1a. Objectives (from AD-416):
1. Prevent invasions of chilli thrips and whiteflies by developing genetic tools to track/predict/monitor and ultimately aid in controlling movement from likely sources of infestation and suppress established populations with biologically-based and environmentally-sound techniques. 1a. Determine the global sources of invasive chilli thrips, Scirtothrips dorsalis and describe the global genetic diversity of this pest species so that effective international and national barriers can be erected to further introductions. 1b. Investigate biological control and ecological interactions of chilli thrips and whiteflies with their natural enemies in order to promote their environmentally sound control in vegetable and ornamental crops 2. Investigate structural, physiological, molecular and chemical aspects of the whitefly feeding process and identify inhibitor strategies/molecules that can be used in the development of novel interdiction strategies envisioned to work either through production of transgenic plants or application of chemical treatments that block feeding. 2a. Characterize the method of polymerization that occurs when whitefly saliva is secreted and solidifies during insect probing for the plant vascular tissue. 2b. Determine the structural composition of salivary sheaths and the source of the precursors. 2c. Identify small molecule inhibitors of the whitefly feeding process using the artificial diet system as a bioassay.
1b. Approach (from AD-416):
Research will focus on establishing a DNA barcoding reference data set for S. dorsalis that will allow construction of a robust global molecular phylogeny for this species using both mitochondrial cytochrome oxidase I (mtCOI) and nuclear genes to be identified. A commercially available predatory mite (Amblyseius swirskii) will be evaluated for sustainable control of chilli thrips, whiteflies and other key pests in ornamental and vegetable crops using banker plants and ‘predator-in-first’ tactics. Molecular and biochemical methods will be used to develop a model describing whitefly salivary sheath formation and to identify inhibitors of this process that can be evaluated for use in control strategies.
3. Progress Report:
India is thought to be the likely geographical origin of chilli thrips, Scirtothrips dorsalis. To help determine the phylogenetic placement of this species within the genus thirty variants of a mitochondrial gene from chilli thrips collected in India were sequenced. Primers were then developed that improved the success rate for amplifying and sequencing this gene from a greater diversity of chilli thrips samples globally. Chilli thrips mitochondrial haplotypes from Japan are more than 14% divergent from other chilli thrips samples and are consistent with findings from morphometric analysis of five geographically distinct populations. Eleven varieties of hot pepper and 17 varieties of sweet pepper were screened for their ability to sustain the predatory mite, Amblyseius swirskii, with/without pollen. Five hot peppers sustained an average of 8-12.7 mites per seedling for 70 d post release. Among 17 selected sweet pepper varieties, 8 maintained the most mites and 9 varieties effectively sustained mites when supplemented with pollen. Overall, four varieties maintained the higheset predatory mite populations for at least 45 d averaging 5.5 mites per plant. Functional response studies showed that the predatory mite, Amblyseius swirskii, reared on different diets (peach, cattail, ornamental pepper pollen, and other prey) was equally effective against chilli thrips nymphs. Among these diets, the maximum daily predation was 35-43 nymphs of chilli thrips/day by an A. swirskii female. The findings improve the ability to rear predatory mites for biological control against multiple pests in vegetable and ornamental production. Tomato yellow leaf curl virus and its vector, the sweetpotato whitefly, threaten the economic value of greenhouse tomato production. We demonstrated the use of Papaya plants could be used as a banker plant to conserve wasps that, in turn control this whitefly. Our lab also showed that ‘Maradol’ papaya is not a host for tomato yellow leaf-curl virus strengthening the case for growers to use the papaya banker plant system for whitefly control. We have successfully developed an optimized strategy to use Flinders Technology Associates DNA storage card technology to archive DNA from arthropod samples using a new quick-boil method that recovers DNA from the card in five minutes for less than $0.01 per reaction. Research on B. tabaci saliary sheaths was problematic due to inability to obtain pure sheaths. Complications in the isolation procedure led to extended research on new method of purification. A novel method for B. tabaci salivary sheath isolation was developed using soluble membranes through which whitefly pierces and produces a salivary sheath that remained attached to the membranes. Large quantities of pure salivary sheaths were obtained using this method in combination with a filtration strategy. This method worked for numerous plant feeding hemipteran insects and allows isolation of large quanties of salavary sheaths per compositional structural and biosynthetic analysis. Initial salivary sheath composition analysis revealed a structure primarily composed of a specific carbohydrate polymer with protein crosslinks.
Dickey, A.. Osborne, L.S., McKenzie, C. 2012. Papaya is not a host for tomato yellow leaf-curl virus. Florida Entomologist. 95:211-213. Available: http://dx.doi.org/10.1653/024.095.0136