2013 Annual Report
1a.Objectives (from AD-416):
To sequence the transcriptome of the polyphagous shot hole borer (Euwallacea sp.) in order to improve our understanding of the biology and physiology of this important invasive insect pest and identify candidate genes potentially involved in insecticide resistance.
1b.Approach (from AD-416):
The polyphagous shot hole borer (Euwallacea species) is a recently discovered ambrosia beetle that is causing Fusarium dieback on avocado and other host plants in and near Los Angeles and Orange Counties. The disease is caused by a new Fusarium species that is a fungal symbiont of the polyphagous shot hole borer. Females bore galleries into the host tissue and vector the new Fusarium species, which subsequently impairs the vascular system of the tree and leads to dieback. Known hosts include box elder (Acer negundo), castor bean (Ricinus communis), avocado (Persea americana), English oak (Quercus robur), California coast live oak (Quercus agrifolia), big leaf maple (Acer macrophyhllum), silk tree (Albizia julibrissin), liquidambar (Liquidambar styraciflua), coral tree (Erythrina coralladendron), titoki tree (Alectryon excelsus), California sycamore (Platanus racemose), and blue palo verde (Cercidium floridum). The borer and associated fungus have been found on avocado trees at commercial groves, arboretums, and residences in Los Angeles and Orange Counties. Chemical control has not been effective at preventing attacks by the polyphagous shot hole borer.
The polyphagous shot hole borer is morphologically similar to the tea shot hole borer, Euwallacea fornicates, but genetic analyses have characterized large differences in DNA sequences between the two organisms. No information on the functional genomics of the polyphagous shot hole borer is currently available, which hinders our understanding of the insect’s biology, potential resistance to insecticides, and ability to adapt with environmental stress conditions. The development of second-generation sequencing such as 454 pyrosequencing and Illumina/Solexa provides an opportunity to study the functional genomics of non-model organisms for which little molecular knowledge exists, such as the polyphagous shot hole borer. These pyrosequencing techniques have been used to unravel transcriptomic information for insects such as the pine shoot beetle, Tomicus yunnanensis, emerald ash borer, Agrilus planipennis, the tobacco hornworm, Manduca sexta, the soybean aphid, Aphis glycine, and the poplar leaf beetle, Chrysomela tremulae. Results obtained from these studies will establish a basis for future functional genomic studies, improve our understanding of the biology and physiology of this important invasive insect pest, and identify candidate genes potentially involved in insecticide resistance.
Since male polyphagous shot hole borers are flightless and uncommon, RNA will be extracted from intact adult females. A cDNA library will then be constructed for subsequent Illumina sequencing. A bioinformatics analysis will then be conducted using the Illumina data processing pipeline or an equivalent approach, along with database searches for known gene sequence functions.
The polyphagous shot hole borer (PSHB) (Euwallacea species) is an exotic ambrosia beetle that is attacking avocado and other trees in and around Los Angeles and Orange Counties. In order to sequence the transcriptome of the PSHB, ARS made arrangements with the collaborator to obtain freshly preserved specimens. Adult female PSHB were collected in November 2012 in Pasadena, California from the bark of highly infested box elder trees, Acer negundo, and then shipped in an appropriate buffer to Wooster, Ohio. A second collaborator then isolated RNA from the specimens, which was sent to the Purdue Genomics Core Facility (West Lafayette, IN) for constructing cDNA libraries and subsequent deep sequencing using next generation sequencing technology. The sequencing efforts resulted in a total of 148,399 high quality sequences for the PSHB, which represents the first database created for this insect pest. Current efforts are focused on annotating and assigning function to these sequences. Genes of interest potentially involved in important biological processes, such as insecticide detoxification, are currently being identified within this huge database. Such information will provide key insight into the adaptability of this insect at the molecular level.
This research relates to the following objectives of the parent project: (1) to reduce, through knowledge generated by research, crop losses and damage caused by insect pests of ornamental nursery crops, turf, and other horticultural crops; (2) to develop alternative management strategies for pest control that will reduce dependence upon traditional uses of insecticides, and lessen impact on groundwater.