Application of Two-spotted Spider Mite Tetranychus urticae for Plant-pest Interaction Studies

Summary

Protocols for efficient preparation of homogenous samples of spider mites, infestation of experimental plants, and assessment of plant damage, as required for studies of plant-pest interaction were developed.

Abstract

The two-spotted spider mite, Tetranychus urticae, is a ubiquitous polyphagous arthropod herbivore that feeds on a remarkably broad array of species, with more than 150 of economic value. It is a major pest of greenhouse crops, especially in Solanaceae and Cucurbitaceae (e.g., tomatoes, eggplants, peppers, cucumbers, zucchini) and greenhouse ornamentals (e.g., roses, chrysanthemum, carnations), annual field crops (such as maize, cotton, soybean, and sugar beet), and in perennial cultures (alfalfa, strawberries, grapes, citruses, and plums)^1,2. In addition to the extreme polyphagy that makes it an important agricultural pest, T. urticae has a tendency to develop resistance to a wide array of insecticides and acaricides that are used for its control^3-7.

T. urticae is an excellent experimental organism, as it has a rapid life cycle (7 days at 27 °C) and can be easily maintained at high density in the laboratory. Methods to assay gene expression (including in situ hybridization and antibody staining) and to inactivate expression of spider mite endogenous genes using RNA interference have been developed^8-10. Recently, the whole genome sequence of T. urticae has been reported, creating an opportunity to develop this pest herbivore as a model organism with equivalent genomic resources that already exist in some of its host plants (Arabidopsis thaliana and the tomato Solanum lycopersicum)¹¹. Together, these model organisms could provide insights into molecular bases of plant-pest interactions.

Here, an efficient method for quick and easy collection of a large number of adult female mites, their application on an experimental plant host, and the assessment of the plant damage due to spider mite feeding are described. The presented protocol enables fast and efficient collection of hundreds of individuals at any developmental stage (eggs, larvae, nymphs, adult males, and females) that can be used for subsequent experimental application.

Introduction

Plant-pest interaction is a topic of great scientific and economic importance. It was historically studied using both crop plants (such as tomato) and the model plant, A. thaliana. In both cases, susceptibility of plant to herbivore could be measured either directly through assessment of plant phenotype after herbivore attack or indirectly through the assessment of pest performance.

Direct measurements of plant susceptibility were utilized previously for a number of insect pest species using a range of methods. For example, herbivory of lepidopteran larvae is measured as an estimation of the portion of plant tissue consumed by eith....

Protocol

1. Maintenance of the Spider Mite Population

NOTE: Spider mites are reared on California red kidney beans (Phaseolus vulgaris).

1. Grow bean plants from seeds for 2-3 weeks prior to infestation.
2. Intermix these plants with infested plants; adult mites will rapidly colonize fresh plant material.
3. Remove old infested bean plants every 7-10 days, replacing them with fresh plants.

2. Collecting Adult Female Mites

1. Mite Collection using the Washing Method
   1. To collect mites, place a fresh bean plant in contact with infested plants 1 to 2 days prior t....

Results

Using 20 to 30 infested bean plants, one can collect around 2,000 adult female mites using sieves. The time required to infest 10 plants with 20 mites per plant is approximately 15 min if using a brush to transfer mites. Combinations of collection and application methods are shown in Figure 2.

This protocol generates reproducible results of plant damage, demonstrating that collected mites are of similar physiological state and suitable for plant-spider mite interaction studies.......

Discussion

This video demonstrates protocols used to isolate and to infest plants with large numbers of adult female mites. Although we presented this protocol using A. thaliana, it can be used for any plant-spider mite interaction system and is currently being successfully applied also on tomato and grapevine (Vitis vinifera) plants. The protocol yields reproducible results, indicating that collected mites are of comparable physiological state (Figure 3).

While th.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Plant material:
California red kidney bean	Stokes, Thorold, ON, Canada		2 week old, well infested with spider mites 2 or 3 days before use. Other cultivars of Phaseolus vulgaris can be used.
Chemicals:
Tween 20	Sigma-Aldrich	P9416	1% stock solution is prepared to simplify aliquoting
Tap water			At room temperature, heat- and cold-shock affect mite survival rate and performance
Other materials and equipment:
Plastic tray
Set of scissors
2 L beakers
Paper towels
Sets of sieves	Manufactured in house		Detailed instructions are available
Thin brush
Pipettes
Pipette tips			0.2 and 1 ml
1.5 ml centrifuge tubes
Air pump			Aquarium type pump with inverted air flow. Vacuum line can be used. Required pressure drop is approx. 2-4 psi
Stereoscope
Scanner	Epson	V30	Any flatbed scanner allowing necessary degree of control over scan quality. We use Epson V30 for our experiments.
Computer			Windows or OS X PC which is compatible with scanner hardware and Adobe Photoshop software.
Adobe Photoshop software	Adobe Systems Inc., San Jose, CA, USA	various	Any version with Histogram tool included.