1a. Objectives (from AD-416):
This project has the long-term objective to develop and improve diverse biologically based controls for insects in vegetable crops for urban small farms and gardens, considering both organic and non-organic production. Research will target insect pests that cause major damage to several of the most common crops in small vegetable farms and gardens in urban settings, and for which there is potential to shift from synthetic chemical control strategies to bio-based strategies. The main focus will be pests of cole crops, cucurbits, and vegetable seeds and seedlings, although other important crops may receive attention for specific problems. The specific objectives are to: (1) Identify, synthesize (including in vitro biosynthesis) and evaluate semiochemicals to manage significant insect pests of small farms and gardens; (2) Discover and develop systems to conserve and augment key natural enemies of small farms and gardens, using pheromones and other attractants, specially-adapted crop cultivars, and food provisioning through plant and supplemental sources; (3) Identify effective microbial controls for key pests of small farms and gardens, including discovery of molecular and ecological mechanisms for sustained field reproduction and persistence, using Bt, baculoviruses, and other entomopathogens; (4) Determine genetic basis of plant defense mechanisms of high-value crops of small farms or gardens (such as cole crops) against destructive insects, including pest aversion and resistance; and (5) Develop predictive tools for measurement of pest suppression and damage for evaluation of farm and garden habitats.
1b. Approach (from AD-416):
The project brings together a research team with diverse expertise for multiple approaches to insect management. Those approaches will include discovery, commercially-viable synthesis, and deployment of natural insect attractants for harlequin bug, brown marmorated stink bug, other pestiferous true bugs, and striped cucumber beetle, using electrophysiology and diverse cutting-edge chemical diagnostic methods, multipronged methods of chemical and in vitro sythesis, formulation development, and investigation of insect behavioral response in the field. Conservation and augmentation of generalist predators (including predatory stink bugs and lacewings) will use existing and discovered male-produced aggregation pheromones, coupled with new approaches to assessing biological control impact on important vegetable pests. Pest-specific microbial controls will be targeted to identify and evaluate bacterial strains (particularly Bt) which can survive and colonize crops under field conditions, and baculoviruses which are efficacious against key vegetable pests. Plant resistance investigations for cole crops will take an innovative approach using molecular-based gene discovery. The combination of semiochemical and biological controls, including microbial controls, and crop resistance, will offer a range of non-chemical tactics useful to a bio-based integrated pest management strategy for major vegetable pests in urban small farms and gardens.
3. Progress Report:
Objective 1: Identify, synthesize, and evaluate semiochemicals. Harlequin bug aggregation pheromone is being deployed, both in experimental field bioassays in Maryland, and on small farms and gardens with susceptible crops, using potted host plants to develop effective management strategies including pheromone-augmented “super trap plants.” We have tested natural products that deter feeding in brown marmorated stink bug laboratory bioassays, and under field conditions. Results suggest that formulation and dispenser are critical to provide field crop protection. Research is underway on host and pheromone volatiles that attract adult squash bugs. We are examining ovipositional preferences of squash bug for different cultivars of Cucurbita pepo. We attempted to identify and clone a candidate polyketide synthase gene from striped cucumber beetle to biosynthesize its aggregation pheromone, vittatalactone, using several approaches, but were unable to identify candidate genes. This suggests that vittatalactone synthesis is very different from known polyketide synthesis in other organisms, or that vittatalactone has a plant polyketide precursor. We are also undertaking challenging chemical syntheses for vittatalactone in gram quantities. Efforts to make racemic vittatalactone are approaching conclusion after several exploratory synthetic routes. Objective 2. Discover and develop systems to conserve and augment key natural enemies. We are working with a commercial partner for a product based on iridodial attraction of wild lacewings, with plant volatiles and semiochemicals to attract a spectrum of beneficial insects. Methods for enhancing squash bug egg parasitism and predation are under study; 2012 studies indicated high rates of egg parasitism and parasitoid emergence. Objective 3. Identify effective microbial controls for key pests of small farms and gardens. We produced and tested a wheat bran bait formulation of black cutworm baculovirus isolates for field use; larvae fed on the bait and succumbed to baculovirus infection. To improve field persistence of Bt, we seek strains with ability to translocate through plants and/or to grow on leaf surfaces. We have identified a caterpillar-toxic strain which grows on cabbage extract, an indicator of ability to grow within or on the plant. Recent publications indicate a genetically similar strain can be taken up from soil and translocated in cabbage. Novel bacteria belonging to the order Neisseriales, isolated from a sphagnum bog, were found to be toxic to larvae of diamondback moth, a key cole crop pest. In addition, nine highly related spore-forming bacteria were identified with control potential on rangeland pest insects. Objective 4. Determine genetic basis of plant defense mechanisms of cole crops. Over-expression of a transcription factor controlling gene expression in the model plant Arabidopsis leads to greater resistance to cabbage looper, a key pest of cole crops. Plants with this factor had less leaf damage and insects gained less weight. This type of plant resistance should be more resilient, since it involves expression of numerous genes -- which are now being examined in depth.
Breitenbach, J.E., El-Sheikh, E.A., Harrison, R.L., Rowley, D.L., Sparks, M., Gundersen, D.E., Popham, H.J. 2013. Determination and analysis of the genome sequence of Spodoptera littoralis multiple nucleopolyhedrovirus. Virus Research. 171(1):194-208.