plant and the insect itself, and other insects that may feed on the plant. While these phenomena have been studied in crop plants, little information exists for these interactions in weeds. Therefore scientists with Florida A&M University and USDA-ARS-CMAVE and affiliated with the Center for Biological Control determined how tropical soda apple responds to feeding by beet armyworm and southern armyworm caterpillars. Tropical soda apple is a key weed pest of pastures in the southern USA and related to tomato. The beet armyworm and southern armyworm are polyphagous pests that attack many crops. Feeding by both of these species appears to induce defensive chemical production in tropical soda apple. Significantly fewer armyworm caterpillars survived when allowed to feed on tropical soda apple plants that had been fed on by other caterpillars previously. This study is the first to document the effect of insect feeding on tropical soda apple and the results indicate that insect feeding will have implications for the ability of other pest and beneficial insects (including biocontrol agents of tropical soda apple) to feed and survive on tropical soda apple.
Technical Abstract: Survival assays were conducted with beet armyworm Spodoptera exigua and southern armyworm S. eridania with tropical soda apple Solanum viarum a relative of tomato. In addition, polyphenol oxidase (PPO) enzyme assays were conducted to determine if secondary plant defense compounds are being produced by tropical soda apple in response to herbivory. Both Spodoptera exigua and S. eridania appear to induce secondary plant defenses in tropical soda apple. Significantly more S. exigua and S. eridania neonate larvae survived to 2nd instar on non-induced plants and artificial diet when compared with plants with induced defenses. Tropical soda apple plants fed on by S. exigua and S. eridania had significantly increased PPO activity.