Location: Chemistry Research2011 Annual Report
1a. Objectives (from AD-416)
1. Determination of phsiological and biochemical mechanisms, elicitors, and regulators involved in the interactions of plants with insects and their natural enemies. 1a. Isolation and identification of elicitors or biotic agents of induced plant volatile emission and other inducible plant defenses. 1b. Elucidation of the signalling interactions that mediate insect and insect elicitor induced plant defenses and volatile emission. 2. Identification and evaluation of chemicals that regulate or influence behaviors, including foraging, mating and oviposition, of important pest insects. 2a. Isolate and identify plant volatiles and insect produced pheromones that in combination attract male and female pepper and cranberry weevils. 2b. identification of oviposition deterring pheromone from pepper weevil. 2c. Interaction between Insect and Host Volatiles on Reproductive Development of Anastrepha spp. (Dipera:Tephrididae). 2d. Identification of oviposition deterring pheromones for Tephritid Fruit Flies. 2e. Influence of Fruit Volatiles on attraction of Small Hive Beetle.
1b. Approach (from AD-416)
Identify and evaluate chemicals that regulate or influence behaviors, including foraging, mating and oviposition, of important pest insects. Determine the physiological and biochemical mechanisms, elicitors, and regulators involved in the interactions of plants with insects, insect natural enemies and other organisms. This research will utilize numerous interactive bioassays with insects, plants, purified biochemicals and other organisms. Isolation and identification of new bioactive chemicals that mediate insect behaviors and plant-insect interactions will be achieved using a combination of approaches including preparative GC, HPLC, preparative flash chromatography, GC/MS, FT-IR, NMR, micro-degradation and synthesis where applicable. Major target insects for this research will include pest Lepidoptera, Coleoptera and Diptera that attack fruit and vegetables and coleopteran pests of Honey Bees. Other target insects may be selected as needed during progression of the project.
3. Progress Report
Studies were conducted to measure maize defense responses to European corn borer tunneling in stems and the effect of these phytochemical changes on larval growth. Results showed that, despite increases in numerous phytohormone signals and subsequent defense-related metabolites, European corn borer growth on tissues previously challenged for 24 hours was not significantly inhibited. This work represents a starting point in the mechanistic understanding of how European corn borers overcome inducible plant defenses in maize. Studies were initiated to identify all of the additive and interactive components of the cranberry weevil pheromone blend to enable development of an improved monitoring trap. Similar studies to elucidate pepper weevil attraction demonstrated that virgin females and males preferred volatiles of plants fed on by males, which contained a combination of male aggregation pheromone and plant volatiles. The interactive role of role of herbivore-induced volatiles and male aggregation pheromone is currently being evaluated. A series of harmless mineral and organic deterrents were compared to commercial pesticides in both the laboratory and field plots to assess their effectiveness in reducing pepper weevil feeding and oviposition. In multiple field trials under heavy pepper weevil infestation, the mineral and organic deterrents resulted in marketable yields and performed equally to the standard pesticide treatments. Studies were conducted to identify natural products that regulate oviposition deterrence and attraction for pepper weevils. Solvent extractions were performed on large scale collections of female oviposition plugs to find behavioral modifying chemicals. Normal-phase chromatography was used to isolate both attractive and deterrent fractions which were then analyzed by gas chromatographic-mass spectrometric (GC-MS). Collection of volatiles emitted directly from oviposition plugs were also assayed for biological activity. One volatile chemical from plugs elicited attraction and searching behavior by female weevils. These studies provide critical information useful in the development of semiochemical mediated control programs for pepper weevils based ‘push-pull’ strategies.
1. Novel defenses in corn protect against insects and pathogens. The European corn borer and stalk rotting pathogens result in over one billion U.S. dollars in economic loss each year yet plant resistance mechanisms against these threats remain poorly understood. To better understand corn stalk defenses, metabolic profiling was utilized to search for elevated metabolite levels following insect and pathogen attack. Using this approach, ARS researchers at Gainesville, Florida identified a series of six related and highly inducible acidic diterpenoids, termed kauralexins, that exhibit significant antifungal and insect antifeedant activity. Importantly the gene An2, encoding an ent-copalyl diphosphate synthase, was strongly implicated in the regulating the biosynthesis of these defenses and is a target for manipulation. The discovery of these chemical defenses and associated metabolic pathways opens the door to targeted selective breeding and ultimately manipulation of these processes to improve crop plant resistance in the field.
Cha, D.A., Linn Jr., C.E., Teal, P.E., Zhang, A., Roelofs, W.L., Loeb, G.M. 2011. Eavesdropping on plant volatiles by a specialist moth: significance of ratio and concentration. PLoS One. 6(2):1-8.