1a. Objectives (from AD-416):
The goal of this project is to develop innovative and sustainable technologies to manage insect pests and their natural enemies to reduce damage to trees, shrubs, and flowering perennial plants in managed and unmanaged urban landscapes. Lepidopteran and coleopteran pests are the principal defoliators in urban landscapes and nearby forests, and constitute 60% of recorded invasive insect species in North America. The research focuses on five of the most destructive lepidopteran and coleopteran pests in urban landscapes: gypsy moth, winter moth, and dogwood borer; and emerald ash borer and Asiatic garden beetle; however, research results are expected to be broadly applicable to other urban landscape insect pests. The research is organized around three objectives: (1) identify and synthesize plant-derived semiochemicals and insect pheromones attractive to pests, and design insect monitoring and management strategies employing them; (2) develop microbial and arthropod natural enemies as biocontrol agents of native and exotic pests of landscape plants; and (3) identify at the molecular level genes and gene pathways critical for success of landscape pests; employ molecular technologies to determine the role of host pathways targeted by entomopathogens; and target these pathways with natural or molecular biopesticides to kill pests.
1b. Approach (from AD-416):
This highly interdisciplinary project combines concepts and methodologies from analytical and synthetic organic chemistry, insect chemical behavior, insect pest-pathogen genomics, and microbial and insect ecology to develop strategies to combat urban landscape pests. Plant-derived semiochemicals and insect pheromones will be identified, and novel chemical and biological syntheses will be devised to enable their use for monitoring pest populations, disrupting pest reproduction, and luring pests into traps to be exposed to pathogenic microorganisms. Ecological attributes of pathogens underlying virulence, specificity, and accessibility to hosts will be determined. Transcriptome analysis of gypsy moth larvae challenged with various classes of pathogens will expose insect molecular vulnerabilities exploited by virulent pathogens. Naturally occurring pathogens best able to exploit these vulnerabilities will be applied directly to the environment, or placed in traps with species-specific semiochemicals to lure pests into contact with the pathogens to initiate epizootics. Experimental native and exotic assemblages of woody and herbaceous urban landscape plants will be characterized according to the natural enemy resources that they provide, and tested for their ability to support natural enemies and thereby to promote effective biocontrol of urban landscape pests.
3. Progress Report:
Objective 1: Identify and synthesize plant-derived chemicals and insect pheromones attractive to pests; design pest monitoring and management strategies employing them. Two approaches to producing 7-epi-sesquithujene (7ES), a long-distance attractant for the emerald ash borer (EAB). The Asian invasive EAB threatens all native ash species. First, we made insect virus vectors that carry the TPS4 gene, which directs synthesis of 7ES, but they did not produce TPS4 in insect cells. Though we successfully introduced alternative non-viral vectors into insect cells, the cells became contaminated with fungus, indicating a need for new methods. We then developed a synthesis for 7ES using commercially available chemicals. 7ES was not an effective EAB lure in field traps, either alone or in combination with (3Z)-hexenol, a generalized insect attractant. We plan further field tests of 7ES as an EAB attractant. Objective 2: Develop microbial and arthropod natural enemies as biocontrol agents of landscape plant pests Virulent new gypsy moth (GM) nucleopolyhedrovirus (NPV) isolates. GM is the most serious landscape pest in the US, and new biocontrol agents are needed. NPVs from Asia and Massachusetts (MA) were tested for toxicity against GM caterpillars along with Gypchek, the NPV product used by the Forest Service. MA and Russian isolates were about twice as toxic as Gypchek. Genetic analysis of these and several other isolates found that the Asian isolates are separate and distinct from North American and European isolates. Asian isolates appear to be more toxic against Asian GM than Gypchek. Native parasitoids are more diverse in native than exotic urban landscapes. Native natural enemies are expected to be more effective biocontrol agents on native than on exotic plants. In a residential-scale experiment, we found that parasitic wasps are more abundant, and comprise more species, in habitats dominated by native than by exotic plants. Objective 3: Identify gene pathways critical for success of landscape pests; use molecular methods to identify host pathways targeted by insect pathogens; target them with natural or molecular bio-insecticides. RNA interference (RNAi) for brown marmorated stink bug (BMSB) and gypsy moth (GM) control. RNAi deactivates specific genes to disable a target organism. To identify molecular targets for an RNAi strategy against BMSB, a devastating exotic and invasive landscape pest, we determined the total complement of active genes - the transcriptome - in different BMSB stages and both sexes. In the process we recovered the complete gene sequence of a novel virus that may be useful as a BMSB biocontrol agent. For GM, we analyzed transcriptomes to compare active genes in tissues of healthy GM caterpillars, versus those infected with the bacterium Bacillus thuringiensis, the fungus Varimorpha dispar, or a second bacterium. Differences in levels of gene transcription (copying from DNA to RNA) in healthy and infected tissues revealed ten candidate GM-specific RNAi targets. These are being tested for efficacy in live caterpillars.
1. Comparison of healthy versus Bacillus thuringiensis (Bt)- infected gypsy moth genetic components revealed important genes that could be involved in resistance development or biological control. Gypsy moth (GM) is the most serious woody landscape pest in the U.S. Nevertheless, almost no genetic information existed for GM, even though this information could help scientists devise new biological control strategies and understand development of resistance to biocontrol and other management strategies. We determined the total genetic components, called the “transcriptome”, produced in midgut tissue in healthy and in Bacillus thuringiensis (Bt)-infected GM caterpillars. High-throughput approaches were used to assemble and analyze gene expression (activity) profiles. The genes exhibiting increased or reduced activity in response to Bt infection were primarily associated with functions of digestion; immune response; development; or binding (acid-, lipid-, protein-, or nucleic acid-binding). This is the first study using large-scale sequencing technologies to specifically investigate how GM responds to a bacterial infection challenge. The results highlight important genes that could be involved in biopesticide resistance development, or could serve as targets for new biopesticides in biologically-based control strategies of this devastating pest.
Blackburn, M.B., Martin, P.A., Kuhar, D.J., Farrar, R.R., Gundersen, D.E. 2013. Phylogenetic distribution of phenotypic traits in bacillus thuringiensis analyzed by multilocus sequence typing . PLoS One. 8(6):e66061.