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
Morphometric traits used for taxonomy of chilli thrips from five different geographical regions including Florida were compared. No differences were found for 14 morphological characters between Israel, India, St. Vincent, and Florida; however, these populations were different from Japan which agrees with our deoxyribonucleic acid (DNA) barcoding results suggesting that chilli thrips has distinct types and research is required to understand the biological significance of this variation. Further DNA barcoding research showed that typical sequences used for species verification of many eukaryotes will not work for chilli thrips. Intragenomic variation (variation within the genomes of different cells from the same individual) exists with the commonly used intragenic ribonucleic acid (RNA) gene sequence that is greater than what could be observed between different species. Traditional taxonomy using scanning electron microscopy was coupled with molecular techniques for deoxyribonucleic acid (DNA) barcoding to develop a novel diagnostic method for chilli thrips identification where a single specimen could be first used for identification and then analyzed molecularly. In the past, thrips had to be slide mounted for morphological identification and were destroyed or rendered unusable for molecular analysis. Predatory mite reproduction, development, adult longevity and survival (egg to adult) on leaf discs of ornamental pepper varieties were compared to two vegetables (tomato, green bean). The mite had similar reproduction, immature development time, adult longevity and survival rate on the ornamental peppers but laid few eggs and did not survive on either vegetable host with adult longevity similar to the filter paper control. Population dynamics of the predatory mite on ornamental peppers and two vegetables was evaluated in the greenhouse over time. Mites thrived on three varieties of ornamental pepper plants for long periods (60 days or more) without prey while mites died on both vegetables after 10 days. Population peaks coincided with blooming periods and mites preferred the top canopy of the plant possibly due to more leaf domatia and flowering activity. Predation studies using ornamental pepper as banker plants for dispersal of the predatory mite against whiteflies and thrips infested green bean demonstrated the mite’s ability to survive, reproduce, and provide excellent control on prey infested green bean. Predatory mites provided 94 and 99% control of thrips and whitefly, respectively. This banker plant system has the potential to control multiple pest species in commercial vegetable greenhouses. The feeding process of the whitefly requires the synthesis of a tube through which the piercing mouthparts probe into the host plant tissue while the insect searches for phloem cells on which to feed. This tube is called a salivary sheath and we show that it can be produced solely from secretions from the stylets of the insect and does not require plant components. We have also developed an artificial chamber in which these sheaths can be harvested and used these chambers to identify two inhibitors of salivary sheath formation.