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Entomopathogenic nematodes and parasitoid wasps are used as biological control agents for management of insect pests such as the Indian meal moth, Plodia interpunctella. The parasitoid wasp Habrobracon hebetor injects a paralytic venom into P. interpunctella larvae before laying eggs. A previous study reported that the entomopathogenic nematode Heterorhabditis indica preferentially infects P. interpunctella that have been envenomed by H. hebetor while results in this study showed a similar preference by the entomopathogenic nematode, Steinernema glaseri. We therefore tested four hypotheses for why nematode infection rates are higher in envenomed hosts: (1) elevated CO2 emission from envenomed hosts attracts nematodes, (2) paralysis prevents hosts from escaping nematodes, (3) volatile chemicals emitted from envenomed hosts attract nematodes and increase infection, and (4) reduced immune defenses in envenomed hosts increase nematode survival. Results showed that envenomed P. interpunctella larvae emitted lower amounts of CO2 than non-envenomed larvae. Physical immobilization of P. interpunctella larvae did not increase infection rates by S. glaseri but did increase infection rates by H. indica. Emissions from envenomed hosts were collected and analyzed by thermal desorption gas chromatography/mass spectrometry. The most abundant compound, 3-methyl-3-buten-1-ol, was found to be an effective cue for S. glaseri attraction and infection but was not an effective stimulus for H. indica. Envenomed P. interpunctella exhibited a stronger immune response toward nematodes than non-envenomed hosts. Altogether, we conclude that different mechanisms underlie preferential infection in the two nematode species: host immobilization for H. indica and chemical cues for S. glaseri.

Inconsistency in entomopathogenic nematode (EPN) efficacy is still one of the biggest challenges for the wider adoption of EPNs as biocontrol agents. Previous studies demonstrated that extracts from EPN-infected hosts enhance dispersal and efficacy, two key factors in success of EPNs. Some active components in the insect host cadavers responsible for dispersal, ascarosides, have been identified as nematode pheromones. We hypothesized that pheromone extracts increase dispersal of EPN infective juveniles (IJs) leading to increased efficacy. First, we determined whether pheromone extracts improved IJ movement/dispersal in soil columns baited with Tenebrio molitor larvae. We found that pheromone extracts induced higher numbers of Steinernema carpocapsae and Steinernema feltiae IJs to move towards T. molitor larvae in the bottom of the column compared to IJs treated with infected cadaver macerate and water, positive and negative controls, respectively. Furthermore, the number of S. carpocapsae IJs that invaded T. molitor larvae was higher for the pheromone extract treatment than the controls. S. feltiae IJs that were pretreated with pheromone extracts and macerate (positive control) infected T. molitor at the same rate but invasion was superior to IJs that were treated with water. Consistent with the soil column tests, both S. carpocapsae and S. feltiae IJs treated with pheromone extracts performed better in killing larvae of two economically important insect larvae, pecan weevil, Curculio caryae, and black soldier fly, Hermetia illucens, in greenhouse tests compared to IJs treated with water. We demonstrated pheromone-mediated behavioral manipulation of a biological control agent to enhance pest control potential. Conceivably, nematodes can be exposed to efficacy-enhancing pheromones prior to field application.

Above ground herbivory can induce release of plant volatiles that attract natural enemies of the herbivores. Similarly, roots can release herbivore induced volatiles that attract beneficial organisms such as entomopathogenic nematodes belowground. Unlike their aboveground counterparts, belowground volatile signals interact with solids, liquids, and gases as they move through soil pore spaces. These interactions influence belowground signaling, can create non-linear diffusion profiles, and result in surface adsorbtion and degradation of volatiles in space and time. By examining diffusion and degradation in sand-filled microcosms, we found that the diffusion profiles of E-β-caryophyllene, d-limonene, pregeijerene, α-pinene, germacrene-d, and linalool were affected by moisture and pH. Furthermore, the common plant volatile linalool was non-diffusive below ground. In addition, we discovered a novel pathway for the degradation of linalool into rapidly diffusing belowground signals. These findings suggest areas for future exploration and highlight the importance of abiotic factors when studying belowground semiochemically-based interactions such as attraction of beneficial entomopathogenic nematodes to plant roots infested by host insects.

Little is known regarding insect defense pathways in Setaria viridis (setaria), a model system for panicoid grasses, including Zea mays (maize). It is thus of interest to compare insect herbivory responses of setaria and maize. Here we use metabolic, phylogenetic, and gene expression analyses to measure a subset of jasmonic acid (JA)-related defense responses to leaf-chewing caterpillars. Phylogenetic comparisons of known defense-related maize genes were used to identify putative orthologs in setaria, and candidates were tested by quantitative PCR to determine transcriptional responses to insect challenge. Our findings show that while much of the core JA-related metabolic and genetic responses appear conserved between setaria and maize, production of downstream secondary metabolites such as benzoxazinoids and herbivore-induced plant volatiles are dissimilar. This diversity of chemical defenses and gene families involved in secondary metabolism among grasses presents new opportunities for cross species engineering. The high degree of genetic similarity and ease of orthologous gene identification between setaria and maize make setaria an excellent species for translational genetic studies, but the species specificity of downstream insect defense chemistry makes some pathways unamenable to cross-species comparisons.

Fused-silica columns of 0.22 mm I.D. packed with normal small-particle high-performance liquid chromatography packing material were studied. The shape of the column end allows direct connection to a combined electron impact—chemical ionization (EI—CI) ion source. To inject small volumes a syringe-loaded micro-sample injector is used with the time splitting technique. Mass spectra obtained from easily vaporized compounds are similar to, but display less thermal decomposition than, normal EI spectra. Mass spectra of underivatized native mono- and disaccharides give useful structural information. Results from the analysis of cardiac glucosides are also shown. The system provides high-efficiency chromatography with a universal detector, suitable for the analysis of non-volatile and labile compounds.

Fused-silica columns (I.D. 0.22 mm) packed with ordinary small particle liquid chromatographic material were used in direct connection to an electron impact ion source. The electrostatic field between the column end and an extraction—focusing plate, located close to the ion source inlet, was used for nebulization of the solvent. The ion source was modified to obtain higher efficiency and to reduce the thermal decomposition of labile compouds. A system for micro flow gradients (less than 2 μl/min) has been developed. The flow of a pumping medium (glycerol) is divided into two parallel streams and the flow distribution is controlled using the temperature depedence of the viscosity. The glycerol flow is changed by two “media converters” to the chromatographic solvents. Applications of micro liquid chromatography—mass spectrometry are shown for a plant allelochemical, dhurrin, obtained from Sorghum leaf extract. Mass spectra of glucose, neral, geranial, chlorsulphuron, myoinositol, 3,5,-dinitrobenzoic acid, amtriptyline, 10-hydroxyamitriptyline and omeprazole after liquid chromatography are shown.

Fused-silica columns (I.D. 0.22 mm), packed with ordinary small-particle HPLC packing material, were directly connected with an electron-impact ion source. A system for micro flow gradient (1–5 μl/min) has been developed. The electrostatic field between the column end and the ion source is the major factor for nebulization. The electrostatic effect was studied with regard to different column tip designs. Experiments with focusing of the solvent spray to increase the sensitivity are also presented. Applications to plant extracts, phenolic acids and other polar compounds are reported.